Navy and Industry Pursuing New Power and Propulsion Methods

By Edward Lundquist

Alion Science and Technology

Advanced Materials, Manufacturing and Testing IAC, Rome, NY

The AMMTIAC Quarterly, Volume 4, Number 1

Powering the Future Force

New Power & Energy Technologies for the Warfighter

The Navy is testing new concepts in power generation, conversion,

and distribution to make ships more efficient, economic,

and combat-effective. Ships being developed in both the near

term and long term will have a variety of newly designed

propulsion systems depending on their size, mission, and ship

characteristics. This article discusses some key technologies on

the horizon.

ALL-ELECTRIC INTEGRATED PROPULSION

An integrated power system (IPS) is an all-electric architecture,

providing electric power to the total ship with an integrated

plant. IPS enables a ship’s electrical loads, such as pumps and lighting, to be

powered from the same electrical source as the

propulsion system (e.g., electric drive), eliminating

the need for separate power generation capabilities

for these loads.  To meet the increased power demands for new

sea-based weapon systems, next-generation surface

combatants, such as the DDG 1000 Zumwalt-class

of guided missile destroyers (see Figure 1), will feature

all-electric propulsion and an entirely new way of

distributing power for propulsion, ship service, and combat

capability. All-Electric Propulsion is a promising technology for

both naval and commercial marine applications. On the DDG

1000, power will be generated by two large gas turbine generators

and two smaller ones. By using efficient power management,

power is available to handle all of the electric loads throughout

the ship, including potential future power-hungry weapons such

as rail guns or directed energy weapons.

The combat value of an electric ship goes well beyond weapon

capability and capacity. There are significant efficiencies and

redundancies. At full power, DDG 1000 will achieve speeds up

to 30 knots. If one of the main turbines is lost, the plant can

be isolated and still achieve 27 knots. Since a warship usually

cruises at reduced power once it has arrived on station, normal

station-keeping can be accommodated with the two small

turbines to save fuel and reduce radiated noise. The power previously

trapped in the propulsion train can now be directed to

enhance combat capability and mission flexibility. At lower

speeds, Zumwalt has a surplus of power that can be made available

as needed. Further advantages include the elimination of maintenance-

intensive and hightemperature auxiliary steam systems, reduced noise

and vibration, and better fuel efficiency.

Among the major advantages of electric drive for naval ships is that the prime movers, whether gas

turbines or diesels, do not need to be located in a central machinery space or

mechanically connected to the propeller shaft as with

traditional propulsion systems.

Instead, the engines can be located anywhere

in the ship, distributed throughout the hull, and connected to

generators to supply power. This power can be fed to a central

bus that can be used for propulsion.

An all-electric integrated propulsion system enables more

design flexibility in terms of engine placement. For example,

the engines can be placed in the bow, stern, or even in the

superstructure for smaller engines. One of the advantages of

distributed power in a warship is survivability. If an engine incurs

damage or is incapacitated in one part of the ship, that part of

the distribution system can be isolated while power can still be

generated and distributed throughout the rest of the system. The

DDG 1000 will be powered by Rolls-Royce MT30 gas turbines,

which is based upon the Rolls-Royce “Trent” engine that powers

the Boeing 777 airliner. The aviation version of the engine has a

demonstrated reliability of 99.98%. The ‘marinized’ version of

the MT30 has 80% commonality with the Trent 800 but is

shock-mounted and has different blade coatings for operation in

a saltwater environment. This engine is also serving today aboard

the new Littoral Combat Ship USS Freedom (LCS 1). Zumwalt

will also have a smaller gas turbine, the Rolls-Royce 4500.

DDG 1000 power generators produce 4,160 volts alternating

current (AC), which is rectified to direct current (DC) that

allows ship service power distribution to be tailored to the ship’s

needs. There are three primary advantages to DC. First, DC uses

solid state power conversion that supplies loads which are converted

back to AC and is a cleaner way to supply power.

Secondly, many of the combat systems’ loads are DC. Finally, it

enables power to be shared and auctioned. DC enables uninterrupted

power even in the occurrence of a casualty.

