Designing a Destroyer for the 21st Century

21st Century

With innovative combat systems, hull design, and mechanical and electrical equipment, the DDGLX—a new guided- missile destroyer equipped with a high- energy laser weapon system—could be the multimission ship of the future.

Naval warships of the next century promise to be as different from today’s warships as Admiral Ray­mond Spruance’s ships at Midway were from Admiral Horatio Nelson’s naval vessels at Trafalgar. Technological developments will force ship designers to rethink many design concepts. As each new innovation matures, it will be integrated with existing systems in naval ships then being designed.

So what can the Navy expect the destroyer of the 21st century to be? Two other naval officers and I undertook a year-long ship design project to answer this question while attending the Naval Construction and Engineering Pro­gram at the Massachusetts Institute of Technology (MIT).¹ The result is a guided-missile destroyer equipped with a high-energy laser weapon system—the DDGLX.

The DDGLX design integrates a number of emerging technologies. It does not entail building a vessel and then pouring in as much technology as will fit. By analyzing the possible systems, both individually and collectively, synergism is realized in the DDGLX. It integrates many new advances in combat systems, hull design, and me­chanical and electrical areas.

Combat Systems: The high-energy laser weapon system f (HELWS) promises to be the next-generation medium- | range, close-in air defense weapon. The HELWS uses a I

chemical laser and an optically tracking director to engage targets with directed energy. Helium, oxygen, nitrogen trifluoride, and deuterium combine in a partially evacu­ated chamber to create the laser. The effluent mixes with seawater and JP-5 jet fuel and ignites downstream in a combustion chamber to maintain high flow rates.

Since the time of flight for a laser weapon’s directed energy is essentially zero, the HELWS can shift targets rapidly, a valuable capability in the anticipated high- density threat environment of the 21st century. There are, of course, disadvantages associated with the HELWS. A very big system, it requires space equal to about two 64­cell vertical launch system (VLS) launchers. Much of this space is occupied by pumps and laser chemicals.

The pumps either can be gas turbine driven or electric. Gas turbines must run anytime the ship is in a threat area in order to reduce response time. However, this requires lots of fuel. If electric pumps are employed, the pumps do not need to run continuously because they can start quickly. However, the electrical load needed to run the pumps during battle conditions could be very high. This electrical load would require most ships to have an addi­tional ship-service generator system.

Disposing of the chemical laser exhaust is another con­cern associated with the HELWS. Mostly seawater, it also contains small amounts of toxic gases and corrosive chem­icals. If not carefully ducted over the side and aft, the chemicals can be hazardous to personnel and materiel. The laser director’s arc of fire also can be obstructed by its own effluent discharge.

Improvements to the current state-of-the-art Aegis com- mand-and-control system, able to rapidly acquire, track, and engage air targets, are envisioned for the next-genera­tion warships. The Standard SM-1 missile currently re­ceives mid-course guidance from the SPY-1 multifunction phased-array fixed-antenna radars and then switches to semiactive homing provided by the AN/SPG-62 illumina­tion radar. An improvement to the SPY-1, called com- mand-all-the-way, eliminates the need for separate illumi­nators and provides command guidance to the missile all the way to the target. Solid-state electromagnetic trans­ducers at the array faces eliminate the need for large radar transmitters and wave guides. Redundant and fault-toler­ant computer systems on a data bus allow for the loss of one or more computers while still maintaining the “battle picture.”

Soviet advances in submarine detection technology con­tinue to alarm Western observers. If the Soviets reduce the intensity of their sound source, then two things could be done to maintain an adequate signal-to-noise ratio. U. S. ships must reduce their own noise and increase their array gain. A wide-aperture array, measuring about 100 feet by 20 feet, that only can be mounted along the hull, has been proposed. On most conventional ships, however, this puts the array outboard of the ship’s noisiest spaces, the main machinery spaces. In addition, the draft of most destroyer- size ships puts the top of the array too close to the water’s surface where wave action can affect the array’s opera­tion. A larger, bow-mounted array is also desirable, but

this creates serious drydocking difficulties for conve¹¹ tional monohulls.      ,

A heavy torpedo, like the Mk-48 submarine-launci

torpedo, is a better antisubmarine weapon than

the

smaller, over-the-side torpedoes. Although it would advantageous to launch the heavy torpedoes from a ⁵ face ship, there is not enough hull space in a monohu¹¹ install underwater torpedo tubes.

