Electric-Drive Propulsion for U.S. Navy Ships: Background and Issues for Congress

Order Code RL30622

CRS Report for Congress

Received through the CRS Web

Electric-Drive Propulsion for U.S. Navy Ships:

Background and Issues for Congress

July 31, 2000

(name redacted)

Specialist in National Defense

Foreign Affairs, Defense, and Trade Division

Congressional Research Service ˜ The Library of Congress

Electric-Drive Propulsion for U.S. Navy Ships:

Background and Issues for Congress

Summary

The Navy in January 2000 selected electric-drive propulsion technology for use

on its planned next-generation DD-21 land-attack destroyer and is considering it for

use on other kinds of Navy ships as well. Electric drive poses issues for Congress

concerning its costs, benefits and risks, and how the technology should be integrated

into the DD-21 program or other ship-acquisition programs.

Several foreign countries are developing or using electric drive in commercial or

naval ships. The U.S. Navy’s electric-drive development effort centers on the

Integrated Power System (IPS) program. Several private-sector firms in the United

States are now pursuing electric drive for the U.S. Navy market.

Electric drive offers significant anticipated benefits for U.S. Navy ships in terms

of reducing ship life-cycle cost, increasing ship stealthiness, payload, survivability, and

power available for non-propulsion uses, and taking advantage of a strong electricalpower technological and industrial base. Potential disadvantages include higher nearterm costs, increased technical risk, increased system complexity, and less efficiency

in full-power operations. The current scarcity of precise and systematic estimates of

the costs and benefits of electric drive makes it difficult for policymakers to assess the

relative cost-effectiveness of differing technical approaches to achieving electric drive.

Some of the risks involved in developing electric-drive technology have been

mitigated by the successful development of electric-drive technology for commercial

ships; estimates of the amount of remaining risk vary.

The Navy has stated that developing common electric-drive components is

feasible for several kinds of Navy ships and that pursuing electric drive technology in

the form of a common family of components could have advantages for the Navy.

The potential savings associated with a common system are difficult to estimate, but

could be substantial. The concept of developing a common system or family of

components poses issues for policymakers concerning the extent of commonality

across electric-drive-equipped Navy ships and the use of competition in the

development and procurement of electric-drive technology.

Much of the debate over electric drive concerns electric motors. The five basic

types in question – synchronous motors, induction motors, permanent magnet motors,

superconducting synchronous motors, and superconducting homopolar motors –

differ in terms of their technological maturity, power-density, and potential

applicability to different Navy ship types.

The Navy’s decision to use electric drive on the DD-21 raises several potential

issues concerning the acquisition strategy for the ship. Electric drive could be

installed on Virginia (SSN-774) class submarines procured in FY2010, according to

the Navy. Other candidates for electric drive include the Navy’s planned TADC(X)

auxiliary dry cargo ships, the Navy’s planned joint command and control (JCC[X])

ships, the second through fifth LHA replacement ships, future aircraft carriers, and

possibly the new cutters to be procured under the Coast Guard Deepwater project.

Contents

Introduction and Key Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Congressional Request . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Sources of Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Key Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Electric Drive in General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Application of Electric Drive to Specific Ship-Acquisition Programs . 9

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Basic Description of Electric Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Electric vs. Mechanical Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Integrated Electric Drive (Integrated Power System) . . . . . . . . . . . . 12

Key Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Common Electric Drive System . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

All-Electric Ship . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Motor Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Anticipated Benefits and Potential Disadvantages . . . . . . . . . . . . . . . . . . . 16

Anticipated Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Potential Disadvantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Brief History of Electric Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Current Status of Electric Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Outside the United States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

In the United States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Associated U.S. Navy Ship Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Navy Report to Congress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Congressional Reaction to Navy Report . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Issues for Congress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Electric Drive in General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Electric Drive as a Technology Area . . . . . . . . . . . . . . . . . . . . . . . . . 38

Near-Term Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Measuring and Assessing Cost Effectiveness . . . . . . . . . . . . . . . . . . 39

Technical Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Common System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Other (Non-Motor) Components . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Application of Electric Drive to Specific Ship-Acquisition Programs . . . . 54

DD-21 Land-Attack Destroyers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Virginia (SSN-774) Class Submarines . . . . . . . . . . . . . . . . . . . . . . . 58

TADC(X) Auxiliary Dry Cargo Ships . . . . . . . . . . . . . . . . . . . . . . . . 59

Jcc(x) Joint Command and Control Ships . . . . . . . . . . . . . . . . . . . . . 60

LHA Replacement Ships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

CVN(X) Aircraft Carrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Coast Guard Deepwater Cutters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Electric Drive Propulsion for U.S. Navy Ships:

Background and Issues for Congress

Introduction and Key Findings

Introduction

This report provides background information and discusses issues for Congress

regarding the use of electric-drive propulsion technology (as opposed to traditional

mechanical-drive technology) on U.S. Navy ships. As a result of technological

developments over the last few years, electric-drive technology has matured to the

point where the Navy has selected it for use on its planned next-generation DD-21

land-attack destroyer and is considering it for use on other kinds of Navy ships as

well.

Electric-drive technology would change the way that U.S. Navy ships transmit

power from their engines to their propellers, as well as the way that they manage and

distribute electrical power to both propulsion and non-propulsion systems. (Electric

drive would not require the ship’s engines to be changed; ships could continue to be

powered by diesel engines, gas turbines, or steam turbines.) The Navy’s decision to

use electric-drive propulsion technology represents a technological shift for the Navy

arguably comparable in significance to the Navy's shift from sail to steam power in the

latter 1800s or the Navy's development of nuclear propulsion in the 1950s.

Electric-drive technology is being pursued by several foreign navies, most

notably in Europe, and is being incorporated into numerous commercial ships,

especially cruise ships. Electric-drive propulsion, particularly when installed as part

of a ship-wide integrated electrical power system, could generate substantial capability

and life-cycle cost benefits for U.S. Navy ships. Electric-drive technology, however,

still requires development work, and integrating it into nearer-term U.S. Navy shipacquisition programs, particularly the DD-21 program, involves a degree of technical

risk.

The debate over whether, when, and how to incorporate electric-drive

technology into Navy ship-acquisition programs has developed rapidly over the last

three years. Key developments over this period include the following:

CRS-2

! In 1997, the Naval Studies Board of the National Research Council included

a substantial discussion of electric-drive technology in a major 9-volume report

on key technologies for the Navy and Marine Corps for the period 2000-2035.1

! In 1998, U.S. firms involved in developing electric-drive technologies began

to intensify their efforts and publicize them to both policymakers and the two

shipyard-led industry teams that are competing for the right to design the DD21 destroyer. These teams began to more intensively explore the potential for

equipping the DD-21 with electric drive.

! In June 1998, the Senate Appropriations Committee directed the Secretary of

the Navy to provide a report to the committee on the idea of a common

electric-drive system for the DD-21 and later ships in the Virginia (SSN-774)

class attack submarine program.

! In March 1999, the Navy delivered the report to Congress. The report stated

that developing common electric-drive components is feasible for several kinds

of Navy ships and that pursuing electric drive technology in the form of a

common family of components could have advantages for the Navy.

! In May 1999, the Navy completed and began testing its full-scale, land-based

electric-drive demonstration system in Philadelphia.

! In January 2000, the Navy announced that the DD-21 class would be equipped

with electric drive and that proposed funding for development of electric-drive

technology was being increased by about $250 million over the period

FY2001-FY2005.2

Electric-drive propulsion poses a number of issues for Congress concerning its

potential costs, benefits and risks, and how the technology should be integrated into

the DD-21 program or other ship-acquisition programs. Although Congress has

approved funding for Navy research and development work on electric-drive in prior

years, the Navy’s plan to expand the scope of its electric-drive development effort and

apply electric drive to at least one new class of Navy ships may require Congress in

coming years to make significant decisions relating to the technology. The decisions

1

National Research Council. Naval Studies Board. Technology for the United States

Navy and Marine Corps, 2000-2035, Becoming a 21st-Century Force. Washington, National

Academy Press, 1997. Volume 2 (Technology), p. 16, 233-281, and Volume 6 (Platforms),

p. 19-22, 105-107.

2

For coverage of the Navy’s January 2000 announcement, see Walsh, Edward J. A

Fundamental Change of Direction. Sea Power, March 2000: 24-25; Brown, David. Electric

Plant to Power DD-21 Destroyer. Navy Times, January 17, 2000: 10; Seigle, Greg. USN

Decision on Electric Drive Means More Delays. Jane’s Defence Weekly, January 12, 2000:

3; Castelli, Christopher J. Navy To Make DD-21 First Electric Drive Surface Combatant.

Inside the Navy, January 10, 2000: 2; Suro, Roberto. Navy Plans High-Powered New

Destroyer. Washington Post, January 7, 2000: A3; Department of Defense News Release

007-00, January 6, 2000, entitled Integrated Power Systems, Electric Drive Selected for New

Navy Destroyers.

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that Congress reaches could have a profound affect on future Navy capabilities, Navy

research and development funding requirements, and the U.S. marine propulsion

technological and industrial base.

Congressional Request. This report is the result of a January 31, 1999 request

to CRS from Senator Trent Lott for analysis and conclusions concerning electric

drive. Senator Lott requested that the study examine the application of electric drive

to civilian cruise ships, commercial cargo ships, surface combatants, submarines and

aircraft carriers. The request stated that the report not be limited to U.S.

developments.3

Sources of Information. In response to Senator Lott's request, CRS in March

1999 circulated a 5-page list of questions on electric drive to Navy offices, the

Defense Advanced Research Projects Agency (DARPA), the National Academy of

Sciences, U.S. shipbuilding firms, firms involved in the development of electric-drive

technology, and other organizations. Recipients were invited to respond in writing

to any or all of the questions, as appropriate, to supplement their written responses

with in-person briefings if they so desired, and to distribute the list of questions to

other potentially interested parties.

Written responses, some quite extensive, were received in March and April 1999

from the U.S. Navy, the United Kingdom’s Royal Navy, numerous industry sources,

and additional respondents. Respondents included most of the parties to whom the

list of questions was originally sent by CRS, plus additional parties that received the

list of questions indirectly. Several respondents supplemented their written responses

with in-person briefings, some quite extensive. After reviewing these materials, CRS

posed some specific follow-on questions to some of the respondents to help clarify

or elaborate certain points; these inquiries resulted in some additional written

responses and telephone conversations.

These written responses, in-person briefings, and telephone conversations

constitute the primary sources of information for this report. These sources were

supplemented with additional file materials that CRS has collected on the topic since

the late 1980s, when CRS began to track developments relating to electric-drive

propulsion for Navy ships.

Key Findings

The key findings of the report are presented below. They can be divided into

two groups: findings relating to electric-drive technology in general, and findings

relating to the potential application of electric drive to specific U.S. ship-acquisition

programs.

3

Letter from Senator Trent Lott to Congressional Research Service, January 31, 1999.

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Electric Drive in General.4

Current Status of Electric Drive. Several foreign countries, particularly in

Europe, have developed, are developing, or are using electric-drive technology in

commercial ships, naval ships, or both. Much of the development work is

government-financed. The British Navy’s electric-drive program is particularly

significant. The electric-drive systems used today in cruise ships and other

commercial ships are generally made overseas, primarily in Europe. The three

primary European-based electric-drive suppliers are Alstom (previously known as

Cegelec), Asea Brown Bovieri (ABB), and Siemens.

Electric-drive technology is used on a few U.S. government ships and is being

developed in the United States by both the U.S. Navy and private industry. The

Navy’s effort centers on the Integrated Power System (IPS) program, which was

established in 1995. As mentioned above, the IPS program recently completed

construction of a full-scale, land-based electric-drive demonstration system. Testing

of this system, located in Philadelphia, began in May 1999. The Navy’s prime

contractor for this system is Lockheed Martin, but much of the actual equipment was

provided by Alstom. Several other firms are also involved. The Navy is proposing

a total of more than $300 million for research and development on electric drive

during the period FY2001-FY2005.

Several private-sector firms in the United States are now pursuing electric-drive

technology for the U.S. Navy market. At least three private-sector entities are

offering complete electric-drive systems to the Navy:

! Alstom, which has marine operations in Britain, France, Germany, and the

United States (in Pittsburgh and Philadelphia). The company supplies electricdrive systems featuring synchronous motors and is also developing systems

featuring induction and permanent magnet motors.

! an industry team led by General Dynamics Corporation, a leading designer

and builder of U.S. Navy ships. This team is developing an electric-drive

system featuring a permanent magnet motor.5

! an industry team led by Newport News Shipbuilding (NNS), another leading

designer and builder of U.S. Navy ships. This team is also developing an

electric-drive system featuring a permanent magnet motor.

In addition to these three entities, other U.S. firms are also involved in

developing electric-drive technologies or components. These include, among others:

4

A basic description of electric-drive (as opposed to mechanical-drive) technology can

be found in the background section of this report.

5

As discussed in the background section of the report, five kinds of electric motors are

discussed in connection with electric-drive technology for ships – synchronous motors,

induction motors, permanent magnet motors, superconducting synchronous motors, and

superconducting homopolar motors.

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! American Superconductor, which is developing a superconducting

synchronous motor, and

! General Atomics, which is developing a superconducting homopolar motor

that was previously under development for many years by the U.S. Navy.

Anticipated Benefits and Disadvantages. Electric-drive technology offers

significant anticipated benefits for U.S. Navy ships in terms of reducing ship life-cycle

cost, increasing ship stealthiness, payload, survivability, and power available for nonpropulsion uses, and taking advantage of a strong electrical-power technological and

industrial base. Electric drive has potential disadvantages in terms of higher near-term

costs, increased program risk, increased system complexity, and less efficiency in fullpower operations.

Electric Drive as a Technology Area.

Although electric drive is often

discussed as a specific system that could be available in the near future for the DD-21

program, many elements of electric-drive technology have the potential to evolve and

improve over time. This suggests that policymakers might consider addressing

electric drive as not simply a proposal for a specific system that might require a few

nearer-term acquisition decisions, but as a broader technology area that might require

longer-term management and oversight and a series of research, development, and

procurement decisions stretching over the course of several years. If conducting

longer-term management and oversight of electric drive is considered appropriate, it

might be assisted by developing an electric-drive technology development roadmap

or master plan extending perhaps 10 to 25 years into the future.

Near-Term Costs. Pursuing electric-drive will incur higher near-term costs than

a strategy that places continued emphasis on mechanical-drive technology.

Developing electric-drive technology for warships would require hundreds of millions

of dollars in research and development funding in coming years, particularly if the

technology is developed for submarines as well as surface ships, and if development

of more advanced electric-drive technologies is pursued. Several (but not all) sources

for this report stated that electric-drive systems initially would be more expensive to

procure than mechanical-drive systems. The cost premium for a commercial electricdrive system (which might be suitable for use in Navy auxiliary ships) could be less.

These sources, however, agreed that the procurement cost of electric-drive systems

would come down over time, and that the higher initial costs of electric-drive systems

would be more than offset over the longer run by reduced ship life-cycle operating

and support costs.

Measuring and Assessing Cost Effectiveness. Several sources agreed that the

cost-effectiveness of electric drive should be examined not by focusing on the electricdrive system or any of its components in isolation, but rather by examining the effect

that electric drive has on overall ship cost and capability. In an expanded version of

this perspective, the cost-effectiveness of electric drive might also be measured in

terms of its effect on total fleet costs and capabilities. Estimates of the costs and

benefits of electric-drive technology should arguably include measures that examine

not just shorter- but also longer-term (i.e., life-cycle or total ownership) costs and

warfighting effects.

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Although electric-drive technology offers numerous potential cost and

warfighting benefits for Navy ships, relatively few precise estimates are available on

the magnitude of these benefits. If not redressed, the scarcity of precise and

systematic estimates will make it difficult for policymakers to assess with any

precision the potential cost-effectiveness of electric-drive technology in general and

(probably more significant) the relative cost-effectiveness of differing technical

approaches to achieving electric drive.