The DDG 1000 will employ fixed pitch propellers.

Controllable pitch propellers and their associated complex

hydraulics are not required since the motor, and thus the shaft,

can be electrically reversed. But novel approaches to propulsion

are being considered for future combatants.

Other new naval ships are also adopting integrated electric

power systems. The next-generation CVN 21 aircraft carrier,

the USS Gerald Ford (see Figure 2), will have a newly designed

nuclear power plant and all-electric systems and propulsion.

The next amphibious assault ship, the USS Makin Island (LHA

6), will feature a combined gas turbine and electric propulsion

system.

The surface combatant IPS propulsion engineering development

model (EDM) for DDG 1000 is being tested at the Land-

Based Test Site (LBTS) at the Ships Systems Engineering

Station in Philadelphia. The test site has been used to evaluate

different configurations and motors. The test program validates

key system metrics such as torque, speed and power output, and

specific fuel consumption for the various configurations.

The Navy has tested the 18-megawatt (MW) advanced induction

motor (AIM), which will be the baseline for DDG 1000,

produced by Alstom at the LBTS. This is essentially the same

system installed on the Royal Navy’s new Type 45 destroyer, the

HMS Daring, which has just been commissioned. The IPS

features Integrated Fight through Power (IFTP), a fully automated

DC Zonal Electric Distribution System (DC ZEDS) that

provides flexible, reliable, high quality power to all shipboard

loads. Other configurations are also being tested. The IPS system

is fully automated with little operator intrusion. The testing at

the LBTS will validate that the DDG 1000 IPS will automatically

take appropriate corrective action if there is a malfunction or

casualty without the input of an operator.

Engineers at the LBTS have also tested a 36-megawatt permanent

magnet motor (PMM). PMM has greater power density

than the AIM and may be used in future ships.

Many studies were performed on different combinations of

gas turbines. The purpose was to avoid development of new

gas turbines that were not qualified and in service or on their way

into service.

Although there are advantages to distributing the power system

throughout a warship hull, the size and weight of the various

components has usually necessitated keeping the propulsion

equipment low in the ship for stability reasons. The DDG 1000

engineering plant layout is relatively conventional because of the

air intake, exhaust, and drive arrangement.

DRS Technologies and General Atomics Electromagnetic

Systems are developing a hybrid electric drive which permits a

smaller service gas turbine to power a permanent magnet motor

that can power the ship at slow or “loiter” speeds. Using a smaller

turbine can result in significant fuel savings. Furthermore, the

motor can be reversed to function as a generator when propulsion

gas turbines are online.

Overall, integrated electric drive offers ship designers and

operators a plant flexibility that does not exist with mechanical

drive systems. However, trade studies must be used to select the

appropriate power and propulsion system for each ship.

There are some ships with partial electric drive or hybrid electric

drive mechanical drive systems. These include the operational

Type 23 frigates; the European Multi-Mission Frigates

(FREMM), a joint program between France and Italy, which are

now in construction for France, Italy, Morocco and Greece; and

the amphibious assault ship USS Makin Island (LHD 8), now

undergoing trials.

Despite the advantages, there are not a lot of electric drive

warships in service. The new generation of electric ships has yet

to prove themselves. The DDG 1000, Royal Navy Type 45, and

T-AKE propositioning ships are examples of all-electric warships,

but they are still in the design phase, under construction, or

just entering service. Even though there is significant interest in

electric drive systems, there are only a relatively small number of

ships actually under construction and in operation.

SUPERCONDUCTING MOTORS

American Superconductor and Northrop Grumman have

recently tested a 36.5-megawatt high-temperature superconductor

(HTS) ship propulsion motor at the LBTS. The motor uses

HTS wire that can carry 150 times more power than copper

wire used in more conventional motors. The advantage is more

compact propulsion systems which have greater power density.

Superconducting wire can carry more current and generate

higher magnetic fields in very small areas and thus can result in

a significantly smaller motor. In other words, more power is

available from smaller, lighter motors. That means Navy ships

can carry more fuel and munitions and have more room for

crew’s quarters and weapon systems.