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The VS-22 Osprey, the ASW version of the new

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rotor aircraft, promises to have significantly more sp^e'

and range than current ASW helicopters. Unfortunai

tely:

very few combatants can provide the large flight deck hangar required for the Osprey.

Hull Design: The small waterplane-area twin

(SWATH) concept is not new, but it has yet to

-hul¹

be &

ployed in a combatant. The idea is to minimize

the

waterplane area in order to reduce the ship’s response

wave forces. In its basic form, a SWATH is a box

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pended above the water by two longitudinal struts ^

connect the box to two cylindrical hulls beneath

ocean’s surface. Since the two hulls interact as the

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passes between them, local high- and low-pressure reg¹^ exist along the hull. Contouring the hulls, or changing radius of the hull in selected locations along its l^£rl? j. significantly reduces the power requirements. The sf&

power curve for a SWATH typically has peaks and vai

because of this hull interaction. By fine-tuning the

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toured hulls, a valley can be shifted to the desired ^c

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speed and fuel requirements can be greatly reduced

The SWATH hull offers numerous advantages

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compared to a conventional hull form. The SWATH

better seakeeper because of reduced wave response

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longer pitch, heave, and roll periods. The semi-rec- . lar upper box creates more enclosed volume and a ¹ deck area. The axi-symmetric hulls provide a “^c*^e

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wake field that increases propeller efficiency and ret- noise, especially if the propeller is well aft of the ^s ^

Since the box, struts, and hulls are separate structures

designer has the flexibility to optimize the hulls for

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mum resistance, the struts for stability and seakeep¹ and the box for arrangement. Survivability also is bed

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a SWATH because redundant systems can be ^seP^a’_[Il0si

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monohulls, a SWATH can sustain a hit on the poo

port and starboard, as well as fore and aft. Unlike ⁿ\ ,₍

without damage to systems on the starboard side. ^ The SWATH has some disadvantages as well. ships have large beams and drafts because of their g^e°^ ₃ ric design. Weights and margins are also troublesom^e ^ SWATH design. To keep the box above the water, _t SWATH must maintain the same displacement throUg*¹ j

r

its service life. For this reason a SWATH must carry

ballast (like a submarine) or extra fuel to serve as the 'j^1.

if

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gin for future growth. Propulsion is also a challeng^e , ^ SWATH. Either the lower hulls must be big enoug ^ accommodate the entire propulsion plant, or power g^e j, ated in the box must be able to be transferred to the Pul­lers. Even though the SWATH has sufficient enclosed f ume, these arrangements can be difficult because n¹¹¹ jj_s, the volume is in the oddly shaped spaces in the

140

j(

Proceedings / Octob^cr

^ruts> and haunches. The haunches are the prism-shaped ^uctures at the intersection between the box and the strut ..¹ resemble a fillet and are used to compensate for the stresses in this region. In addition, the threat of off- u_Se'^er ^°°d'ⁿg in the hulls or struts forces the designer to ^eclosely spaced, transverse, watertight bulkheads. The ^ain machinery is particularly difficult to arrange in ^a|-^es having small fore-and-aft dimensions. Placement (L ”^e rudder is also a problem for SWATH ships because h_a^e Propeller must be aft of the hull. Finally, SWATHs Uj ,^e higher calm-water powering requirements because of ^lr large wetted surface and friction drag.

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^^echanical Systems: Active fin stabilizers are used ^ay in monohulls to reduce roll and in SWATHs to re­Pitch. With an appropriate control system these fins

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_rij ^can be used for steering, eliminating the need for f_ln ^ers- Low-speed maneuverability is poor because these f_t ^{S are} not in the propeller race where they can benefit pro*^{11 was}h> but differential thrust from widely spaced Pdlers more than compensates. ^ae intercooled regenerative gas turbine cycle uses a

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dad ^seawater heat exchanger called an “intercooler” ^Ua large

_er heat exchanger called a “recuperator to tn- n, ^Se fuel efficiency by nearly 30% over conventional l^^rine gas turbines.² The intercooler cools the intake air Th'^Veen the low-pressure and high-pressure compressors. ^cha ^recuP^erator preheats combustion air through heat ex- tj_v ”^e with hot exhaust gases. The intercooled regenera­te^ §as turbine also significantly cuts back the tempera- tM °f the exhaust gas, which n^^Ccs the ship’s infrared sig- c_0Qj^e- The weight of the inter- rn_0r.^ers and recuperators is the ^{6 taan} compensated for by Deduction of fuel required.

propulsion motors, making this a prime example of an integrated electrical system.