The Navy’s interest in electric-drive technology is consistent with the decisions

of commercial ship operators (especially cruise ship operators) and other navies in

recent years to move to electric-drive technology for their own ships. The strong

interest in electric drive by other navies (particularly the British Navy) suggests that

electric drive offers a variety of warfighting and life-cycle cost advantages for naval

ships. The interest shown by other navies in electric drive, however, also

demonstrates that there are multiple technical approaches to electric drive that should

be assessed.

Technical Risk. Incorporating electric-drive technology into Navy shipacquisition programs could add technical or schedule risk to those programs. The

potential amount of risk varies, depending on the exact configuration of the system

in question. More advanced approaches to electric drive present greater potential

technical or schedule risk, but also promise greater potential cost effectiveness.

Electric-drive components presenting potential technical or schedule risk include

motor drives, motors, generators, the electrical distribution system, advanced

propeller/stern configurations, and overall system design and integration. Issues to

be addressed include demonstrating at full scale technologies that to date have been

demonstrated at partial scale, improving thermal performance, achieving desired levels

of acoustic quieting and shock resistance, and designing overall system interfaces,

controls, and module specifications.

Some of the risks involved in developing electric-drive technology have been

mitigated by the successful development of electric-drive technology for commercial

ships. Some industry sources argue that the amount of remaining risk involved in

developing electric drive for Navy use is low to moderate. Other sources suggest that

the degree of risk may be higher, particularly if the technology is developed on an

aggressive schedule. Technical risk involved in developing electric drive might be

mitigated through more intensified research and development.

Common System. The Navy stated in its March 1999 report to Congress that

developing common electric-drive components is feasible for several kinds of Navy

ships and that pursuing electric drive technology in the form of a common family of

components could have advantages for the Navy. The Navy and the other military

services have used commonality in numerous acquisition programs over the years, and

Navy leaders are now placing increased emphasis on the concept.

Potential advantages of a common electric-drive system (or a family of common

components) include nearer-term cost savings due to streamlining of research and

development costs, both nearer- and longer-term savings due to greater efficiencies

in procurement, and longer-term savings due to the streamlining of fleet training,

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operation, and support efforts. Potential savings are difficult to estimate, but could

be substantial.

The concept of developing a common system or family of components poses

issues for policymakers concerning the extent of commonality across electric-driveequipped Navy ships and the use of competition in the development and procurement

of electric-drive technology. Past acquisition experience clearly suggests that

designing a unique electric-drive system for each kind of ship would not result in the

most cost-effective application of electric drive across the fleet. Past experience,

however, does not prove conclusively that it would be achieved by an approach that

would install a common system or family of components on every kind of ship that is

scheduled to be powered by electric drive. Commonality is not an end in itself but

rather would be a strategy for policymakers to consider in seeking the most costeffective path to apply electric-drive technology across the fleet. Policymakers might

wish to assess the relative merits of both a maximally common approach and more

mixed approaches that combine elements of commonality with elements of shipspecific solutions.

Pursuing a common electric-drive system or family of components could in

theory lead to the emergence of a dominant or monopoly supplier to the Navy of

electric-drive technology, components, and systems. In light of this possibility,

policymakers who place a high value on the use of competition in defense

development and procurement might consider taking actions aimed at ensuring that

any Navy acquisition strategy for electric drive makes maximum use of competition

between competing industry approaches prior to selecting the approach that would

form the basis for the common system. From this perspective, it may also be

appropriate to aim at ensuring that nearer-term acquisition decisions preserve, as

much as possible, a potential for employing competition in the eventual development

and procurement of follow-on electric-drive technologies, components, and systems.

One possible approach would be to require the common electric-drive system to be

designed to a so-called open architecture. Another possible approach would be to

provide continuing funding to firms other than those who supply the current electricdrive system to finance continued development of potential competing technologies

or components.

Motors. Much of the debate since 1998 over the application of electric-drive

technology to U.S. Navy ships concerns the type of electric motor that should be

used. The issue is highly charged because specific motor types are associated with

specific firms competing for a part of the Navy’s prospective electric-drive program.

The electric motors associated with electric-drive systems for large ships can be

divided into five basic categories – synchronous motors, induction motors, permanent

magnet motors, superconducting synchronous motors, and superconducting

homopolar motors.

The synchronous motor can be considered the most mature technologically in

application to large ships. There is a consensus among both naval and industry

sources that the synchronous motor, if scaled up to the higher horsepower ratings

needed to move surface combatants and submarines at high speeds (i.e., 30+ knots),

would be too large and heavy to be suitable for use on these ships. The most likely

apparent opportunity for incorporating electric-drive systems using synchronous

CRS-8

motors (presumably commercially available systems) into the Navy’s electric-drive

effort would be to install them in large Navy auxiliary ships.

The induction motor is generally considered the second-most mature motor type

for application to large ships, after the synchronous motor. It is the type of motor

used in the Navy’s full-scale, land-based electric-drive demonstration system. Most

of the sources consulted for this report argue (or do not contest) that it can be

sufficiently power-dense to be suitable for use on U.S. Navy surface combatants. By

the same token, however, most sources – including the U.S. Navy in its March 1999

report to Congress – also argue (or do not contest) that the induction motor is not

sufficiently compact or quiet to be suitable for use on U.S. Navy submarines. Using

an electric-drive system with an induction motor (rather than the currently less mature

permanent magnet motor) might help mitigate the risk of integrating electric-drive

technology into the DD-21 program, but would preclude achieving motor

commonality across surface ships and submarines.

The permanent magnet motor can be made quieter and significantly more powerdense than the induction motor – enough so that it is consequently considered suitable

for use on submarines as well as surface combatants. Sources generally agree that the

permanent magnet motor can be used in a common electric drive system for Navy

surface ships and submarines. The Navy’s March 1999 report to Congress focuses

on the permanent magnet motor as the motor available in the nearer term that would

be suitable for a common electric-drive system.

The permanent magnet motor is less mature technologically than the induction

motor, and consequently at this point may pose more development risk to incorporate

into a nearer-term ship-acquisition program such as the DD-21 destroyer. Sources

differ regarding the amount of technical risk involved in scaling up the permanent

magnet motor to full size. Some argue that the basic technological issues in

permanent magnet motors have been resolved, and that scaling up the technology will

not pose any new issues; others demur, arguing that scaling up is never risk-free. The

Navy’s decision, announced in February 2000, to delay the procurement of the first

DD-21 by one year (to FY2005) will, other things held equal, reduce the risk

associated with equipping the first DD-21 with an electric-drive system using a

permanent magnet motor.

The superconducting synchronous motor, if successfully developed, could be

more power-dense and quieter than a permanent magnet motor. The superconducting

synchronous motor is less mature technologically than the permanent magnet motor

and was not discussed in the Navy’s March 1999 report. Most sources argue (or do

not contest) that it cannot be matured quickly enough to be installed at acceptable risk

on the first DD-21. Advocates of the superconducting synchronous motor, while not

necessarily disagreeing, argue that the technology for this kind of motor has

progressed in recent years and that the time needed to mature the technology may be

less than others estimate. The firm developing this motor says that, with adequate

funding, it could be developed and completed by 2009, making it possible to have the

motor enter service with the fleet in 2012.

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The superconducting homopolar motor,6 if successfully developed, could

similarly be more power-dense and quieter than a permanent magnet motor. The Navy

worked on developing the homopolar motor for many years starting in the mid-1970s.

The homopolar motor, like the superconducting synchronous motor, is less mature

technologically than the permanent magnet motor and was given little emphasis in the

Navy’s March 1999 report. Advocates of this motor, like those of the

superconducting synchronous motor, argue that the technology for this kind of motor

has progressed in recent years and that the time needed to mature the technology may

be less than others estimate. The firm now developing this type of motor says that,

with adequate funding, it could be developed and completed in 5 or 6 years.

Other (Non-Motor) Components. There is considerable potential for evolution

and improvement in the non-motor elements of electric-drive technology. This is

potentially significant, because with the partial exception of the motor drive, there has

been relatively little discussion of how these other components could or should evolve

or be improved.

Application of Electric Drive to Specific Ship-Acquisition Programs.

DD-21 Land-Attack Destroyers. Given the possibility that the DD-21's system

might become the basis for a common electric-drive system for the Navy, the

economic stakes for firms competing to build the system are potentially very high.

The Navy’s acquisition strategy for the DD-21 program gives the two industry teams

that are competing for the right to design the DD-21 wide latitude in selecting the

type of electric-drive system the ship would use. This approach is consistent with

Navy and Department of Defense acquisition reform efforts.

The potential for the DD-21's electric-drive system to become the basis of a

common electric-drive system, together with the Navy’s acquisition strategy for the

program, raise several potential issues for Congress. These issues concern: the DD21 program schedule and its effect on the technical risk in developing electric drive;

the adequacy of DD-21 program funding for development of electric drive; the

achievability of the DD-21 ship procurement cost goal; the potential for evolving the

DD-21's electric drive system over time; the appropriateness of the latitude given to

the two DD-21 industry teams in determining the ship’s propulsion system; and how

to reconcile the potentially conflicting goals of optimizing electric drive for DD-21

and optimizing it for application to multiple Navy ship types.

Given the competing motor technologies now being pursued, there are numerous

potential strategies that can be pursued concerning the type of motor used in the DD21 electric-drive system. Sources differed regarding the amount of technical risk

associated with incorporating different versions of an electric-drive system into the

first DD-21. The lowest-risk option would appear to be a system using an induction

motor connected by a traditional horizontal shaft at the stern of the ship to a fixed-

6

The term homopolar (i.e., unipolar) refers to the fact that this motor uses direct current

(rather than alternating current) electricity and does not require either a reversal of current or

electrical commutation. As a result, the magnetic field and the electrical current in the

armature of a homopolar motor are constant over time and space (i.e., unvarying).

CRS-10

pitch propeller. With some added risk, the lead ship’s system could include a

permanent magnet motor rather than an induction motor. Eventually, an advanced

propeller/stern configuration such as a podded propeller7 could be developed for the

DD-21.

On June 14, 2000, Ingalls Shipbuilding, the leader of one of the two industry

teams competing for the DD-21, announced that it had selected the NNS-led electric

drive industry team for the preliminary design of an electric drive propulsion system

and will incorporate the NNS-led team’s permanent magnet motor design into its

initial system design proposal for the DD-21.

Virginia (SSN-774) Class Submarines. Electric-drive technology in some form

could be installed on follow-on Virginia-class submarines. Navy officials testified in

June 2000 that a nearer-term electric-drive system could be ready for a Virginia-class

boat procured in FY2010. Some industry sources suggested that it could be ready for

a boat procured in FY2007 if a decision were made in the near term to pursue the

option and adequate development funding was provided.

Some industry sources have suggested, and the Navy did not disagree, that

electric-drive technology for submarines, if pursued ambitiously, has the potential for

altering the stern of a Virginia-class submarine in a way that could reduce the

procurement cost of the submarine (currently $1.9 billion to $2.0 billion) by as much

as $100 million. Pursuing electric-drive technology for submarines this ambitiously,

however, would be very expensive: It could easily require hundreds of millions of

dollars, or even more than a billion dollars, in research and development funding

beyond the funding that the Navy has already programmed for development of

electric-drive technology.

TADC(X) Auxiliary Dry Cargo Ships. The Navy’s planned TADC(X) class of

auxiliary dry cargo ships, the first of which was procured in FY2000, is a near-term

candidate for electric-drive propulsion. As a large, slower-speed, non-combat ship

now in procurement that is somewhat similar to a commercial cargo ship, it might be

feasible and cost-effective to equip the TADC(X) with a currently available European

commercial electric-drive system similar to those now being used for cruise ships.

JCC(X) Joint Command and Control Ships. Electric drive might similarly be

a candidate for the joint command and control (JCC[X]) ships that the Navy plans to

begin procuring in FY2004. If these ships are built to commercial-ship standards, the

JCC(X) might be a candidate for a commercial electric-drive system. The operational

requirements of the JCC(X), however, might require a Navy-developed electric-drive

system with better quieting and shock resistance.

LHA Replacement Ships. LHD-8 – a modified Wasp (LHD-1) class ship that

will be the first LHA replacement ship – is to be equipped with a hybrid propulsion

plant consisting of a low-power electric-drive system for low-speed operations and

a mechanical-drive system for higher-speed operations. The Navy is now assessing

7

See figure 3 in the background section (page 18) for an illustration of a podded

propeller.

CRS-11

whether the second through fifth LHA replacement ships should be additional (and

further-modified) LHD-1 class ships or a new-design amphibious assault ship known

as the LHX. The further-modified-LHD option might, and the LHX option more

certainly could, include a full electric-drive system.

CVN(X) Aircraft Carrier. The Navy’s March 1999 report to Congress on

electric drive states that while electric drive is feasible for future aircraft carriers,

mechanical drive would be more appropriate for CVN(X)-1, the first of the Navy’s

planned class of next-generation aircraft carriers, which is to be procured in FY2006.

The Navy’s conclusion contrasts with a 1997 Naval Research Advisory Committee

(NRAC) report on the CVN(X) that strongly endorsed equipping the CVN(X) with

electric-drive technology. Policymakers may review the Navy’s 1999 conclusion

periodically (e.g., with the procurement of each carrier) to determine whether it

remains valid.

Coast Guard Deepwater Cutters. The 1998 Navy-Coast Guard national fleet

concept, with its emphasis on commonality, raises the possibility of using electricdrive on the new cutters that are to be procured under the Coast Guard Deepwater

project. Equipping these cutters with electric-drive could produce ship capability and

life-cycle cost benefits for the Coast Guard similar to those that electric-drive

technology is expected to produce for the Navy, and potentially improve economies

of scale for both the Navy and Coast Guard in the production, operation, and lifecycle support of ship propulsion systems. Incorporating electric drive into the

Deepwater program, however, would pose several significant issues in terms of

feasability, cost, and program disruption, particularly since the first cutter is to be

procured in 2002 and competing Deepwater industry teams have already completed

much of their design work for the ship.

Background

Basic Description of Electric Drive

Electric vs. Mechanical Drive. A ship's drive system is the equipment that

transmits power from the ship's engines to its propellers. It is roughly analogous to

the transmission and drive shaft in a car, which transmit power from the car's engine

to its wheels.

Most of the world's larger civilian and military ships today use a mechanicaldrive system. In very simplified form, with a mechanical-drive system, the higherspeed revolutions per minute (RPMs) produced by a ship's engine (also known as the

prime mover) are transmitted by a rigid shaft to a set of gears, known as reduction

gears, that convert (i.e., reduce) these higher-speed RPMs to the lower-speed RPMs

that are more appropriate for a larger ship's propeller. A second rigid shaft then

transmits these lower-speed RPMs from the reduction gears to the propeller. Ships

with multiple propellers have multiple engines, reduction gears, and sets of shafts.

With an electric-drive system, in contrast, a generator converts the engine's

higher-speed RPMs into electricity. This electricity is then transmitted by an electrical

CRS-12

cable toward the stern of the ship, to a device called a motor drive or motor

controller, which modifies the voltage and frequency of the electricity as needed for

the ship's electric motor to operate properly and at the desired speed. The electric

motor then converts the electricity into lower-speed RPMs that turn the propeller.

Ships with multiple propellers have multiple electric motors and motor drives.

Figure 1 depicts the basic arrangements of mechanical- and electric-drive

systems.

Integrated Electric Drive (Integrated Power System). Ships with mechanicaldrive systems actually have two sets of engines. One set is used for ship propulsion,

as described above. A second and separate set, connected to electrical generators, is

used to generate electricity for all of the electrically powered equipment on the ship.

A U.S. Navy Arleigh Burke (DDG-51) class destroyer, for example, has a set of four

large gas-powered turbine engines for propulsion, and a second set of three smaller

gas turbines that produce electrical power for the ship.

In a ship with a mechanical-drive system, the power-producing capability of the

ship's propulsion engines typically represents 75 percent to 85 percent of the ship's

total power-producing capability. This power-producing capability is devoted

exclusively to ship propulsion and is not available for non-propulsion uses, even when

the ship is stationary or traveling at low speed.