General Atomics’ (GA) superconducting DC homopolar

motor for propulsion applications is small and light compared

to traditional and superconducting AC motor systems. This

motor uses low-temperature supercooling that employs gaseous

helium to maintain the superconducting wire within the motor

at 5 Kelvin, which is almost absolute zero. Since some materials

are much better conductors at very cold temperatures, and with

virtually no electrical resistance supercooled conductors make

for much more efficient motors. A comparable high-temperature

supercooled system operates between 40 and 75 Kelvin,

depending upon the technology chosen. Refrigeration at higher

temperatures is easier, but the high-temperature superconducting

material is not as easy to produce and is much more expensive

than the superconducting niobium-titanium wire in the

low-temperature motor. Niobium-titanium wire is the most

widely used and available superconducting wire in world-wide

commercial applications.

GA has built a 5,000 horse-power (HP) motor which is

4.5 feet in diameter. This technology is slender, light, and fuelefficient

and can be more readily adapted to propulsion pod

applications.

Additionally, while superconducting AC motors have similar

costs to the superconducting DC motor, there is no need for

power inverters and the associated electronics to switch DC to AC.

Propulsion Pods

Most marine motor applications are located within the hull and

coupled to a shaft to turn a propeller or waterjet impeller. Electric

power can also be used for propellers or waterjets but can also

power propulsion pods, which can be located outside the hull.

Pods provide better maneuverability to ships entering and

leaving port or maintaining a precise station. With a significant

amount of propulsion equipment located outside the hull, more

room is available inside the ship for other purposes. Also, the signatures

could be mitigated if the propulsion system was isolated

inside the hull.

Cruise ship pod systems, such as “Mermaid” from RRAB (a

joint venture with Rolls-Royce AB and Alstom) and ABB’s

“Azipod” systems, can rotate 360 degrees and eliminate the need

for rudder assemblies.With a pod, the motor is in the pod, while

an azimuthing thruster has the motor located in the hull. The

Royal Navy’s Echo-class of survey vessels uses electric azimuthing

thrusters. Pods were considered for Zumwalt-class ships but

ruled out because of their size.

The US Navy has used Small Water Plane Area Twin Hull

(SWATH) ships for research and surveillance. These catamarans

have long and slender motors and other propulsion

equipment located in the submerged cylindrical buoyant hull

sections, but prime movers can be mounted above the waterline.

ThyssenKrupp’s Nordseewerke has built the SWATH

research vessel Planet for the German Federal Office of

Defense Technology and Procurement. Planet will assess new

propulsion technologies and evaluate the sea keeping characteristics

of the SWATH hull form. Its electric propulsion

enables it to test mine detection and undersea warfare systems

and countermeasures.

Siemens in Germany is finding improved power availability

and system responsiveness with high-temperature superconductors

for podded waterjets applications. Siemens is also

developing fuel cell technology for ship propulsion.

Waterjets

While not a new form of propulsion, waterjets have not been

used on larger ships until recently. They present some clear

advantages for warships. Waterjets deliver rapid acceleration and

can sustain high speeds. Waterjet-powered ships are extremely

maneuverable and can stop quickly. They offer simplicity. The

flow is constant in a single direction. Engine loading is constant,

regardless of vessel speed, and waterjets do not overload the

engines. There may be no need for a gearbox. Astern propulsion

is applied by means of deflectors that divert the jetstream forward.

Precise station keeping can be maintained with waterjets.

There are many advantages of waterjets. The most prominent

advantage is the shallow draft of the system. Waterjets do not

have appendages (such as propellers, shafts and struts, or rudders)

that extend below the waterline. This minimizes the risk of

damaging the propulsion gear from grounding or from hitting a

submerged object, and it also reduces the maintenance requirements.