Electric drive makes it possible to isolate the relatively noisy engines from the water. Only the quiet electric mo­tors are in the hulls, resulting in less radiated noise.

System Integration: The large beam associated with the SWATH hull form provides athwart-ship separation for redundant systems. It also allows adequate flight deck and hangar space for the Osprey. The deep draft also puts the wide-aperture array below wave action.

Since the main engines are in the box, the midsections of the underwater hulls are free of noisy machinery. The bows of these underwater hulls resemble those of subma­rines, and a large spherical array would fit nicely in the bow of each hull without causing drydocking difficulties. Removing machinery from the hulls also leaves room for two Mk-48 torpedo tubes in each hull, and the contours in the hull allow the tubes to be canted to the outboard side.

The oddly shaped spaces in the hulls, struts, and haunches are perfect for tankage space required for the fuel that serves as the growth margin. In fact, there is so much room for tankage that the DDGLX carries more

^v°lu,

^ is needed.

t_et^^!eS^rated Electrical Sys- driv_e Super-cooled electric P^rov*des an efficiency d_ard^erally comparable to stan- &a_r, Echanical reduction f)_e3. with the arrangement V^’ty necessary for a f_0r j Tl design. Electric drive allows b^nsverse mounting of the gas tur- '"ore 'ⁿ k°^x' Cryogenic cooling is C(w ^efficient and can tolerate smaller ro_0t^ponent sizes than conventional <T^{rs a}nd generators. ^cVc| ^'^s controlled by a solid-state sjg ^c°^nverte^r that receives an input the r ^^r°^m ^e pilot house and alters drivj ^re1^Uency ^op the electrical power thr_e ® the propulsion motors. Large

Phase transformers reduce the voltage of this power service use. And in a casualty mode, the ship- gas turbine generators can provide power to the

^ln8s / October 1988

141

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derwater hulls, two spherical bow-mounted sonar arr^a^ .

e

(MIDAS) system, a Seafire gunfire-control system- ^aI1'

SLQ-32 electronic countermeasures system.

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margin), and every fuel tank has an identical empty tank ready for clean ballast when the fuel is consumed. The DDGLX carries enough fuel that, as delivered, the endur­ance range will be in excess of 10,000 nautical miles. The haunches may not be suitable for workshops or maga­zines, but they are adequate for the oxygen, helium, and deuterium cylinders, and fresh water cooling pumps re­quired for the HELWS.

Closely spaced, transverse bulkheads make engine- room arrangements difficult, but electric drive allows transverse mounting of the gas turbines and the flexibility of putting switchboards in adjacent spaces. The super­cooled motors are small enough to be placed well aft in the tapered section of the underwater hull. This results in short shafts and large physical separation from the wide-aper- ture array. The integrated electric system can provide the peak load of the HELWS electric pumps without an addi­tional generator. The ship may slow a knot or so during antiair warfare engagements, but full speed can be re­stored seconds after firing the HELWS.

Fins would be mounted between the hulls to reduce roll and pitch, as well as steer. This arrangement allows for the use of large fins without increasing the ship’s maximum width or making it necessary for the fins to retract. No rudder is required, and low-speed maneuvering is not a problem because of the large separation between the pro­pellers. Differential thrust or opposing screws provide good low-speed maneuverability. The propulsors on the DDGLX are separated by nearly 80 feet.

The SWATH’s increased power requirement in calm water is partially offset by the intercooled regenerative gas turbine’s greater fuel efficiency. The lower exhaust tem­perature is an additional benefit. The DDGLX takes the infrared signature reduction one step further by installing an exhaust-diversion valve. This allows the ship’s com­manding officer to divert the gas turbine exhaust between the hulls when there is an infrared threat. Exhaust also can be directed through the stack in high sea states, to prevent back flow that could harm the engines, or while prosecut­ing a submarine contact.

The SWATH hull form has another advantage. The

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directors. The DDGLX also diverts VLS exhaust bet"'^21-1 the hulls for the same reasons.  _

These systems, together with an improved Aegis ^c°ⁿ’ mand-and-control system, form the very capable weap¹ system that is the heart of the DDGLX.