Ships with an electric-drive system, in contrast, can be designed so that a single

set of engines produces a common pool of electricity that is used for both ship

propulsion and the ship's non-propulsion electrical loads. Such a system is known as

an integrated electric-drive (IED) system or integrated power system (IPS).

In ships with integrated electric drive, the electricity produced by the engines and

generators is sent by cable to an electric switchboard that divides the electricity into

two flows -- one for the ship's propulsion needs, and one for the ship's other electrical

loads. The switchboard can alter the distribution of power between these two uses

on a moment-to-moment basis, as needed, to meet the ship's propulsion and nonpropulsion needs.

With an integrated electric drive, the large amount of power needed to propel

the ship at high speeds is thus available, if needed, for other uses. Even when the ship

is traveling at high speed, power can be momentarily diverted away from the

propulsion system to a non-propulsion system that needs a short burst of highstrength power without appreciably slowing the ship down. An integrated electric

drive is roughly analogous to the arrangement in the "Star Trek" science fiction

television series, in which the captain of the star ship can order the ship's engineer to

divert power from the ship's engines to its weapons or other systems.

All current proposals for using electric drive propulsion on U.S. Navy ships

envisage an integrated electric drive system. Consequently, in this report, the term

electric drive is used to refer to integrated electric drive. Figure 1 shows the basic

arrangement of an integrated electric drive system.

CRS-13

Figure 1.

Reduction

gears

Engine

Shaft

Shaft

Propeller

Basic mechanical-drive system

(not to scale)

Engine

Generator

Cable

Motor

drive

Motor

Cable

Shaft

Short shaft

Basic electric-drive system

(not to scale)

Propeller

CRS-14

Key Components. As shown in Figure 2, an integrated electric drive system

includes the following major elements:

! Engines (also known as prime movers). On U.S. Navy surface combatants,

the engines are gas turbines (modified versions of jet engines used on

commercial airliners) that burn jet fuel. On U.S. Navy submarines and most

U.S. Navy aircraft carriers, the engines are steam turbines whose steam is

created using heat produced by a nuclear reactor. On other ships (particularly

those with lower maximum speeds), the prime movers can be diesel engines.

! Generators, which convert the mechanical energy produced by the engines –

higher-speed RPMs – into electricity.

! Electric switchboard, which distributes the electricity to propulsion and nonpropulsion needs.

! Motor drives (also known as motor controllers), which modify the voltage

and frequency of the electricity as needed for the ship's electric propulsion

motors to operate properly and at the desired speed.

! Motors, which convert electrical power from the motor drives to lower-speed

RPMs suitable for a large ship's propellers.

! Propellers, which use the lower-speed RPMs to propel the ship through the

water.

! Non-propulsion power distribution system, which distributes the remaining

electrical power to the various non-propulsion electrical loads around the ship.

This system includes additional cables, switches and power-conversion devices.

Common Electric Drive System. Over the last year or two, the terms

"common electric drive" and "common integrated electric drive" have come into use

to refer to an electric drive system that is designed with common components that can

be installed on various types of Navy ships (e.g., submarines, surface combatants,

amphibious ships, and auxiliary ships).

All-Electric Ship. On some ships today, some auxiliary systems are either

steam-powered (e.g., space heaters, laundry equipment, and galley [kitchen]

equipment), hydraulically (fluid) powered (e.g., steering systems and submarine diving

systems), or pneumatically (air) powered (e.g., valve actuators and surface-ship

turbine engine starters). On an integrated electric drive ship, converting these

remaining non-electrical systems to electrical power would produce what is known

as an all-electric ship. Some observers view the all-electric ship as a natural

progression from an integrated electric drive ship.

CRS-15

Figure 2.

Engine

Generator

M otor

drive

Sw itchboard

Cable

M otor

Cable

Short shaft

Cable

Electrical power

for non-pro pulsion

electrical loads

Basic integrated electric-drive system

(not to scale)

Shaft

Propeller

CRS-16

Motor Types. A key element in discussions of electric drive concerns the type

of motor to be used. The motor types associated with electric-drive systems for large

ships can be organized into the five general categories shown in the table below. They

all convert electrical energy into mechanical energy (RPMs). They differ, however,

in certain key characteristics, including the type of electrical current used – alternating

current (AC) or direct current (DC) – the source of the magnetic field that is

combined with the flow of electrical energy to create mechanical energy; and whether

the motors conduct the electrical energy using use conventional electrical wires or

superconducting wires and associated technology.

Table 1. Basic Motor Types for Large-Ship Electric-Drive Systems

Long Name

Short Name

AC wound-field synchronous motor

Synchronous motor

AC induction (asynchronous) motor

Induction motor

AC permanent magnet synchronous motor

Permanent magnet motor

AC superconducting synchronous motor

Superconducting synchronous motor

DC superconducting homopolar motor

Homopolar motor

In addition, it should be noted that three versions of the permanent magnet

motor have been discussed in connection with electric-drive systems for ships – the

radial-gap (radial-flux) version, the axial-gap (axial- flux) version, and the transverseflux version. These versions differ in the design and orientation of their fixed and

rotating elements (their stators and rotors) and consequently in how electromagnetic

lines of flux in the motors work to create mechanical movement. In short, a radialgap motor can be described as a cylinder rotating within another cylinder; the axialgap motor can be described as a disk spinning between two other disks, and the

transverse-flux motor can be described as a rimmed disk whose rim spins inside

slotted rings.

Anticipated Benefits and Potential Disadvantages

Anticipated Benefits.8 Electric-drive technology offers significant anticipated

benefits for U.S. Navy ships in terms of reducing ship life-cycle cost, increasing ship

stealthiness, payload, survivability, and power available for non-propulsion uses, and

taking advantage of a strong electrical-power technological and industrial base.

Reduced Ship Life-Cycle Cost. Depending on the kind of ship in question and

its operating profile (the amount of time that the ship spends traveling at various

speeds), a Navy ship with an integrated electric-drive system may consume 10 percent

8

For examples of articles discussing the benefits of electric drive, see McCoy, Timothy

J. Powering the 21st Century Fleet. U.S. Naval Institute Proceedings, May 2000: 54-58;

Leonard, Robert E, and Thomas B. Dade. The All Electric Ship: Enabling Revolutionary

Changes in Naval Warfare. Submarine Review, October 1998: 43-53.

CRS-17

to 25 percent less fuel than a similar ship with a mechanical-drive system. The Navy

estimates a savings of 15 to 19 percent for a ship like a surface combatant.

In addition, electric drive makes possible the use of new propeller/stern

configurations, such as a podded propulsor (see Figure 3), that can reduce ship fuel

consumption further due to their improved hydrodynamic efficiency. Estimates of

additional savings range from 4 percent to 15 percent, depending on the ship type and

the exact propeller/stern configuration used.9

For fossil-fueled ships, fuel consumption is a major contributor to annual ship

operating and support costs. Over the life of the ship, the savings from reduced fuel

consumption promise to significantly outweigh the potential increase in initial

procurement cost associated with electric drive, thus significantly reducing the ship's

total life-cycle cost, also known as total ownership cost (TOC). The Navy is now

placing increased emphasis on life-cycle cost in the acquisition process so as to more

effectively capture the long-term cost consequences of its acquisition decisions.

In addition to savings on fuel, it is anticipated that electric-drive systems may

require less maintenance and fewer crew members to operate than mechanical-drive

systems. Electric-drive systems can be designed to be highly automated and selfmonitoring. Reductions in maintenance and crew size would further reduce ship lifecycle cost.

Increased Stealth. Electric drive promises to be significantly quieter acoustically

than mechanical drive. Since acoustic noise is an important component of a ship's

overall detectability, ships equipped with electric drive promise to be less detectible

(i.e., more stealthy) than ships equipped with mechanical-drive technology.

9

A podded propulsor is a streamlined, roughly cylindrical pod with a propeller attached

to one end (usually the front end) that is suspended from the bottom of the ship. The pod,

which contains the electric motor driving the propeller, can be designed to swivel in a circle

so as to direct the propeller’s thrust in any direction and thereby steer the ship. A podded

propulsor eliminates the need at the stern of the ship for a lengthy, exposed horizontal shaft

leading to the propeller and a rudder for steering the ship. With a podded propulsor, there are

fewer exposed components to create drag (i.e., resistance to forward movement), and the

propeller encounters a more uniform (i.e., less disturbed) water flow, increasing its efficiency

(i.e., its ability to use its RPMs to create thrust). Using podded propulsors can improve a

ship’s maneuverability by permitting a tighter turning radius and by giving it the ability to

change the ship’s direction of movement or its orientation even at very low speeds. A podded

propulsor might also offer certain advantages in terms of maintenance and repair, since the

pod can be detached and quickly repaired or replaced by a like unit without need for cutting

an opening into the ship’s hull and working around other equipment. For an article discussing

podded propulsion systems, see Bonner, Kit. Naval Propulsion for the 21st Century: The

Azipod System. U.S. Naval Institute Proceedings, August 1999: 74-76.

CRS-18

Figure 3.

Conventional propeller/stern arrangement with horizontal shaft,strut, propeller, and rudder

(not to scale)

Motor

Potential revised propeller/stern arrangement with rotating podded propulsor and no rudder

(not to scale)

CRS-19

The significantly improved quieting promised by electric drive may be the single

most important benefit of electric drive to the Navy's submarine community.

Stealthiness is fundamental to a submarine's survivability and effectiveness and

acoustic noise remains the most reliable method by which submarines can be detected

and tracked at longer ranges. The Navy has expended significant resources over the

last few decades on making its submarines increasingly quiet (so as to stay ahead of

increasingly capable adversary submarine-detection equipment), and has stated that

electric drive is needed to provide the next significant improvement in acoustic

quieting on submarines.10

Although traditionally not as critical for surface warships, stealthiness –

including acoustic quieting – is becoming increasingly important as a contributor to

surface warship survivability and effectiveness. The improved acoustic quieting

promised by electric drive thus promises to be of benefit to surface ships as well. In

addition, electric-drive, by permitting a reduction in the volume devoted to air intakes

and exhaust ducts, can reduce a surface ship’s infrared signature and radar cross

section. New propeller/stern configurations made possible by electric drive might

reduce the wake signature of surface ships, which could reduce their detectability by

remote overhead sensors and improve their chances of defeating much-feared wakehoming torpedoes.

Increased Payload. In a surface combatant, electric drive's reduced fuel

consumption can translate into a reduction in the amount of space aboard ship

required for fuel storage.11 In addition, by eliminating the so-called "tyranny of the

shaft line" -- the need, in a mechanical drive system, to install the engines, reduction

gears, shafts, and propellers in a long line running along the bottom of the ship -electric drive makes it possible to install the various parts of a surface combatant's

drive system in positions that may use space aboard ship in a more efficient manner.

For example, it may permit the ship's turbine engines to be located higher in the ship,

reducing the amount of interior space required for the ducts that are needed to take

air down into the engines and to carry exhaust gases away from the engine.

In both these ways, electric drive may free up space aboard the ship that can be

used to carry additional payload (e.g., weapons or sensors). Freed-up space can also

be used for other purposes, such as increasing the size of staterooms for members of

the ship’s crew so as to improve their quality of life aboard ship – an objective which

has recently emerged as a Navy priority.

Increased Survivability. Electric-drive can improve ship survivability in several

ways. Eliminating mechanical drive's tyranny of the shaft line can improve ship

survivability by eliminating the possibility that one or more of the ship's long shaft

lines will be thrown out of alignment and rendered useless by a nearby weapon

explosion. Eliminating the requirement to locate elements of the ship's drive system

10

Bender, Bryan. US Navy Sets Sights on Electric Attack Submarine. Jane’s Defence

Weekly, July 26, 2000; Bowman, Frank L. “Skip.” Submarines in the New World Order.

Undersea Warfare, Spring 1999: 7.

11

Alternatively, if fuel storage capacity is held constant, electric drive can permit an

increase in ship operating endurance (range).

CRS-20

all in a straight line along the bottom of the ship makes it possible to place them in

locations where they may be better protected from attack by certain weapons (e.g.,

mines).

Electric drive makes it possible to more widely distribute elements of the

propulsion system around the ship, making it less likely that a single weapon might

disable the entire drive system. With an integrated power system, the flow of power

from distributed power sources can be rapidly reconfigured in the event of damage

to the ship to ensure a continued supply of electricity to vital systems. Past

experience with battle damage to naval ships suggests that this could be a very

significant benefit. And for surface ships, electric drive permits smaller propulsion

machinery spaces, which could facilitate damage control and permit greater use of

automated damage-control technologies.

Increased Power Available for Non-Propulsion Systems. As mentioned earlier,

electric drive makes large amounts of power available for non-propulsion uses such

as powerful radars and sonars, laser weapons, high-power microwave weapons,

electromagnetic rail guns, electrothermal guns, electromagnetic aircraft launch and

recovery systems (i.e., electromagnetic catapults and arresting wires), or rapidly

charging the batteries of unmanned air vehicles (UAVs), unmanned underwater

vehicles (UUVs), and high-energy undersea sensor networks.12 Some of these

functions, particularly the weapons, may require peak power levels measured in tens

of megawatts, and adding this much electrical-generating capacity to a mechanicaldrive ship would incur substantial additional costs.13

Strong Technological and Industrial Base. Some elements of the Navy's

current mechanical-drive systems, particularly reduction gears that have been specially

engineered for quiet operations, are generally not found in commercial application,

limiting economies of scale in their production and support. Advocates of electric

drive argue that as commercial ships shift to greater reliance on electric drive,

mechanical-drive technology will experience declining economies of scale that will not

only increase its production and support costs, but also possibly reduce the incentive

for manufacturers of mechanical-drive components to invest in further improvement

of mechanical-drive technology. In contrast, advocates of electric drive argue,

electric-drive propulsion will benefit from increasing production and support

economies of scale, and will also be able to take advantage of rapid technological

advances in the large and vibrant commercial electrical-power and electronics

industries.

Potential Disadvantages. Electric drive has potential disadvantages in terms

of higher near-term costs, increased program risk, increased system complexity, and

less efficiency in full-power operations.

12

See, for example, Bender, Bryan. US Navy Sets Sights on Electric Attack Submarine.

Jane’s Defence Weekly, July 26, 2000.

13

Electric drive in the future could also facilitate the replacement of today’s prime

movers (e.g., diesel engines, gas turbine engines, or steam turbines) and generators with more

efficient power-producing technologies, including direct energy-conversion devices such as

fuel cells.

CRS-21

Higher near-Term Costs. Pursuing electric-drive technology would incur higher

near-term development costs than a strategy that places continued emphasis on

mechanical-drive technology. Most sources also stated that electric-drive systems

would initially be more expensive to procure than mechanical-drive systems.

Increased Program Risk. Sources for this report acknowledged that

incorporating electric-drive (rather than mechanical-drive) technology into Navy shipacquisition programs could add technical or schedule risk to those programs, since

electric-drive technology is less mature than mechanical-drive technology for

application to naval ships. Areas of potential technical risk in developing electricdrive technology, depending on the approach taken, include motor drives, motors,

generators, the electrical distribution system, advanced propeller/stern configurations,

and overall system design and integration.

Increased System Complexity. Electric drive can add complexity to the ship’s

design both in the number of major elements involved in the drive train14 and in the

complexity of the ship’s electrical system. Added complexity in general can raise

potential concerns regarding issues such as overall system reliability and

maintainability. Proponents of electric drive argue that the technology has shown

itself to be highly reliable and maintainable after extensive use in cruise ships and other

commercial ships.

Less Efficiency at Full Power. Electric-drive systems can be less efficient than

mechanical-drive systems for full-power (i.e., maximum-speed) operations, due to the

energy losses involved in converting RPMs into electricity, and electricity back into

RPMs.15 Naval ships, however, typically spend only a small fraction of their time at

full power. Typically, most of their time – about 80 percent, by one estimate – is

spent at half-speed (roughly one-eighth power) or less. As a result, for naval ships,

losses due to the somewhat lower efficiency when operating at full power will likely

be more than offset by gains due to higher efficiency when operating at partial power.