As a result the boats can operate close to the shoreline,

land on a beach for deployment of troops or equipment, or even

run over submerged logs or sandbars without damaging the

propulsion equipment. In addition, floating debris (such as

ropes, nets, or weeds) does not pose much of a risk to the system

particularly at high speed. Even though these items may be

drawn into the jet unit at slow speeds, they are unlikely to cause

damage and can easily be removed.

Waterjets are reliable. Like propeller-driven ships, there is still

a shaft but it turns the pump impeller at a constant speed as

compared to a much larger propeller. Drive shafts, gear boxes,

and engines receive less stress, thus prolonging their service lives.

The entire propulsion system requires less maintenance.

Waterjets are more efficient at higher speeds, particularly in

multiple drive installations such as catamarans. With no underwater

appendages, there is no increase in hull resistance as speed

increases or more drives are added. Efficient operation can also

be achieved over a broader range of speeds compared to propellers.

Waterjets cannot overload an engine due to excess boat

weight, towing, or extreme seas because they operate independently

of the body of water under a boat.

A fast vessel needs a relatively higher amount of power than a

slow vessel, and waterjets can provide a relatively large amount of

power despite their relatively small size. Conventional propulsors

would require relatively large propeller diameters.

A clean hull design, free of appendages, delivers greater speed.

Drag resistance increases significantly as ship speed increases.

Therefore, the absence of appendages becomes increasingly

important as ship speed requirements increase.

The Office of Naval Research (ONR) uses an experimental

130-foot-long craft called the Advanced Electric Ship

Demonstrator (AESD) to test various waterjet-based propulsion

configurations at the Navy’s Acoustic Research Detachment at

Lake Pend Oreille, Idaho. ONR engineers achieved improved

efficiency and maneuverability with a smaller, lighter propulsion

system while reducing noise at the same time. Named Sea Jet (see

Figure 3), the craft is essentially a quarter-scale model of the

DDG-1000 destroyer. It has been used to test an AWJ-21 underwater

discharge waterjet from Rolls-Royce Naval Marine, Inc.,

to validate better propulsive efficiency, reduced acoustic signature,

less drag, and better speed as well as improved maneuverability

for future surface combatants by eliminating rudders,

shafts, and propeller struts.

Sea Jet has also been employed to demonstrate the General

Dynamics Electric Boat RIMJET propulsor, which is a podded

system that features a permanent magnet motor to power a

propeller in the rim, rather than the hub, of the pod. The system

uses sea water for coolant, which eliminates the typical

elaborate cooling system consisting of pumps, piping, and heat

exchangers.

ONR has also developed an Advanced Hull Form Inshore

Demonstrator (APHID) which is testing a complete electric

podded propulsion system. The Rim-Driven Propulsor Pod

(RPD) uses a Pulse-Width Modulated (PWM) motor drive system

mounted on the Hybrid Small Waterplane Area Craft

(HYSWAC). Called Sea Flyer, the HYSWAC is built from a

modified Navy Surface Effect Ship and uses a Vericor TF-40 gas

turbine prime mover. Sea Flyer features an underwater lifting

body ship that combines the high-speed capabilities of a hydrofoil

and the rough-water stability of a small waterplane area twin

hull (SWATH), so it delivers higher speed and improved stability

over comparably sized vessels.

Cost can be an initial disadvantage of waterjets. They are

expensive to purchase and maintain. Waterjets are made from

costly stainless steel, which is more expensive than other propulsors

that are typically made from copper alloys. However, waterjet

lifecycle costs are relatively lower. Waterjets are less prone to

impact damage, and reduced engine stress results in less engine

maintenance and longer engine life.

The Littoral Combat Ships (LCS) will employ waterjets.

Waterjets were chosen for LCS to provide high speeds in shallow

waters, where the LCS will operate to combat asymmetric antiaccess

threats in the littoral regions of the world. Two variants

of LCS are being built. Lockheed Martin has delivered the

USS Freedom (see Figure 4), a semi-planing monohull design

built at Marinette Marine in Wisconsin. General Dynamics is

building a trimaran, the USS Independence, at Austal USA in

Mobile, Alabama. Both will have diesels and gas turbines, and

both will employ waterjets. The General Dynamics LCS has four

steering and reversing waterjets, while the Lockheed Martin LCS

has two steering and reversing and two booster jets. Both ships

displace about 3,000 tons and up to 4,000 tons fully loaded.