The DDGLX: The design of the DDGLX began wi^ mission analysis. The designers wanted an ASW plat'⁰ capable of conducting extended operations in the north^e latitudes, taking the fight to the enemy, and defe"⁰¹^ herself or a carrier battle group. From this mission can'¹- ‘ payload and requirements for seakeeping and enduran^L The SWATH module of the advanced surface ship eva'¹^ tion tool (ASSET), a computerized ship-design p^r°S^r^.J then was used to develop the initial baseline ship- ASSET output was verified by various means, inclu⁰' - computer models, analytical formulas, and the SWA ^ experts at Naval Sea Systems Command and the Taylor Research Center. The characteristics of DDGLX in its final form are presented in Table L The DDGLX is armed with a 64-cell VLS forwaT > 32-cell VLS aft, two HELWSs, two Mk-45 5-inch^ caliber lightweight guns (mounted port and starboa' two Vulcan Phalanx close-in weapon systems, four un water-launched torpedo tubes, and two VS-22 Osp ASW aircraft.

The sensors include four SPY-1 phased-array faces with the command-all-the-way and solid-state ^trJ , ducer improvements, a rotating phased-array ^a°J^u radar, two wide-aperture arrays on the midsections ot

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two towed arrays, a mine detection and avoidance =

Mobility is provided by four 26,500-horsepower¹¹ . cooled regenerative gas turbines driving four M helium-cooled, 6,900-volt, Alternating current (AC) 8 j erators. Liquid-helium-cooled AC motors turn two du propulsors. The propulsion system is integrated wim ship-service electrical system using 6,900V/450V

142

Proceedings / Octob^er

Two 1,000 kilowatt ship-service gas turbine gen­, ‘‘tors

tol| *'^{ns w}'^t^ ^an active-control system reduce pitch and

^irUst,

^ers, mounted in the forward contour of the underwa-

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labi ^FS P^rov'^ti^c backup ship-service power. Four control- ^e fins with an active-control system reduce pitch and as well as provide directional control. An integrated djff ^euvering control system makes use of the fins and stg ^erential propulsion thrust to provide “one-knob” (L ^r,n8 and speed control. Two 1,000-horsepower Omni-

m, ^ls, assist in docking maneuvers and provide a five- emergency propulsion system.

_Sey^ne DDGLX remains operational through sea state |_ec.^et1’ an improvement over current destroyers. A full col- b_io,^1Ve Protection system protects the crew from chemical, nJSKBl, or radiological attacks. A distributed com- 'aid-control system allows loss of the combat infor- >°n center without total loss of combat capability.

options in the Persian Gulf demonstrate the diversity ^^reat faced by modem warships. Not only are sur- ^S^'P^S facing enemy aircraft, missiles, submarines, _St°‘her surface ships, the threat also includes mines, jn_st boats, chemical weapons, and terrorist acts. And itig .^as file scope of the threat is increasing, defense spend- k ^ °ⁿ the wane. So, as in the past, we are called upon it_Cc ^triore with less, and technology becomes the key to ^0lHplishing this task.

With limited means and global commitments, ships in the next century will be called upon to perform more inde­pendent and small surface action group operations without the protection of a carrier and her air wing. Ships that cannot defend themselves or carry out their mission repre­sent dollars poorly spent. Fewer numbers of technologi­cally advanced ships with superior warfare capabilities are preferable to larger numbers of ships with only moderate capabilities.

The DDGLX is a ship capable of long-term independent operations under adverse conditions with impressive fire­power. It exploits the synergism gained by using several innovative concepts. The DDGLX is the type of multimis­sion destroyer required for service in the next century.

'Lieutenant Commander Richard Hepburn, U. S. Navy, Lieutenant James Luchs, U. S. Navy, and I conducted the DDGLX design project discussed in this article. ²T. Bower and D. Groghan, "Advanced-Cycle Gas Turbines For Naval Ship Pro­pulsion," Naval Engineer’s Journal, May 1984, pp. 262-271.

Lieutenant Spencer is a ship superintendent at the Long Beach Naval Shipyard. He recently completed graduate course work in naval con­struction and engineering at MIT. He graduated from the U. S. Naval Academy in 1980, and served as the combat information officer on board the USS Mount Vernon (LSD-39).