Brief History of Electric Drive

Electric-drive technology dates to about 1910, following the development of the

first large electric motors and generators. At that time, electric-drive systems

(developed by the United States) and mechanical-drive systems employing reduction

gears (developed by the British) were both being perfected and competed against one

another. By the 1920s, the British developed a lightweight, high-efficiency

mechanical-drive system, and mechanical drive emerged as the predominant ship

propulsion technology. As summarized by one naval writer,

The history of electric propulsion in naval vessels began in 1912 with the US

Navy’s fleet collier Jupiter [AC-3], successfully powered by a Melville-McAlpine

turbo-electric system and prototype for future capital ship installations. In 1919,

14

Some sources disagreed with this, saying that when auxiliary systems are taken into

account, electric-drive systems can be made less complex than mechanical-drive systems.

15

This is why electric drive is viewed as not necessarily better than mechanical drive for

commercial cargo ships that sprint between ports at consistently high speeds.

CRS-22

the US Congress, still refusing funds for aircraft carrier construction as such,

made an allocation for the conversion of the Jupiter to the Navy’s first, albeit

experimental, aircraft carrier Langley (CV-1), which entered service in 1922.

Three 32,000 [shaft horsepower] New Mexico class turbine powered

[mechanical drive] battleships were ordered in 1914 but, in build [during

construction], it was decided to install a turbo-electric [i.e., electric-drive] system

in the lead ship.... While this was a heavier [drive system] installation than those

of the two sister ships, the New Mexico proved more economical, flexible, and

provided better manoeuverability. Nevertheless, during major refits over 19311933, all three ships were given new 40,000 shp [shaft horsepower] straight

turbine [mechanical drive] installation[s] for an extra 0.75 kts [knots].

In 1915, two Tennessee class [battleships], similar to the New Mexico...

were ordered. These were immediately followed by three almost identical

[Colorado-class ships], also with turbo-electric propulsion. The foregoing five

battleships were survivors of the 1922 Washington Naval Treaty under which 11

further projected electric-driven capital ships were cancelled....

Two further products of the treaty were the Lexington (CV-2) and Saratoga

(CV-3), survivors of a class of six battle cruisers ordered over 1916-1919 and on

which work was stopped on the slip. Work on the named ships restarted in 1922

to complete them as aircraft carriers, the U.S. Navy’s first real two [ships] of the

type.... During WWII, the US produced numbers of turbo-electric vessels due, to

some extent, to a shortage of [reduction] gear-cutting capacity in those years.16

16

Wood, Geoffrey. Electric Propulsion In Warships – Then and Now. Naval Forces,

No. 3, 1995: 20. Another naval analyst has written that:

a major U.S. Navy success story of the early part of [the 20th] century [was] turboelectric drive for capital ships (five battleships and the battle cruisers completed

as the carriers Lexington (CV-2) and Saratoga (CV-3)).... Turbo-electric power

was abandoned only because the post-World War I naval arms treaties made it

vital to save weight; geared turbines [used in mechanical-drive systems] were far

lighter. The U.S. Navy was unique in adopting turbo-electric power for major

warships (some [cruise] liners built after World War I also were turbo electric),

probably because the pre-1914 United States had the world’s most advanced

electric power industry.

The U.S. Navy revived turbo-electric plants during World War II for destroyer

escorts, because U.S. gear-cutting capacity was insufficient. As in capital ships,

turbo-electric machinery carried a considerable cost in weight and volume. As it

turned out, however, the necessary lengthening of the ships’ hulls reduced

hydrodynamic (wave-waking) resistance enough to balance off the extra weight,

and the resulting Buckley (DE-51)- and Rudderrow (DE-224)-class escorts were

as fast as the geared turbine design would have been (which was not, in the event,

built as planned). These ships apparently proved entirely satisfactory. (Friedman,

Norman. Navy Commits to Electric Drive. U.S. Naval Institute Proceedings,

April 2000: 4, 6.)

See also Eisman, Dale. Advantage of Electric Ships Hasn’t Changed Much Since 1900's.

(continued...)

CRS-23

After World War II, mechanical-drive technology continued to be improved and

remained the dominant approach. Among warships, electric-drive technology was

widely adopted only for submarines, where the diesel-electric power plant became the

standard system because it permitted the submarine to propel itself submerged for

limited periods of time on battery power, without need for access to the atmosphere

as a source of oxygen for use in burning a fossil fuel.17

In the years after World War II, electric-drive technology was occasionally

reexamined for use on ships other than smaller diesel-electric submarines. The United

States, for example, built two one-of-a-kind nuclear-powered attack submarines to

experiment with the technology -- the Tullibee (SSN-597), which entered service in

1960 and was decommissioned in 1988, and the Glenard P. Lipscomb (SSN-685),

which entered service in 1974 and was decommissioned in 1990. Electric drive was

also used in some large commercial ships, such as the cruise ships Normandie (in

1936) and Canberra (in 1960).

These periodic experiments, however, tended to confirm that electric-drive

technology, while promising, was not competitive with modern mechanical-drive

technology for large submarines and surface ships. The Tullibee and Glenard P.

Lipscomb, for example, were significantly slower than other Navy attack submarines

due to limits on the power of their electric motors, and their drive systems were very

maintenance-intensive.18

The post-World War II dominance of mechanical drive began to be challenged

starting in the mid-1970s, when technological developments in motors and particularly

motor drives made electric drive potentially more cost-effective than mechanical drive

for larger naval ships.

With regard to motors, large warships require high-horsepower motors that are

reliable, power-dense (i.e., compact), shock-resistant, and quiet, and that deliver their

horsepower in the form of slow RPMs (suitable for slowly revolving ship propellers)

but high torque.19 High-horsepower electric motors have existed for many years, but

they tend to be high-RPM/low-torque machines rather than low-RPM/high-torque

machines. In the 1980s, moderate-horsepower, low-RPM/high-torque electric motors

were developed, but their horsepower was still not sufficient to move large warships

16

(...continued)

Virginian-Pilot, February 11, 2000.

17

In a diesel-electric submarine, a diesel engine (using air drawn down from the surface

through a snorkel) is used to generate electricity that is stored in batteries. This stored

electrical power is then drawn from the batteries to power the ship during submerged

operations.

18

See, for example, Lipscomb Exit May Have Lessons For Burke Electric Drive. Navy

News & Undersea Technology, January 29, 1990: 2.

19

Torque is the twisting power of the motor on the shaft, measured in foot pounds of

force. An everyday analogue can be found in doorknobs: a stiff or heavy doorknob requires

the hand and arm to generate more torque to operate than does a light or loose doorknob. For

motors, horsepower is the product of RPMs times torque, divided by 5252.

CRS-24

at high speeds. Only in the last several years has development work progressed on

high-horsepower, low-RPM/high-torque electric motors that are sufficiently powerdense and quiet for use on surface combatants and submarines.

With regard to motor drives, only within the last few years has it been possible

to develop devices that could handle the high amounts of electrical power associated

with high-horsepower motors and convert it efficiently into the kind of high-quality

(i.e., almost-distortion-free) power needed to ensure that an electric motor engineered

to operate quietly will in fact operate quietly.20 Developments in the last couple of

years in power electronics – semiconductor-based electronic devices that are capable

of handling large flows of power, as opposed to the much smaller flows of energy

handled by the semiconductor chips in a computer – have progressed to the point

where it is now possible to build high-capacity motor drives that can operate

efficiently and deliver very-high-quality power to high-horsepower electric motors.

The development of semiconductor-based power-conversion devices also made

integrated electric drive possible because these devices can efficiently convert large

amounts of electrical power into differing forms needed for propulsion and nonpropulsion uses. Electric-drive systems using AC motors21 control the speed of the

motor by varying the frequency of the electric power fed from the motor drive. This

made the electrical power unsuitable for other electrical systems on the ship, which

require electric power at a stable frequency. As a result, older AC electric drive

systems could be used only for ship propulsion and could not be integrated with other

systems aboard the ship to produce an integrated electric drive.

In 1985, the United Kingdom took advantage of these developments and began

building a new class of frigates, known as the Duke class or Type 23 ships, which

employ a combined diesel-electric and gas turbine-mechanical drive propulsion plant.

The ships use a lower-power diesel-electric drive system for quiet sonar-towing

operations at speeds of up to about 15 knots, and a gas turbine-mechanical drive

system for higher-speed operations up to the ships' maximum sustained speed of about

28 knots.22 The first Type 23 frigate entered service in 1990 and their drive systems

have been favorably received. The ships use much less fuel than comparably sized

mechanical-drive ships such as the U.S. Navy’s Oliver Hazard Perry (FFG-7) class

frigates, have demonstrated high reliability, and are very quiet compared to earlier

ships when operating at lower speeds.

In 1987, the cruise ship Queen Elizabeth II underwent an overhaul during which

its mechanical-drive system was replaced with an integrated electric-drive system.

20

Distortions in the electrical power that is delivered to the motor can lead to noiseproducing irregularities in the motor’s performance.

21

Some electric motors are designed to use AC current; others are designed to use DC

current. It was not practical to make conventional DC motors with ratings of more than about

10,000 or 15,000 horsepower. That was large enough to power small non-nuclear-powered

submarines (where DC motors are widely used), but not enough to power large surface ships

at higher speeds. Electric-drive-equipped surface ships thus tended to use AC motors.

22

For a discussion, see Preston, Christopher. Novel Electric Drive For the RN’s Type

23 ASW Frigates. Jane’s Defence Weekly, September 7, 1985: 473, 475, 477.

CRS-25

This system was also deemed successful in operation and set the stage for widespread

adoption of electric-drive technology in the cruise ship industry. Today, most if not

all cruise ships under construction in the world are being built with electric drive.

Electric drive is now used almost exclusively in icebreakers and floating offshore oil

platforms, and is becoming more common in passenger and car ferries. Other kinds

of commercial ships now being built with electric drive include shuttle tankers, pipeand cable-laying ships, and research ships.

Current Status of Electric Drive

Outside the United States. Several foreign countries, particularly in Europe,

have developed, are developing, or are using electric-drive technology in commercial

ships, naval ships, or both. Much of the development work is government-financed.

These countries include the United Kingdom, France, Germany, Italy, the

Netherlands, Finland, Sweden, Canada, Russia, Japan, South Korea, and China,

among others.

Commercial Ships. The electric-drive systems used today in cruise ships and

other commercial ships are generally made overseas, primarily in Europe. The three

primary European-based electric-drive suppliers are Alstom (previously known as

Cegelec)23 and Asea Brown Bovieri (ABB)24 – which together account for most of

the electric-drive systems in operation today – and Germany-based Siemens, which

has a smaller market share but is considered a leader in permanent magnet motors and

associated advanced motor drives.

Naval Ships. Developments regarding electric-drive technology in foreign

(mostly European) navies include the following:

In General. Virtually all of the world’s non-nuclear-powered submarines have

electric-drive systems. Until recently, all of these submarines were diesel-electric

boats that use diesel engines as the prime movers. A few countries, particularly in

Europe, are now introducing so-called air-independent propulsion (AIP) systems that

use fuel cells, Sterling engines, or closed-cycle diesel engines rather than conventional

diesel engines as the prime movers. In spite of the change in the prime mover,

however, these submarines are still electric-drive boats.25

23

As discussed later, Alstom is an international company headquartered in Paris that has

marine operations in Britain, France, Germany, and the United States (in Pittsburgh and

Philadelphia). The firm’s marine business is directed from Britain.

24

25

ABB’s primary electric-drive facilities are in Finland and Italy.

For examples of discussions of AIP systems on non-nuclear-powered submarines, see

Walsh, Don. The AIP Alternative. Sea Power, December 1999: 34-37; Scott, Richard.

Boosting the Staying Power of the Non-Nuclear Submarine. Jane’s International Defense

Review, No. 11, 1999: 41-44, 46, 48-50; Ritterhoff, Jurgen. Class 214 – A New Class of AirIndependent Submarines. Naval Forces, No. 5, 1998: 94-98, 100; Windolph, Wolfgang. The

Better AIP. Naval Forces, No. 4, 1998: 114-116, 118-120; Scott, Richard. Power Surge.

Jane’s Defence Weekly, July 1, 1998: 24-27; de Lionis, Andres. The Allure of AIP Beckons

the Navies of Developing States. Jane’s Intelligence Review, February 1998: 39-41;

(continued...)

CRS-26

NATO. Electric-drive technology was endorsed as feasible and viable for future

frigate-sized surface combatants by an October 1998 report from a NATO technical

study group on future naval ship design.26 This study was undertaken by 50 technical

experts from more than 30 companies in 8 NATO countries (Canada, France,

Germany, Italy, the Netherlands, Spain, Turkey, and the United Kingdom).

United Kingdom. In addition to the Type 23 frigates discussed above, whose

electric-drive system was provided by Alstom (then Cegelec), the British Navy has

two auxiliaries that use electric drive – a seabed operations vessel and a former

commercial support ship that was converted into a forward repair ship. The United

Kingdom is also using commercial (modified cruise ship) electric-drive systems in two

new Albion-class amphibious ships and two new Wave-class auxiliary oilers, all now

under construction, and on two planned logistics landing ships.

The British Navy has approved and recently re-endorsed a 1996 Marine

Engineering Development Strategy that envisages using electric drive on future

warships and auxiliaries. The British Navy is now seriously considering using electric

drive on a variety of planned warship classes, including a medium-sized (by U.S.

standards) aircraft carrier, a nuclear-powered attack submarine, and two surface

combatants – the Type 45 destroyer and the Future Surface Combatant (FSC). The

baseline design for the FSC includes electric drive. Given the now-established use of

commercial electric-drive systems on recently ordered British amphibious and

auxiliary ships, it appears likely that future classes of such ships in the British Navy

will also use electric drive.

The British Ministry of Defence has funded development of advanced electricdrive technologies for possible use on future ships under an Integrated Full Electric

Propulsion (IFEP) program established in 1996. These technologies include a

transverse-flux permanent magnet motor being developed by Alstom and Rolls Royce.

The British Navy plans to build a land-based IFEP technology demonstrator,27 and is

using electric drive on an experimental trimaran (three-hulled) research ship (the

Triton) that is intended to explore hull and mechanical options for future warships.

25

(...continued)

Robertson, Thomas. Air Independent Propulsion. Naval Forces, No. 6, 1996: 36-39; Annati,

Massimo. AIP Systems: a Solution for Everybody? Military Technology, No. 11, 1996: 107108, 110-112; Donaldson, A. J. Submarine Power Sources For the Mission. Naval

Engineers Journal, May 1996: 129-146 (includes comments by others).

26

North Atlantic Treaty Organization. NATO All Electric Ship, NIAG SG/54 PreFeasibility Study, Final Report. NATO, Brussels, 1998. (Document AC/141-D/737, NIAG

[NATO Industrial Advisory Group] - D(98) 9. For a published summary of this study, see

Weigel, Dieter. NATO Study on An All Electric Warship. Naval Forces, No. 5, 1999: 4549. The results of the NATO study are also briefly summarized in Pengelley, Rupert.

Turning The Naval Propulsion Helm. Jane’s Navy International, January/February 1999:

10-15.

27

For a discussion, see Scott, Richard. Rivals [sic] Teams Power Up For Electric Ship

Demonstrator. Jane’s Defense Weekly, December 22, 1999: 12.

CRS-27

(As discussed below, the U.S. Navy is also participating in the Triton experimentation

program.)28

France. France’s nuclear-powered submarines all use electric-drive technology.