This will make the two LCS combatants the largest naval waterjet-

powered warships.

While the two versions have taken different naval architectural

approaches to the mission, both “seaframes” will carry mission

modules that can be reconfigured to adapt to each ship’s combat

mission assignment.

USS Freedom is powered by two Rolls-Royce MT30 36 MW

gas turbines and two Fairbanks Morse Colt-Pielstick 16PA6B

STC diesels. The seaframe is based on the Fincantieri-built,

Donald Blount-designed high-speed yacht Destriero, which

holds the record for the fastest transatlantic crossing (60 knots).

The 378-foot Freedom has a steel hull with aluminum superstructure.

The two 36 MW gas turbines and two diesel engines

power four large Rolls-Royce Kamewa waterjets. Four Isotta

Fraschini Model V1708 ship service diesel generator sets provide

auxiliary power.

USS Independence, the slender stabilized trimaran monohull

built by the General Dynamics team, has an overall length of

418 feet, maximum beam of 93 feet, and full load displacement

of 2,637 tons. The seaframe is based on Austal’s design for the

Benchijigua Express passenger and car ferry. Two General

Electric LM2500 22 MW gas turbines and two MTU

20V8000M90 9100 kW diesel engines are the prime movers,

powering four large steering and reversing Wärtsilä-Lips 2 X

LJ160E and 2 X LJ150E waterjets. With all propulsion flat out,

the Wärtsilä-Lips waterjets together expel roughly 27,000 gallons

of seawater per second exiting from the jet nozzles at a speed

around 90 mph. The trimaran variant built by General

Dynamics will also have a retractable azimuth thruster.

CONCLUSION

One design is not optimum for all situations. Cruise ships with

large portions of their itineraries at low power benefit from electric

drive. Fast ferries, which go to full throttle as soon as they

clear the breakwater and remain at full throttle until they reach

the next port, would be at a disadvantage with electric drive.

There are advantages to a mechanical drive system. Mechanical

drive systems are more efficient compared to electric drive systems

in terms of their ability to transmit energy from the prime

mover to the propulsor. For example, the mechanical drive is

estimated to transmit approximately 98% of the energy from the

prime mover output shaft to the propulsor. The electric drive is

estimated to transmit between 91% and 93%.

ACKNOWLEDGEMENTS

The author would like to thank Mike Worley, Vice President

of Naval Marine Programs for Rolls-Royce North America;

Mike Collins, former Program Manager for Integrated Power

Systems with Program Executive Office–Ships (PEO Ships);

Read Tuddenham, General Electric’s Manager of Integrated

Propulsion Systems and New Applications; Michael Reed,

Senior Vice President for Advanced Technology with General

Atomics Group; Tony Kean of HamiltonJet, Christchurch, New

Zealand; and Marit Holmlund-Sund of Wärtsilä.

Captain Edward H. Lundquist, US Navy (Ret.), is a Senior Science Advisor with Alion Science and Technology, Washington, DC. He is a senior-level communications professional with more than 24 years of public affairs, public relations, and corporate communications experience in military, private association, and corporate service. During his 24-year naval career, Mr. Lundquist qualified as a Surface Warfare Officer and later served as a Public Affairs Officer. He retired from active duty in 2000. He currently supports the Director for Surface Warfare on the staff of the Chief of Naval Operations. Lundquist currently is member of the executive committee for the Surface Navy Association, and serves as vice president of the Greater Washington Chapter. He is an Accredited Business Communicator (ABC) and the vice chair of the International Association of Business Communicators Accreditation Council. Lundquist is a graduate of Marquette University in Milwaukee,Wisconsin and holds a master’s degree in journalism and public affairs from the American University inWashington, DC. He writes frequently for publications including Armed Forces Journal, Unmanned Systems, Naval Forces, Warships International, Maritime Reporter, and others.

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