One press report states that “the French Navy is understood to have decided in

principle to adopt integrated full electric propulsion for its future warships.”29

Jeumont Industrie in France is supplying an axial-gap permanent magnet motor for the

new Scorpene-class non-nuclear-powered submarine being built in France for Chile

and is currently developing a permanent magnet motor for use in the next French

nuclear-powered submarine. According to one source, Jeumont is developing a type

of electric motor not otherwise discussed in this report – a superconducting

permanent magnet motor.30

Germany. Germany is using electric-drive systems in minesweepers, an

oceanographic ship (whose system incorporates a permanent magnet motor), and nonnuclear-powered submarines. The new Type 212 German non-nuclear-powered

attack submarine, scheduled to enter service in 2003, will use an advanced submarine

electric-drive system that includes fuel cells as an alternative to a diesel engine and a

permanent magnet motor, both made by Siemens. A second German company,

Magnet-Motor, is also involved in developing permanent magnet motors for use in

all military services. Work on permanent magnet motors by both firms began in the

1980s. The German firm MTG (Marine Technische Gesellschaft) Marinetechnik

reportedly has completed a design study for the German Ministry of Defense for a

3,000-ton SWATH (small waterplane area, twin-hull) electric-drive demonstration

ship featuring a radial-gap permanent magnet motor; the ship is being built by the

German shipbuilder Thyssen Nordseewerke and is expected to be completed in

2002.31

Italy. Italy is building its own German-designed Type 212 submarines; these

ships will also use Siemens-made fuel cells and permanent magnet motors. ABB in

Italy developed a prototype permanent magnet motor for the Italian submarine

program, but the Italian Navy selected the Siemens motor.

Netherlands. A significant recent example reflecting state-of-the-art electricdrive technology in deployed form in a warship is the Dutch Navy’s new amphibious

ship Rotterdam, which entered service in 1998. This 12,750-ton ship has an electric-

28

For more on the British Navy’s electric-drive development efforts, see Pengelley,

Rupert. Future Electric, Harnessing the Promise of IFEP. Jane’s Navy International,

July/August 1997: 14-15, 17-18, 20-21; Hodge, CG, and D.J. Mattick. The Electric Ship,

an Update. Review of Naval Engineering, Vol. 51, No. 4: 11-18; and Pengelley, Rupert.

Turning The Naval Propulsion Helm. Jane’s Navy International, January/February 1999:

10-15. Electric-drive technology is also used on British-owned cruise ships.

29

Pengelley, Rupert. Europeans Go For Electric Drive. Jane’s Navy International,

January/February 1999: 3.

30

31

Electric drive is also being used in French cruise ships and chemical tankers.

Pengelley, Rupert. Europeans Go For Electric Drive. Jane’s Navy International,

January/February 1999: 3.

CRS-28

drive system provided by the firm Holec Ridderkerk featuring induction motors. The

ship has a maximum sustained speed of 19 knots.32 In addition, “in January 1998 the

Netherlands released its All Electric Ship (AES) strategy document, large parts of

which are characterised as having been taken verbatim from the UK antecedent.”33

Russia. Russia uses electric-drive technology in icebreakers. Given Russia’s

history as a significant naval power and as a developer of various naval technologies

(including both nuclear and gas-turbine propulsion), it is very possible that Russia may

be attempting to develop (within available resources) more advanced electric-drive

technologies.

In the United States. Electric-drive technology is used on a few U.S.

government ships and is being developed in the United States by both the U.S. Navy

and private industry.34

U.S. Government Ships. U.S. government ships equipped with electric drive

include the new U.S. Coast Guard icebreaker Healy, which was procured in FY1990FY1993 and entered service in 1999, three older icebreakers, several Military Sealift

Command (MSC)-operated TAGOS-type ocean surveillance ships procured between

FY1979 and FY 1990, a few TAGS-type ocean surveying ships that were procured

in FY1990-FY1996, and a few AGOR-type oceanographic research ships that are

operated by academic institutions under the Navy’s University National

Oceanographic Laboratory System (UNOLS).

U.S. Navy Study and Development Efforts. The Navy’s more recent electricdrive technology study and development efforts began in 1979 with an assessment of

then-current technology in the area. Electric drive was selected by the Navy for use

in the DDGX, which became the Arleigh Burke (DDG-51) class destroyer. This

decision, however, was subsequently reversed due to concerns over cost and schedule

risk.

In 1984, the Navy explored designs for a potential new frigate (FFX) intended

to replace the Navy’s aging Knox (FF-1052) class frigates. The FFX program was

subsequently cancelled but informed later Navy efforts on electric drive.

A series of Navy studies in 1986-1989 on a potential destroyer-like ship called

the Battle Force Combatant included consideration of a variety of new propulsion

technologies, including electric drive. This work was carried forward under the

Integrated Warship Systems Demonstration Program (IWSDP), which was later

dropped.

32

Electric-drive systems are also used in Dutch ferries.

33

Pengelley, Rupert. Turning the Naval Propulsion Helm. Jane’s Navy International,

January/February 1999: 10-15.

34

For an overview of U.S. government and industry efforts on electric drive, see Walsh,

Edward J. Transforming Shipboard Power. Sea Power, October 1999: 50-52.

CRS-29

In September 1988, then-U.S. Chief of Naval Operations Admiral Carlisle Trost

endorsed the use of electric drive for the Navy's next surface combatant class.35 In

1989-1993, the Navy funded full-scale advanced development work on an electricdrive system for a SWATH ship. In 1989, the Navy began development work on a

zonal electrical distribution system (ZEDS), which would form part of an integrated

electric-drive system. An AC version of such a system has been incorporated into

later (Flight IIA) ships in the DDG-51 program. The first Flight IIA DDG-51 was

procured in FY1994 and is scheduled to enter service in 2000. A DC version of

ZEDS is under development.

U.S. Navy IPS Program. In 1992, a Navy program on a 21st Century Destroyer,

using work done under the Navy’s Advanced Surface Machinery Program (ASMP),

concluded that incorporating an electric-drive system into the ship’s design could

actually reduce its procurement cost. To engineer this system and carry out riskreduction work, the Navy in 1995 established its Integrated Power System (IPS)

program.36

35

For information on this Navy interest in electric drive during this time, see, for

example, Russell, James A. Navy Eyes Electric Drive For New Ships. Navy News &

Undersea Technology, January 3, 1986: 1-2; Russell, James A. Electric-drive Ship Gets

Boost From Superconductors. Navy News & Undersea Technology, July 3, 1987: 4; Elliott,

Frank. Electric Drive Warships Will Revolutionize Ship Design. Navy News & Undersea

Technology, June 6, 1998: 4-5 (see also related article on pages 1 and 3); Rumsey, Anne.

Navy Ready To Award Work For Electric Drive. Defense Week, July 25, 1988; Black,

Norman. Electricity Proposed As Power Of The Future For Navy Warships. Hartford

Courant, September 30, 1988: 8; Trost Endorses Electric Drive, Promises Use In Future

Ships. Navy News & Undersea Technology, October 3, 1988: 1, 3; Halloran, Richard. U.S.

Plans Electric Power to Drive New Warships. New York Times, October 9, 1988: 37;

Matthews, William. After 75 Years, Navy Returns to Electricity to Power Its Ships. Defense

News, October 10, 1988: 6; Rumsey, Anne. Adm. Trost Puts Electric Drive Into High Gear.

Defense Week, November 28, 1988: 5; Friedman, Norman. Electric Drive Revisited. U.S.

Naval Institute Proceedings, December 1988: 149; Navy Begins Work on Propulsion System

of the Future. Navy News & Undersea Technology, February 13, 1989: 4-5; Walsh, Edward

J. Prime Movers. Sea Power, March 1989: 55-58; Rumsey, Anne. Navy Slows Drive For

Electric-Powered Ships. Defense Week, May 15, 1989: 7; Lane, Maury. Navy Designs

Radical Ship Propulsion System. Defense News, July 3, 1989: 1, 28; Superconductor

Technology Would Cost 25% Less Than Navy Electric Drive Plan. Inside the Navy, August

28, 1989: 7; Electric Transmission and Podded Propulsors For the US Navy of the 2000s.

Maritime Defence, November 1989: 355-356; Navy `Integrated Electric Drive' R&D

Accelerates. Sea Power, February 1990: 42-43; Navy Abandons Goal To Install Integrated

Electric Drive on DDG-51 Destroyer. Inside the Pentagon, November 15, 1990: 3-4; Navy

Officials Say Service Is Abandoning Electric Drive on DDG-512 Ship. Inside the Navy,

November 19, 1990: 1, 11-12; Lawson, Richard. Advanced Ship-Propulsion Program

Changes Name, Focuses on Affordability. Inside the Navy, November 18, 1991: 16;

Rosenberg, Eric. It’s Wait And See For Navy’s Electric Drive. Defense Week, January 21,

1992: 2.

36

For descriptions of the IPS program in its earlier stages, see IPS: The US Navy’s

Next-Generation Power/Propulsion System. Maritime Defence, December 1996: 278-279;

Doerry, Norbert, et al. Powering the Future with the Integrated Power System. Naval

Engineers Journal, May 1996: 267-282; Walsh, Edward J. Surface Fleet Looks To “All(continued...)

CRS-30

In 1995, the IPS program supported advanced development work on a partialscale axial-gap permanent magnet motor. This work was done by Newport News

Shipbuilding, Kaman Electromagnetics Corporation (KEC) and the Naval Surface

Warfare Center (NSWC) at Annapolis.

Since 1995, the IPS program has carried out full-scale advanced development

work on electric drive. The IPS program recently completed construction of a fullscale, land-based demonstration electric-drive system. Testing of this system, located

at the Naval Sea Systems Command (NAVSEA) Advanced Propulsion and Power

Generation Test Site (APPGTS) in Philadelphia (on the site of the former Philadelphia

naval shipyard), began in May 1999 and is scheduled to continue through FY2001.

The Navy is using this land-based system as part of a demonstration and riskreduction effort for electric-drive technology in general and the DD-21 program in

particular. A second goal is to develop the site as a test facility for future electricdrive technology developments. The Navy’s prime contractor for this system is

Lockheed Martin, but much of the actual equipment was provided by Alstom.

Several other firms are also involved.

The IPS program is also testing electric-drive technology with the British Navy

on the British technology demonstration ship Triton as part of a joint U.S.-U.K.

technology demonstration effort. Specifically, the U.S. Navy will use the Triton to

test elements of the IPS program’s ship-wide power distribution system. At-sea tests

with the Triton are scheduled to begin in 2001 and continue to 2003.37

In 1998, the IPS program was transferred to the DD-21 program office.

Although most of the Navy’s work on electric drive in recent years has been carried

out under the IPS program, additional work has been conducted outside the IPS

program. For example, development work outside of the IPS program on electric

drive for submarines was funded in FY1998. This work focused on developing

submarine-suitable electric-drive systems that employ permanent magnet motors.

Participants in this work include General Dynamics’ Electric Boat and ElectroDynamics divisions, Newport News Shipbuilding, KEC, Eaton, and Westinghouse

Electro-Mechanical Division.

U.S. Navy Funding for Electric Drive. The tables below show prior-year

(FY1989-FY2000) and programmed (FY2001-FY2005) Navy funding for electric

drive.38

36

(...continued)

Electric Ships.” Sea Power, May 1996: 33-34.

37

U.S. Department of the Navy. TRIMARAN Integrated Power System (IPS) Project

Plan. Washington (?), 1998, 16 p. (December 1998)

38

These tables do not include funding for research and development electric-drive

technologies carried by the Office of Naval Research (ONR). Prior to FY1994, ONR funding

for electric drive amounted to less than $1 million per year. For FY1994 through FY2000,

ONR funding for electric drive was as follows: $4.3 million (FY1994), $2.1 million

(FY1995), $13.1 million (FY1996), $21.8 million (FY1997), $21.5 million (FY1998), $26.8

(continued...)

CRS-31

Table 2. Prior-Year Funding for Navy Electric Drive Research and

Development (FY1989-FY2000)

(millions of current dollars)

FY89

FY90

FY91

FY92

FY93

FY94

FY95

FY96

FY97

FY98

FY99

FY00

24.0

29.0

52.0

12.4

9.1

9.7

13.7

28.7

21.3

26.5

31.8

25.7

Table 3. Programed Funding for Navy Electric Drive Research and

Development (FY2000-FY2005)

(millions of current dollars)

FY00

FY01

FY02

FY03

FY04

FY05

25.7

84.1

106.3

69.3

26.9

10.0

Industry Development Efforts. Several private-sector firms in the United States

are now pursuing electric-drive technology for the U.S. Navy market. At least three

private-sector entities are offering complete electric-drive systems to the Navy:39

! Alstom (previously known as Cegelec), an international company

headquartered in Paris that has marine operations in Britain, France, Germany,

and the United States (in Pittsburgh and Philadelphia). The firm’s marine

business is directed from Britain. Alstom has been involved in marine electricdrive technology since 1920 and today is a leading international supplier of

commercial and naval electric-drive systems. The company supplies electricdrive systems featuring synchronous motors and is also developing systems

featuring induction and permanent magnet motors.40

38

(...continued)

million (FY1999), and $47.9 million (FY2000). Source: Department of Defense information

paper on ONR initiatives supporting electric drive, provided to CRS by the Navy Office of

Legislative Affairs, July 17, 2000 (LA-581-379).

39

For discussions of industry efforts on electric drive, see Nagy, Barbara. Propelled By

Urgency. Hartford Courant, April 14, 2000: E1; Lerman, David. Power Play. Newport

News Daily Press, March 12, 2000: 1; Walsh, Edward J. A Fundamental Change of

Direction. Sea Power, March 2000: 24-25; Schweizer, Roman. Newport News-Kaman

Unveil Electric Drive System to Challenge GD Team. Inside the Navy, August 16, 1999: 5-6;

Muradian, Vago. NNS-Kaman Unveil Modular Electric Propulsion for DD-21. Defense

Daily, August 13, 1999: 6-8; Holzer, Robert. Newport News Pushes Electric Drive Funding

Scheme. Defense News, May 31, 1999: 6; Holzer, Robert. General Dynamics Pushes for

Electric Drive. Defense News, April 19, 1999: 4, 26.

40

Alstom has supplied electric-drive components or systems for scores of commercial

ships and several naval ships, including the British Navy’s Type 23 frigates, which entered

service starting in 1990, its two new Albion-class amphibious ships, which are scheduled to

enter service in 2002-2003, and its two new Wave-class auxiliary oilers, which are scheduled

to enter service in 2000-2001. In addition to being a principal supplier of the U.S. Navy’s

(continued...)

CRS-32

! an industry team led by General Dynamics Corporation, a leading designer

and builder of U.S. Navy ships.41 The team includes, among other firms, GD’s

Electric Boat and Bath Iron Works shipyards, two other GD divisions,

Westinghouse Electro-Mechanical Division (WEMD), Eaton Controls, and

Northrop Grumman Marine Systems. This team is developing an electric-drive

system featuring a permanent magnet motor.

! an industry team led by Newport News Shipbuilding (NNS), another leading

designer and builder of U.S. Navy ships.42 The NNS-led team also includes,

among other firms, Kaman Electromagnetics Corporation (KEC), which

develops and builds electric motors and related systems. This team is also

developing an electric-drive system featuring a permanent magnet motor.43

In addition to these three entities, other U.S. firms are also involved in

developing electric-drive technologies or components. These include, among others:

! American Superconductor of Westborough, MA, which is developing, in

conjunction with Rockwell Corporation, a superconducting synchronous

motor (and also superconducting wire and related technologies that could be

incorporated into various electrical systems), and

! General Atomics of San Diego, CA, which is developing a superconducting

homopolar motor that was previously under development for many years by

the U.S. Navy.

Associated U.S. Navy Ship Programs

40

(...continued)

land-based electric-drive prototype system in Philadelphia, Alstom supplied the electric-drive

systems for the U.S. Coast Guard’s new icebreaker, the Healy, and the Navy’s new ocean

surveillance ship Impeccable (TAGOS-23), which was procured in FY1990 and entered

service in 1999. For a discussion of Alstom’s efforts in Philadelphia, see Holcomb, Henry

J. Powering Up For Tomorrow’s Ships. Philadelphia Inquirer, June 5, 2000.

41

General Dynamics owns 3 of the 6 shipyards that build major ships for the Navy – the

Electric Boat Corporation of Groton, CT and Quonset Point, RI, which builds nuclearpowered submarines, Bath Iron Works Corporation of Bath, ME, which builds surface

combatants and amphibious ships, and National Steel and Shipbuilding Company (NASSCO)

of San Diego, CA, which builds auxiliary and sealift ships.

42

NNS, which is located in Newport News, VA, builds nuclear-powered aircraft carriers

and nuclear-powered submarines for the Navy.

43

Although the General Dynamics- and NNS-led teams are both developing electricdrive systems featuring permanent magnet motors, there are numerous differences in these two

systems. For example, although both teams employ permanent magnet motors, the two teams

have taken different approaches to the design of the control mechanisms for the motors, which

is why the NNS-led team sometimes refers to its motor as a brushless DC motor.

CRS-33

Several U.S. Navy ship-acquisition programs are (or could be) associated with

the Navy’s electric drive program, including the following:

! DD-21 Land-Attack Destroyer Program. This is the Navy’s program to

develop and procure a next-generation surface combatant following the

completion of the current Arleigh Burke (DDG-51) Aegis destroyer

procurement program. The first DD-21 is to be procured in FY2005; a total

procurement of about 32 ships is envisioned. As mentioned earlier, the Navy

announced in January 2000 that the DD-21 will use electric drive. In light of

this announcement, as well as the size of the DD-21 program and the fact that

the DD-21 design is to form the basis of the Navy’s next-generation CG-21

cruiser (which is to be procured following completion of the DD-21 program,

perhaps sometime after FY2015), the DD-21 program is widely viewed as the

ship-acquisition program currently most closely and significantly associated

with the Navy’s electric-drive effort.44

! Virginia (Ssn-774) Class Attack Submarine Program. The first ship in this

program, previously known as the New Attack Submarine (NSSN) program,

was procured in FY1998. The second ship was procured in FY1999, and

current plans call for the next five ships to be procured at a rate of one per year

during the period FY2001-FY2005. A total of perhaps 30 ships might

eventually be procured. The current Virginia-class design uses a mechanicaldrive system, but there has been much discussion of building future units in the

class to a modified design that uses electric drive. Because of the potential size

of the program, and potential for the Virginia-class design to form the basis of

the Navy’s next-generation ballistic missile submarine (which might begin

procurement around 2020), the Virginia class program is also significantly

associated with the Navy’s electric-drive effort.45

! TADC(X) Auxiliary Dry Cargo Ship Program. This 12-ship program is

intended to provide replacements for several older Navy auxiliary ships. The

first TADC(X) was procured in FY2000. The second ship is to be procured

in FY2001, and the remaining 10 ships in the program are to be procured

during the period FY2002-FY2005.

! JCC(X) Joint Command and Control Ships. This program would replace

the Navy’s four aging command ships with a new class of four Joint Command

and Control (JCC[X]) ships. Under the Navy’s current plan, the first JCC(X)

is to be procured in FY2004.

! LHA Replacement Ship Program. This program would replace the Navy’s

5 aging Tarawa (LHA-1) class amphibious assault ships, which will reach the

end of their 35-year service lives during the period 2011-2015. The first of

44

For more on the DD-21 program, see CRS Report 97-700 F, Navy DD-21 Land

Attack Destroyer Program: Background Information and Issues for Congress, by Ronald

O’Rourke.

45

For more on the Virginia-class program, see CRS Report RL30045, Navy Attack

Submarine Programs: Background and Issues for Congress, by Ronald O’Rourke.

CRS-34

these ships, LHA-1, is to be replaced by LHD-8, which will be the eighth Wasp

(LHD-1) class amphibious assault ship. LHD-8 is currently planned for

procurement in FY2005, but its procurement could be accelerated to an earlier

year. Ships to replace LHAs -2, -3, -4, and -5 will be procured after LHD-8.46

! CVN(X) Program. The CVN(X) is the Navy’s planned next-generation

aircraft carrier. Under current Navy plans, the first ship in the program

(CVN[X]-1) is to be procured in FY2006 and the second (CVN[X]-2) in

FY2011.47

! Coast Guard Deepwater Project Cutter. The Deepwater project is an

ambitious Coast Guard program to replace its aging deepwater (i.e., far-fromshore)-capable cutters and aircraft. Under the Coast Guard’s schedule for the

Deepwater project, the first new cutter would be procured in FY2002.48

Navy Report to Congress

The following is the executive summary of the Navy’s March 1999 report to

Congress on prospects for a common electric drive system for Navy ships, as

reprinted on pages 9 and 10 of the April 12, 1999 issue of Inside the Navy:49

The Navy evaluated electric drive alternatives for future submarines, surface

combatants, and aircraft carriers. A team of Naval Sea Systems Command

technical experts studied the feasibility of common electric components for

integrated power (electric drive) systems on DD-21, CVN (X), and a VIRGINIA

Class (NSSN) variant, and concluded the following:

–

a common motor, or multiples of a common motor, could

accommodate the range of main engine horsepower and shaft

speeds for surface combatants, aircraft carriers, and submarines;

–

generator commonality is limited to surface combatants and

submarines due to size and power requirement incompatibility

between these platforms and aircraft carriers; and

–

a common motor controller for all applications is not practicable,

however common subcomponents for all three applications is

feasible.

46

For more on LHD-8, see CRS Report RS20563, Navy LHD-8 Amphibious Assault

Ship: Background and Issues For Congress, by Ronald O’Rourke.

47

For more on the CVN(X) program, see CRS Report 98-359 F, CVN-77 and CVX

Aircraft Carrier Programs: Background and Issues for Congress, by Ronald O’Rourke.

48

For more on the Deepwater project, see CRS Report 98-830 F, Coast Guard

Integrated Deepwater System: Background and Issues for Congress, by Ronald O’Rourke.

49

For news coverage of Navy report, see Schweizer, Roman. Navy Wrestles With

Prospects, Price of Electric Drive for Subs, Ships. Inside the Navy, April 12, 1999: 8-9;

Holzer, Robert. U.S. Navy Strives To Electrify Future Combat Fleet. Defense News, April

5, 1999: 1, 50.

CRS-35

For future aircraft carriers, there will be a need for an increased electric

generation capacity for loads such as an electric catapult and recovery system,

future electrically powered weapons, and countermeasures. With this in mind, the

Naval Sea Systems Command has studied options for electric drive and increased

electric generation capacity. These studies concluded that while electric drive was

feasible, mechanical drive is more appropriate at this time. For a ship the size of

an aircraft carrier, electric drive did not offer space or weight savings over a steam

driven mechanical drive design with appropriately sized turbine generators. In

addition, the studies found that the most affordable method to achieve the objective

of increased electric generating capacity was to use mechanical drive with larger

turbine generators.

A Navy integrated power systems development program, which demonstrates

a full size induction motor and other components for potential use in future surface

ships, is entering the full-scale system test phase. This motor would not be

appropriate for submarine use because it does not have the power density or

acoustic performance needed for submarine applications.

The Navy has done extensive work to assess the viability of superconducting

direct current (DC) homopolar motors for electric drive. However, there are

significant technical challenges associated with homopolar motors. While come

progress has been made in overcoming these challenges, more work is required. As

a result, superconducting homopolar motors are not considered a viable option for

electric drive at this time.

The Navy has concluded that the radial-gap permanent magnet motor

possesses the power density, acoustic performance, and maturity of technology to

be a viable propulsion motor common to the broadest range of ships. We believe

that this is now possible due to the recent advancements in technology which are

being pursued by industry in developing propulsion motors based on permanent

magnet motor technology.

The Navy recognizes that a common development program would benefit

both future surface combatants and submarines. Such a corporate program would

allow the Navy to maximize life cycle cost reductions while satisfying performance

needs of the broadest range of platforms. Common technology presents an

opportunity for a common support structure such as personnel, training and

maintenance facilities.

A Navy corporate integrated power system development program will benefit

future ships, and allow horizontal integration of technology, components and

training across the broadest range of ships. Therefore, the Navy is currently

considering an expansion of its integrated power systems development to a

corporate Navy program including state-of-the-art permanent magnet motor

technology. Our plan includes an aggressive evaluation of the application of these

technologies and the benefits associated for each type of platform including life

cycle cost, logistics, and training reductions.

A summary comparison of mechanical drive versus an integrated power system

(electric drive) is provided in Table I.

CRS-36

Table I - Mechanical vs. Integrated Power System Comparison

Submarine

Mechanical

Drive

Integrated

Power System

with Induction

Motor

Integrated

Power System

with Permanent

Magnet Motor

Integrated

Power System

with Homopolar Motor

– Does Not

Meet Future

Acoustic Needs

– Does Not

Meet Future

Acoustic Goals

+ Meets Future

Acoustic Goals

– Significant

Technology

Development

Required

– Required

Induction Motor

Size Is Too

large

Surface

ship

– No Fuel

Economy

Improvement

+ Provides

Flexible Power

Distribution

– No Flexible

Power

Distribution

+ Provides

Naval

Architectural

Flexibility

+ Life Cycle

Cost Savings

+ Lower

Development

Risk than

Permanent

Magnet Motor

+ Meets Motor

Size

Requirements

+ Commonality

Is possible

+ Commonality

Is possible

+ Provides

Flexible Power

Distribution

– Significant

Technology

Development

Required

+ Provides

Naval

Architectural

Flexibility

+ Life Cycle

Cost Savings

– Commonality

Not Possible

– Motor Larger

than Permanent

Magnet Motor

Aircraft

Carrier

+ Future Power

Generation

Needs Can Be

Met With New

Electric Plant

+ Most

Affordable

Carrier

Alternative

+ Potential to

meet future

goals

+ Potential to

meet future

goals

– Not Cost

effective for

CVN (X)

– Not Cost

effective for

CVN (X

– Significant

Technology

Development

Required

CRS-37

Note that the table does not specifically address electric-drive systems featuring

a regular (non-superconducting) synchronous motor (like those in the commercial

electric-drive systems currently operating on cruise ships and other ships) or a

superconducting synchronous motor.

Congressional Reaction to Navy Report

In marking up the Administration’s proposed FY2000 defense budget, the House

Armed Services Committee stated the following in reaction to the Navy’s March 1999

report:

The committee notes the Navy’s increased interest in the development of

electric drive propulsion technology and the potential use of electric drive

propulsion in future surface combatants and submarines, including insertion of an

electric drive propulsion system in the DD-21 land attack destroyer and in the New

Attack Submarine (NSSN) programs. A common integrated electric drive system

appears to offer significant advantages, however, implementation of such a system

has been limited by the technology needed for reliable electric motors of the power

(approximately 30,000 to 50,000 shaft horsepower (shp)) required. The

committee is aware that several alternative electric propulsion motor concepts have

been proposed that are of varying degrees of technical maturity.

The statement of managers accompanying the conference report on H.R.

4103 (H.Rept. 105-746) directed the Secretary of the Navy to provide a report to

the Congress which evaluates the installation of a common integrated electric drive

system for DD-21, a NSSN variant, and [also evaluates designs for] the nextgeneration CV(X) aircraft carrier with both a common integrated electric drive

system and a conventional mechanical drive system. The Secretary’s report, dated

March 1, 1999, states that the Navy has concluded that the radial-gap PM

[permanent magnet] motor possesses the power density, acoustic performance, and

maturity of technology to be a viable propulsion motor common to the broadest

ranges of ships and that the Navy is currently considering expanding its IPS

[Integrated Power Systems] development [program] to a corporate Navy program

that will include state-of-the-art permanent magnet motor technology....

The committee will consider recommendations by the Secretary for further

development and demonstration of electric drive propulsion technology for Navy

ships which identify necessary funding and provide a program plan for

development.50

The Senate Armed Services Committee, in its markup, stated that the Navy’s

integrated power systems development effort

is designed to explore technologies required to develop power systems that could

provide innovative means of generating, controlling, distributing, and using

electricity in future ships. Propulsion motor development is a central focus of

these explorations by the Navy and, independently, by commercial entities.

50

H.Rept. 106-162 of May 24, 1999 (House Armed Services Committee Report on H.R.

1401, the FY2000 defense authorization bill), p. 194-195.

CRS-38

A recent Navy report entitled A Report to Congress on Navy Common

Integrated Electric Drive Systems, addressed electric drive alternatives for future

submarines, surface combatants, and aircraft carriers. The study reached several

conclusions, to include: (1) the radial-gap permanent magnet motor has the power

density, acoustic performance, and maturity of technology to be a viable

propulsion motor common to the broadest range of ships; and (2) superconducting

homopolar motors are not considered a viable solution for electric drive at this

time. The committee believes that broad application is an important aspect of

reducing life cycle costs to make the fleet of the future more affordable.

The committee understands that the Navy is considering an expansion of the

integrated power system program to include permanent magnet motor technology.

The committee encourages the Navy to take this step, however, the committee also

expects the Navy to continue the technology base investment in superconducting

alternatives as well, despite the fact that these technologies will not be mature

enough for immediate applications such as DD-21.51

Issues for Congress

Electric-drive presents several potential issues for Congress that can be divided

into two groups: those relating to electric-drive technology in general, and those

relating to the potential application of electric drive to specific ship-acquisition

programs. Each of these is discussed below.

Electric Drive in General

Electric Drive as a Technology Area. Although electric drive is often

discussed as a specific system that could be available in the near future for the DD-21

program, many elements of electric-drive technology have the potential to evolve and

improve over time. This suggests that policymakers might consider addressing

electric drive as not simply a proposal for a specific system that might require a few

nearer-term acquisition decisions, but as a broader technology area that might require

longer-term management and oversight and a series of research, development, and

procurement decisions stretching over the course of several years.

Given the many (and in some cases competing) possibilities for evolving and

improving electric-drive technology over time, conducting longer-term management

and oversight of electric drive as a technology area might be assisted by developing

an electric-drive technology development roadmap or master plan extending perhaps

10 to 25 years into the future. Such a roadmap, updated periodically, could help

place nearer-term investment decisions regarding electric-drive technology in the

context of potential longer-term opportunities, risks, benefits, and implications. In

recent years Congress has called for (and DoD has provided) master plans or

roadmaps in other naval technology-development areas, such as mine warfare and

anti-submarine warfare, that present multiple development opportunities stretching

out over a period of several years.

51

S.Rept. 106-50 of May 17, 1999 (Senate Armed Services Committee Report on S.

1059, the FY2000 defense authorization bill), p. 232-233.

CRS-39

Near-Term Costs. As noted in the background section, pursuing electric-drive

will incur higher near-term costs than a strategy that places continued emphasis on

mechanical-drive technology.

With regard to development costs, mechanical-drive propulsion for naval ships

is a very mature technology and would not necessarily require substantial amounts of

additional research and development funding for future naval ships.52 Developing

electric-drive technology for warships, in contrast, would require hundreds of millions

of dollars in research and development funding in coming years, particularly if the

technology is developed for submarines as well as surface ships, and if development

of more advanced electric-drive technologies is pursued.

With regard to production costs, several (but not all) sources for this report

stated that electric-drive systems initially would be more expensive to procure than

mechanical-drive systems.53 Although there are no precise figures, information

provided by some sources suggest the procurement cost of a non-commercial (Navydeveloped) electric-drive system might add a few tens of millions of dollars to the

total procurement cost of a Navy combat ship. An additional cost of, for example,

$15 million to $50 million would equate to an increase of about 2 percent to 6 percent

in the procurement cost of a surface combatant costing about $800 million (the

approximate target cost in FY2001 dollars of a DD-21 class land-attack destroyer),

or about 1 percent to 3 percent in the procurement cost of an attack submarine

costing about $2 billion (the approximate current cost of a Virginia [SSN-774] class

submarine). The cost premium for a commercial electric-drive system (which, as

discussed below, might be suitable for use in a Navy auxiliary ship) could be less than

that of a Navy-developed system that is engineered to be more power-dense, quiet,

and shock-resistant.

These sources, however, agreed that the procurement cost of electric-drive

systems would come down over time if more systems are procured and production

economies of scale for electric-drive technology increase, and as electric-drive

technology continues to improve. They also agreed that the higher initial costs of

electric-drive systems (both development and procurement) would be more than offset

over the longer run by reduced ship life-cycle operating and support costs.

Measuring and Assessing Cost Effectiveness. Several sources agreed that the

cost-effectiveness of electric drive should be examined not by focusing on the electricdrive system or any of its components in isolation, but rather by examining the effect

that electric drive has on overall ship cost and capability. Focusing on the electric

drive system or any of its components in isolation, they stated, could overlook certain

effects of electric drive on total ship cost and capability and encourage optimization

of the design at the system or subsystem level rather than the total-ship level.

52

An exception would be if a decision were made to attempt to achieve significant

further improvement in the quieting of mechanical drive technology. Such an effort could

require significant additional research and development funding.

53

Some sources disagreed, stating that electric-drive would be roughly as expensive to

procure as mechanical-drive technology, and perhaps (a couple of sources stated) somewhat

less expensive.

CRS-40

In view of the potential for electric-drive technology to be applied across

multiple ship types, and of the proposal for a common electric drive system (or

common family of components), it might also be said that the cost-effectiveness of

electric drive might best be measured not only in terms of its effect on the total costs

and capabilities of individual ship designs, but also in terms of its effect on total fleet

costs and capabilities. In this view, just as it would be inappropriate to optimize the

application of electric drive at the system or subsystem level, so too it might be

insufficient to assess the cost-effectiveness of electric drive at the level of individual

ship designs. Such an approach may obscure the advantages of certain strategies for

applying electric drive on a fleet-wide basis. In particular, it is possible that an

electric-drive system that results in a suboptimal design for a particular kind of ship

may nevertheless enable a more optimal application of electric drive across multiple

ship types.

Since some of the most important projected potential benefits of electric drive

technology, such as ship life-cycle fuel savings, would accrue over many years, any

newly developed estimates of the costs and benefits of electric-drive technology

should arguably include not just shorter-term issues such as initial research and

development and procurement costs, but also measures that examine longer-term (i.e.,

life-cycle or total ownership) costs and warfighting effects as well.

Although electric-drive technology offers numerous potential cost and

warfighting benefits for Navy ships, relatively few precise estimates are available on

the magnitude of these benefits. Many of the available estimates, moreover, are

single-point estimates that relate to the potential costs or benefits of a particular

electric-drive technology concept as applied to a particular kind of ship under a

specific set of assumptions regarding ship service life and typical ship operating

speeds.

The scarcity of estimates that are both precise and systematic (rather than rough

or single-point) is currently providing ample room for firms involved in developing

electric-drive technology to make well-intentioned but also self-interested and

sometimes-conflicting presentations to policymakers on the technology. If not

redressed, the scarcity of precise and systematic estimates will make it difficult for

policymakers to assess with any precision the potential cost-effectiveness of electricdrive technology in general and (probably more significant) the relative costeffectiveness of differing technical approaches to achieving electric drive,

incorporating it in the fleet, and improving it over time. As a result, policymakers

would have more difficulty making decisions concerning electric drive, particularly

decisions relating to longer-term development of the technology following an initial

application to the fleet. More precise and systematic estimates may be produced by

a study on electric drive that is being done for the Navy by the Rand Corporation and

the Center for Naval Analyses.54

The Navy’s interest in electric-drive technology is consistent with the decisions

of commercial ship operators (especially cruise ship operators) and other navies in

54

Castelli, Christopher J. Navy Plans To Study Potential of Electric Drive for Ships and

Subs. Inside the Navy, December 28, 1998:1, 10.

CRS-41

recent years to move to electric-drive technology for their own ships. The

commercial ship industry’s shift from mechanical- to electric-drive technology

suggests that electric drive offers demonstrated advantages, at least for large ships,

in areas such as reduced fuel costs, increased payload space (for cruise ship operators,

this can translate into additional passenger cabins or other revenue-generating spaces),

and perhaps reduced propulsion plant noise.

The strong interest in electric drive by other navies (particularly in Europe), and

the reasons they have identified for pursuing the technology, provide support for the

argument that electric drive offers a variety of warfighting and life-cycle cost

advantages for naval ships. The British Navy’s interest in electric drive is particularly

noteworthy not only because of the variety of ships that the United Kingdom is

considering to equip with electric drive, but also because the British Navy in the past

has adopted (or invented) important naval technologies that were later adopted by the

U.S. Navy.

The interest shown by other navies in electric drive, however, also demonstrates

that there are multiple technical approaches that can be pursued. For example, both

the 1998 NATO report and the British Navy’s development program highlight the

transverse-flux version of the permanent magnet motor as well as the radial gap (i.e.,

radial-flux) version, while permanent magnet motor efforts in the United States focus

more exclusively on the radial-gap version. There are also actual or potential

differences between the U.S. and European approaches to other components of

electric drive, such as the ship-wide electrical power distribution system. Thus, while

the interest shown by other navies in electric drive tends to support the U.S. Navy’s

interest in pursuing the technology, it also arguably underscores the need to carefully

evaluate the relative merits of different technical approaches.

Technical Risk. As noted in the background section, incorporating electricdrive (rather than mechanical-drive) technology into Navy ship-acquisition programs

could add technical or schedule risk to those programs, since electric-drive technology

is less mature than mechanical-drive technology for application on naval ships. The

potential amount of technical or schedule risk varies, depending on the exact

configuration of the system in question. More advanced approaches to electric drive

(e.g., those involving more advanced types of motors and motor drives) present

greater potential technical or schedule risk, but also promise greater potential cost

effectiveness.

In general, electric-drive components presenting potential technical or schedule

risk include, among others,

! motor drives – which some sources identified as perhaps the foremost item of

development risk,

! motors – whose development risk has been widely discussed,

! generators – if more advanced generator designs are pursued,

! the electrical distribution system,

! advanced propeller/stern configurations – if these are pursued, and

! overall system design and integration.

Issues to be addressed include:

CRS-42

! demonstrating at full scale technologies that to date have been demonstrated

at partial scale,

! improving thermal performance (i.e., preventing the overheating of increasingly

power-dense components),

! achieving desired levels of acoustic quieting and shock resistance, and

! designing overall system interfaces, controls, and module specifications,

particularly for achieving system modularity and commonality and built-in

potential for evolution and upgrades.

Some of the risks involved in developing electric-drive technology have been

mitigated by the successful development of electric-drive technology for commercial

ships. Some industry sources argued that the amount of remaining risk involved in

developing electric drive for Navy use is low to moderate, and that development of

electric drive poses less risk than has been posed by other technologies that the Navy

has successfully developed. Other sources suggested that the degree of risk may be

higher (moderate or even potentially high risk in some respects), particularly if the

technology is developed on an aggressive (i.e., compressed) schedule.

The degree of technical risk involved in developing electric drive might be

mitigated through more intensified research and development. Given the number of

specific development possibilities that currently exist in electric-drive technology, the

amount of research and development funding that until recently has been programmed

for the area, and the potential cost and warfighting benefits of electric drive, an

argument can be made that electric drive technology could be further elevated in

priority as an element of the Navy’s research and development account.

Electric drive, however, is by no means the only promising technology area for

the Navy. If the Department of the Navy’s overall budget (or its research and

development budget) remains relatively stable, applying significantly more funding to

research and development work on electric drive might come at the expense of other

promising Navy technology programs. The potential implications for other Navy

programs of providing increased funding might underscore the need for developing

an electric-drive technology investment roadmap and more precise and systematic

measures of the potential costs and benefits of electric drive technology.

Common System. As noted earlier, the Navy stated in its March 1999 report

to Congress that developing common electric-drive components is feasible for several

kinds of Navy ships and that pursuing electric drive technology in the form of a

common family of components could have advantages for the Navy.

The Navy and the other military services have used the concept of commonality

in numerous other equipment-acquisition programs over the years as a means of

satisfying operational requirements in the most efficient manner possible. To cite just

a few key examples, the Navy has long had common guns, missiles, weapon

launchers, radars, sonars, computers, communication systems and other electronic

systems that are installed across a variety of ship classes. In the area of ship

propulsion, a single type of nuclear reactor (the S5W) was once used to power

various Navy submarine classes, and a single type of gas turbine engine (the LM2500)

has been used as the prime mover for every class of major surface combatant that the

Navy has built since the 1970s. As the Navy has declined in size during the 1990s,

CRS-43

Navy leaders have placed even greater emphasis on achieving commonality of key

equipment across ship classes as a means of preserving economies of scale in

equipment development, procurement, and life-cycle operation and support.55

Potential advantages of a common electric-drive system (or a family of common

components) for application to both submarines and various surface ships include:

! nearer-term cost savings due to streamlining of research and development

costs (i.e., avoidance of parallel development of differing electric-drive

systems);

! both nearer- and longer-term savings due to greater efficiencies in procurement

(i.e., achieving maximum economies of scale in the production process by

producing larger numbers of a single system or family of components); and

! longer-term savings due to the streamlining of fleet training, operation and

support efforts (i.e., maintaining common training, maintenance, and logistical

support systems for all Navy ships equipped with the system).56

The potential nearer-term savings are difficult to estimate due to the scarcity of

precise and systematic cost estimates for researching and developing various potential

technical approaches to electric drive. On the basis of preliminary cost information

provided by sources for this report, however, it appears that the savings could easily

total in the millions of dollars, and could, depending on the potential scope of avoided

parallel development efforts, run into the tens or even hundreds of millions of dollars.

The potential long-term savings of pursuing a common system or family of

components are similarly difficult to estimate due to both the relative scarcity of

precise and systematic cost estimates for producing, operating, and supporting ships

equipped with differing forms of electric drive, and uncertainty concerning how many

classes of ships might be equipped with the technology, and when. Navy experience

with other major acquisition programs, however, suggests that longer-term savings

due to improved economies of scale in production and the streamlining of training,

operation and support systems could be substantial.

The concept of developing a common system or family of components poses at

least two potential policy issues for the Navy and Congress. One concerns the extent

of commonality across electric-drive-equipped Navy ships; the other concerns the use

of competition in the development and procurement of electric-drive technology.

55

See, for example, Schweizer, Roman. Requirements Chiefs Approve Plan to Focus

Common Technology Development. Inside the Navy, September 29, 1997, and Schweizer,

Roman. Requirements Chiefs Consider Pooling Money to Develop Common Components.

Inside the Navy, September 15, 1997.

56

For an article discussing the potential benefits of a common electric-drive system, see

Bartlett, E. L., Jr. Electric Propulsion: Commonality Is the Only Way. U.S. Naval Institute

Proceedings, August 1998: 71-73.

CRS-44

Extent of Commonality. The concept of developing a common electric-drive

system or family of components for all electric-drive-equipped Navy ships is

sometimes posed, tacitly if not explicitly, as an alternative to developing a different

electric drive system for each kind of Navy ship to be powered by electric drive.

These two approaches, however, are simply two options at opposite ends of a

spectrum of acquisition options that also includes mixed approaches that would

combine elements of commonality with elements of ship-specific solutions. One

example of a mixed approach would be to equip most types of ships with one kind of

electric drive system while equipping one or more other types of ships with a different

kind. Another example would be to install certain components as common elements

across the fleet while permitting other components to vary more fundamentally by

ship type. The Navy’s March 1999 report appears to suggest that the second of these

approaches may have merit.

Should agreement be achieved to broadly pursue electric drive, the goal for

policymakers would be to optimize the cost-effectiveness of electric drive as it is

applied across the fleet. Past acquisition experience clearly suggests that designing

a unique electric-drive system for each kind of ship would not result in the most costeffective application of electric drive across the fleet. Past experience, however, does

not prove conclusively that it would be achieved by an approach that would install a

common system or family of components on every kind of ship that is scheduled to

be powered by electric drive.

Just as there are numerous kinds of equipment in the Navy that are installed in

identical or near-identical form on various classes of ships, so too are there examples

of equipment that differ significantly in design from one kind of ship to the next.

Some cases of equipment differentiation across ship types are likely due to either a

reduced emphasis in previous years on achieving the benefits of commonality or

conscious decisions to continue operating non-conforming “legacy” systems on some

ships because these systems would be expensive to replace. Other cases of equipment

differentiation across ship types, however, might reflect a judgment that a maximally

common approach was not the optimum solution on a fleet-wide basis. In the case

of ship propulsion equipment, differentiation across the fleet in the past has resulted

from differences across ship types in factors such as ship size, mission, or operational

cycle.

From a public-policy perspective, commonality is not an end in itself but rather

a strategy that policymakers would consider as they sought the most cost-effective

path to apply electric-drive technology across the fleet. In seeking this path,

policymakers might wish to assess the relative merits of both a maximally common

approach and more mixed approaches. A technology-development roadmap or

master plan and more precise and systematic estimates of the costs and benefits of

various technical approaches to electric drive could keep the potential value of

commonality in perspective and help policymakers identify the best overall path for

the fleet.

Competition. If policymakers chose an acquisition strategy for electric drive

featuring maximal or near-maximal commonality across ship types, a second potential

issue to consider would be the role of competition in the development and

procurement of electric-drive technology. Pursuing a common electric-drive system

CRS-45

or family of components could in theory lead to the emergence of a dominant or

monopoly supplier to the Navy of electric-drive technology, components, and

systems. Such a development could inhibit if not preclude the Navy from using

competition in the development and procurement of follow-on electric-drive

technology.

In light of this possibility, policymakers who place a high value on the use of

competition in defense development and procurement – to secure benefits in

restraining cost, improving product quality, encouraging adherence to scheduled

delivery dates, and promoting innovation – might wish to consider measures aimed

at ensuring that the Navy’s acquisition strategy for electric drive makes maximum use

of competition among industry approaches prior to selecting an approach that would

form the basis for the common system. They also might consider actions aimed at

ensuring that nearer-term acquisition decisions, including the selection of a common

system or family of components, preserve, as much as possible, a potential for

employing competition in the eventual development and procurement of follow-on

electric-drive technologies, components, and systems.

One possible approach for preserving a potential for competition in follow-on

development and acquisition in electric drive would be to require the common electric

drive system to be designed to a so-called open architecture – a set of nonproprietary

and nonexclusive technical standards for key system characteristics that would permit

firms other than those making the current system to compete on an equal footing with

those making the current system for the development of follow-on technologies,

components, or systems. This approach is now being used in other defense

acquisition programs, particularly those involving electronic systems.

Another possible approach, not mutually exclusive with the previous one, would

be to provide some amount of support to firms other than those who supply the

current electric-drive system to finance continued development of potential competing

technologies or components that are currently considered less mature or more risky

than those used in the current common system. Providing such support would reduce

the research and development savings associated with pursuing a common electric

system or family of components, but would help bring to maturity alternative technical

approaches that could be more cost effective than those that can be pursued today.

Financially supporting potential downstream competitors and competing technologies

could maintain a wider set of alternatives and some degree of competitive leverage

for the federal government over the longer run as it sought to improve its electricdrive technology in step with technological advancements.

Motors. Much of the debate since 1998 over the application of electric-drive

technology to U.S. Navy ships concerns the type of electric motor that should be

used. Indeed, within the overall debate over electric-drive technology, perhaps no

one issue has been more contentious. The issue is highly charged because specific

motor types are associated with specific firms competing for a part of the Navy’s

electric-drive program. A preference for a certain motor type can thus lead to a

preference for the proposal of one firm or industry team over that of another.

As mentioned in the background section, the electric motors associated with

electric-drive systems for large ships can be divided into five basic categories –

CRS-46

synchronous motors, induction motors, permanent magnet motors, superconducting

synchronous motors, and superconducting homopolar motors. Each of these is

discussed below.

Synchronous Motor. Of the basic motor types considered here, the synchronous

motor can be considered the most mature technologically in application to large ships.

It is the type currently used on most electric-drive-equipped commercial ships,

particularly cruise ships, where it has been used successfully for more than a decade.

There is a consensus among both naval and industry sources that the

synchronous motor, if scaled up to the higher horsepower ratings needed to move

surface combatants and submarines at high speeds (i.e., 30+ knots), would be too

large and heavy to be suitable for use on these ships. The synchronous motor, in

other words, is considered insufficiently power-dense for application to these ships.

Space and weight is a critical design consideration in the design of submarine

propulsion plants. While space and weight considerations might be more relaxed in

the design of a surface combatant’s propulsion system, a high-horsepower

synchronous motor is considered too large to fit into a podded propeller.

The synchronous motor can be made somewhat smaller and more power-dense

through the application of water cooling (as opposed to air cooling). This approach,

however, appears to be receiving no attention in industry efforts to develop electricdrive technology for the U.S. Navy, perhaps because the potential gain in power

density is not deemed large enough to justify the effort.

The most likely apparent opportunity for incorporating electric-drive systems

using synchronous motors into the Navy’s electric-drive effort would be to install

them in large Navy auxiliary ships. Compared to surface combatants and submarines,

auxiliary ships are often designed for lower maximum speeds, their internal space

constraints may not be as great, and their propulsion systems might not need to meet

the same acoustic-quieting or shock-resistance standards. Consequently, it might be

feasible to equip auxiliary ships with commercial electric-drive systems using

moderate-horsepower synchronous motors that have already been developed for use

on cruise ships.

Using a commercially available electric-drive system on an auxiliary Navy ship

would raise an issue concerning the extent of commonality of electric-drive

technology on U.S. Navy ships. Equipping auxiliary ships with commercial systems

using synchronous motors would differentiate them from Navy ships using technology

developed specifically for U.S. Navy use and thus reduce commonality in electricdrive technology within the U.S. fleet. It would also, however, make these auxiliary

ships common in their electric-drive technology to cruise ships and other commercial

ships, and permit them to take advantage of the economies of scale that exist for the

production and life-cycle support for these systems, thus recouping at least some (and

possibly much) of the cost-related benefits that commonality within the Navy would

achieve. In addition, if future Navy auxiliary ships are built to more commercial (as

opposed to U.S. Navy military) standards of construction, which is an option of

growing interest to the Navy, it might be viewed as appropriate to equip these ships

with commercial (as opposed to military) electric-drive technology.

CRS-47

Since today’s commercially available electric drive systems are made by

European firms, using a commercially available electric-drive system on an auxiliary

ship could raise an issue regarding use of foreign-made propulsion technology on a

U.S. Navy ship. Using a European-made commercial electric-drive system on a U.S.

Navy ship might be viewed as acceptable in terms of contributing to a broader twoway U.S.-European trade in defense-related systems. Policymakers, however, have

traditionally been highly resistant to the idea of relying on foreign-made technology

in the construction of U.S. Navy ships (and many other major U.S. military platforms

and weapons), in part on the grounds that it introduces a risk that unforeseen

developments in a foreign country could delay or disrupt a U.S. shipbuilding program

or complicate efforts to support these ships once they are in service, particularly in

time of crisis or conflict.

Although U.S.-based firms involved in electric-drive technology development so

far have chosen not to develop competing systems engineered to commercial

performance specifications, commercial electric-drive systems in the future could still

be built and supported in the United States, either by a U.S. subsidiary of a European

firm or by a U.S. firm on license from a European firm. This could reduce any risk

associated with using a European-developed commercial electric-drive system.

Induction Motor. The induction motor is generally considered the second-most

mature motor type for application to large ships, after the synchronous motor.57 As

discussed earlier, it is the type of motor used in the Navy’s land-based full-scale

electric-drive demonstration system in Philadelphia.

The induction motor can be made significantly more power-dense than the

synchronous motor. Most of the sources consulted for this report argue (or do not

contest) that it can be sufficiently power-dense to be suitable for use on U.S. Navy

surface combatants. By the same token, however, most sources – including the U.S.

Navy in its March 1999 report to Congress – also argue (or do not contest) that the

induction motor is not sufficiently power-dense or quiet to be suitable for use on U.S.

Navy submarines.

Because the induction motor is generally considered more mature technologically

at this point than the permanent magnet motor or superconducting motors, using an

electric-drive system with an induction motor might help mitigate the risk of

integrating electric-drive technology into the DD-21 program. Since the induction

motor is not considered suitable for use on U.S. Navy submarines, however, using it

on the DD-21 would preclude achieving motor commonality across surface ships and

submarines in the Navy’s electric-drive program.

In addressing the commonality issue, one potential issue for policymakers would

be whether an electric-drive system for the DD-21 using an induction motor could be

designed so that it preserved commonality with submarines in components other than

the motor. Another would be whether the DD-21 system could be designed so that

57

The induction motor discussed here is sometimes called the advanced induction motor

to distinguish it from earlier, less sophisticated induction motors.

CRS-48

the induction motor could later be changed to a permanent magnet or

superconducting motor.

Using the induction motor on the DD-21 or other ships would similarly raise a

potential issue regarding use of foreign-developed technology, since this motor has

been developed by a European-based firm (Alstom) while U.S. firms are focusing on

developing permanent magnet and superconducting motors. As noted earlier,

however, Alstom is the supplier of the induction motor (and other components) of the

U.S. Navy’s land-based electric-drive demonstration system and has established U.S.based subsidiaries in Pittsburgh and Philadelphia to support its electric-drive efforts

for the U.S. market.

Permanent Magnet Motor. The permanent magnet motor can be made quieter

and significantly more power-dense than the induction motor – enough so that it is

consequently considered suitable for use on submarines as well as surface combatants.

As a consequence, the Navy and other sources generally agree that the permanent

magnet motor can be used in a common electric drive system for Navy surface ships

and submarines. As noted earlier, the Navy’s March 1999 report to Congress focuses

on the permanent magnet motor as the motor available in the nearer term that would

be suitable for a common electric-drive system. Both the 1998 NATO report and the

British Navy’s current advanced electric-drive development effort similarly focus on

the permanent magnet motor.

The permanent magnet motor is less mature technologically than the induction

motor, and consequently at this point may pose more development risk to incorporate

into a nearer-term ship-acquisition program such as the DD-21 destroyer. In contrast

to the induction motor, a version of which is being tested in full-scale form at the

Navy’s land-based test site, the permanent magnet motor will be tested in quarterscale (6,000-horsepower) form on LSV 2 (Large-Scale Vehicle 2), also known as the

Cutthroat – the Navy’s approximately one-quarter scale unmanned submarine for

testing technologies for possible use on the Virginia-class submarine and other future

submarines.58 The Navy’s decision to use a permanent magnet motor as the

propulsion system for this important test vehicle reflects a certain amount of Navy

confidence in permanent magnet motor technology, at least in quarter-scale form.

Sources differ regarding the amount of technical risk involved in scaling up the

permanent magnet motor to full size. Firms involved in developing permanent magnet

motor technology argue that the basic technological issues in permanent magnet

motors have been resolved, and that scaling up the technology will not pose any new

issues. Other sources, including firms involved in developing other types of motors,

demur, arguing that scaling up is never risk-free.

A key issue at this point is whether the permanent magnet motor will be

sufficiently mature for timely incorporation into the lead ship in the DD-21 class. The

Navy’s decision, announced in February 2000, to delay the procurement of the first

DD-21 by one year (to FY2005) will, other things held equal, reduce the risk

58

Costa, Keith J. Newport News, Electric Boat To Outfit Test Sub With Electric Drive.

Inside the Pentagon, February 25, 1999: 15.

CRS-49

associated with equipping the first DD-21 with an electric-drive system using a

permanent magnet motor. Under the previous plan to procure the first DD-21 in

FY2004, most sources agreed that the time line for developing the permanent magnet

motor for the lead ship would have been challenging. The additional year relaxes the

situation somewhat, though much will still depend on the intensity of the development

work that is conducted on the motor (which will depend in part on the amount of

funding applied to the work), and on whether unforeseen issues arise in scaling up the

technology.

If the permanent magnet motor is deemed not mature enough to install on the

first DD-21, then policymakers could face the issue of whether the later ships in the

DD-21 program should be built with the permanent magnet motor (when it matures),

and whether earlier ships in the program built that are built with a different kind of

motor (presumably an induction motor) should be backfitted with the permanent

magnet motor at some point during their life. Addressing these issues could involve

weighing the potential benefits of maintaining electric-drive component commonality

within the DD-21 class against the potential benefits of commonality between the DD21 class and other, subsequent, Navy ship classes that are equipped with electric

drive.

U.S. (as well as European) firms are developing electric-drive systems using

permanent magnet motor technology. The U.S. Navy can thus develop and procure

an electric-drive system using permanent magnet motors without necessarily raising

issues associated with use of foreign-made or foreign-developed technology.

As noted earlier, both the 1998 NATO report and the British Navy’s

development efforts focus to some degree on the transverse-flux version of the

permanent magnet motor, as opposed to the radial-gap version being developed by

U.S. firms. This raises a potential issue for Congress as to the relative risks and

merits of the transverse-flux and radial-gap versions, and whether the U.S.

development efforts should include more work on the transverse-flux version.

Supporters of the transverse-flux version believe it to be the most efficient design, but

some sources stated that it may pose greater development risks than the radial-gap

design.

Some sources for this report, particularly supporters of other motor types, raised

a particular technical issue regarding permanent magnet motors that they argued

poses an elevated danger in the event of an internal fault (i.e., a short-circuit) in the

stator windings – a problem that can occur in an electrical motor. The issue arises

because it is not possible in a permanent magnet motor, as it is in other motor types,

to turn off the motor’s magnetic field.59 This, they argued, creates the potential for

a permanent motor to act as a generator in the event of an internal winding fault,

particularly if the fault occurs as the ship is moving through the water at some speed.

59

In a permanent magnet motor, the magnetic field that interacts with the electrical flow

to create mechanical movement is created by permanent magnets that are built into the rotor.

The magnetic field thus continues to exist when electrical power to the motor is cut off. On

other motor types, the magnetic field is created as a product of electrical energy flowing

through the motor, and ceases to exist when power to the motor is cut off.

CRS-50

This situation, they argued, would create a flow of electrical energy that would be fed

by the motor back into the fault, exacerbating the damage caused by the fault.60

Supporters of the permanent magnet motor stated that they are well aware of

this issue. For most kinds of internal faults, they stated, it will not be necessary to

turn off the magnetic field, because these faults can be managed through the design

of the motor and motor controller. For one kind of fault (a turn-to-turn short), they

stated, an ability to turn off the magnetic field could be useful, but the permanent

magnet motor can cope with this fault by stopping or slowing its rotation through use

of the same dynamic braking action as would be employed in the first stage of a

“crashback” scenario.61 In sum, they argued that the issue of dealing with an internal

fault, while real, can be addressed through careful system design and operation.

Some sources for this report also argued that the long-term stability of the

material used for the permanent magnets is not proven in large-ship propulsion motors

and could lead to reliability and maintenance issues over the life-cycle of the motor.

Supporters of permanent magnet motors argued that permanent-magnet motors in

industry use have proven themselves reliable over lengthy operating periods in other

applications and that the careful motor design can make permanent magnet motors

easier to maintain than existing electric motors.

Superconducting Synchronous Motor. The superconducting synchronous

motor employs superconducting technology (including cryogenic equipment to cool

the superconducting wire down to the temperatures at which the wires become

superconducting) to achieve significantly stronger magnetic fields than nonsuperconducting motors. As a result, supporters of this motor type argue, the

superconducting synchronous motor, if developed, can be more power-dense – and

also quieter and more energy-efficient – than a permanent magnet motor.62 The U.S.

60

Electrical motors, which convert electrical into mechanical energy, can also, if

operated differently, act in the reverse manner – as generators that convert mechanical energy

into electrical energy. The sources argued that in the event of a winding fault, even when

electrical power to the motor could be cut off, the rotor would continue to spin for some time

under its own momentum. As the rotor, with its permanent magnets, continued to spin past

the stator, with its windings, an electrical current would be created that could flow back into

the winding fault, causing additional heat and damage to the motor. This scenario, some

sources argued, would be particularly relevant if the ship were moving at some speed, because

the ship’s continued forward movement would cause the now-unpowered propeller to rotate

as a result of the ship’s forward movement through the water. This rotation would be fed by

the propeller shaft back into the motor, causing the rotor to spin even longer than it would

simply as a result of its own momentum.

61

A crashback scenario is when the motor is commanded to go immediately from full

ahead to full reverse. In accomplishing this, the system employs dynamic braking, in which

electrical energy is drained from the motor so as to produce a reverse torque that helps bring

the motor to a stop.

62

See, for example, Whitcomb, Clifford A. Commercial Superconducting Technology

for Ship Propulsion. The Submarine Review, April 2000: 62-73; Kalsi, S., B. Gamble, and

D. Bushko. HTS Synchronous Motors For Navy Ship Propulsion. Paper presented at Naval

(continued...)

CRS-51

firm developing the superconducting synchronous motor – American Superconductor

– is doing so as part of a broader effort to introduce high-temperature

superconducting technology into the electrical power industry.

The superconducting synchronous motor is less mature technologically than the

permanent magnet motor. Most sources argue (or do not contest) that it cannot be

matured quickly enough to be installed at acceptable risk on the first DD-21.

Advocates of the superconducting synchronous motor, while not necessarily

disagreeing with the Navy about whether the technology would be ready for

installation the first DD-21, argue that the technology for this kind of motor has

progressed in recent years more than others might realize and that the time needed to

mature the technology may be less than others estimate.

One technical issue regarding the superconducting synchronous motor concerned

the cost, reliability, and survivability of its cryogenic systems. Supporters argue that

this issue has effectively been resolved through the advent of high-temperature

superconducting materials (as opposed to older, lower-temperature superconducting

materials) and improved cryocoolers (refrigerator-like devices) that have made it

possible to achieve the necessary amount of cooling without the need for using

expensive liquid-helium cooling systems.

Some sources for this report raised a second issue – the possibility that the

superconducting wire in these motors might degrade over long periods of motor use.

In response, supporters of superconducting motors argue that superconducting wire

has been extensively tested and that its durability is now being proven in the

commercial electrical power industry.63

The question is how quickly a superconducting synchronous motor might be

made ready for use, how this would depend on the cost and intensity of the

development effort that is undertaken, and how the technology might consequently

fit into a longer-range strategy for incorporating electric-drive technology into Navy

ships. The Navy has initiated a program to build and test a 1,000-horsepower proofof-concept superconducting synchronous motor.

According to American

Superconductor, such a motor can be built and tested by 2004. Upon completion of

this effort, the company says, a full-scale, 25,000-horsepower version could be

developed and completed by 2009, making it possible to have the motor enter service

with the fleet in 2012 – two years after the first DD-21 is scheduled to enter service,

and about the time that the first follow-on DD-21s would enter service. American

Superconductor says this estimated 10-year motor-development effort would cost a

total of about $90 million.

62

(...continued)

Symposium on Electric Machines, Annapolis, MD, October 26-29, 1998; Mulholland,

Maxwell, and Stuart Karon. Letter to the editor, U.S. Naval Institute Proceedings, February

2000: 20, 22.

63

For articles on the use of superconducting wire in the commercial electrical power

industry, see Browne, Malcolm W. Power Line Makes Use of a Miracle of Physics. New

York Times, November 3, 1998; and Spotts, Peter N. Electric Power Cables That Just Can’t

Resist. Christian Science Monitor, November 5, 1998.

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Superconducting Homopolar Motor.64 The homopolar motor, like the

superconducting synchronous motor, uses superconducting technology to achieve

stronger magnetic fields than non-superconducting motors. As a result, supporters

argue, this motor can be made more power-dense, quieter, and energy-efficient than

a permanent magnet motor. In addition, supporters argue, because the motor

employs DC current, rather than the AC current used by all the other motor types

discussed here, the homopolar motor permits the motor drive to be less complex and

thus less expensive than the motor drives associated with the other motor types.65

Because of its potential advantages, the Navy worked on developing the

homopolar motor for many years starting in the mid-1970s. This effort has been

continued in more recent years by General Atomics.

The homopolar motor, like the superconducting synchronous motor, is less

mature technologically than the permanent magnet motor. In addition to the issue of

the cryogenic system discussed above in connection with the superconducting

synchronous motor, the homopolar motor poses a second development issue

concerning the current collectors that transmit electrical power from the stationary

parts of the motor to the rotating parts. Supporters of the homopolar motor state that

solid-metal current collectors have been developed that are superior to the older

l

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