A Capable, Affordable 21st-Century Destroyer

W I L L I A M J. L E V E D A H L

A Capable, Affordable list-Century Destroyer

T H E A U T H O R

V !he assistant for technology in the Machinery Research and

De-• eiopmeni Diccoraie of rite Naval Surface Warfare Center. Carde--ock Division. Annapolis. Md. .After a 50-mission tour as a P-51 '-liistang pilot he received a B.S. in General enoineenng from MIT -md was elected to Sigma Xi. He subsequently studied gas turbines :nd aeronautical engineering at the Federal Polytechnic Insdtute . Zurich. Switzerland, and as a National Science Foundation fet-.ow he received his Doktor Ingenieur at ttie Technical University

•r .\achen. Germany. He conducted basic research in combustion Jl the National Bureau of Standards, and was head of advanced :ore design at the Knolls .atomic Power Laboratory (General Elec-:ric) during the 1950s when tiie currently used reactor cores were .lesigned. He then joined Combustion Engineering as chief project jnysicist In the design of central-station reactors. Subsequently, he lecame manager of research at Martin Marietta, involved largely :n direct energy conversion for outer space, fn 1970 he joined the -.nnapolis Laboratory to establish the Superconductive Electric Propulsion Program, and in 1974 assumed his present position. He has received ihe Disnngiiisiied Flying Cross, the Meritorious Civilian Service .Award. 10 patents, and Is the author of many tech-nical papers.

A B S T R A C T

A simple tumbleliome hull of 4S00LT lightship displace-ment carries 1200LT of military payload ÓOOONMi at 20kts with inherently-low acoustic, i n f r a r e d , and radar signatures, and with superior seakeeping, without seawater ballast. Its two intercooled, recuperated turbines replace the seven simple-cycle engines of a comparably-armed conventional destroyer and consume 59% less fuel; both ships share a 30kt sustained speed at 80% power. Use of stern flaps permits carrying more t'uei; range is doubled to 12,000 N M i .

Two removable, prealigned and pretested steerable propul-5or modules are attached to the stern after construction and are pierside replaceable without drydocking; each includes a iteerable pod aligned to the water inflow. Contrarotating trac-tor propeilers are driven by a pretested integrated capsule .vhich comprises seals, thrust bearings, contrarotating ring--ing bicoupled epicyciic gears, and an alternating-current

elec-ric motor. .A streamlined strut connects each pod rigidly to a

vertical steerable barrel which contains the i n d i v i d u a l l y -replaceable propuisor auxiliaries. Two power modules are re-movable and are mounted in the helicopter hangar. Each mod-ule comprises a 26,400 HP intercooled regenerated gas turbine, a 3 M w ship-service generator, and a propulsion generator with a second high-voltage winding for electrothermal guns.

I N T R O D U C T I O N T

I h e U.S. Navy recently requested the i d e n t i f i c a t i o n o f technologies which could lead to a capable, light, affordable (5,000 long ton, S500 million) destroyer for the 21st centu-ry. This saidy is a response to that initiative and is part of a continuing dedication to improving surface-ship and subma-rine perfotrnance and economy.

A senes of earlier papers [1,2,3] has shown a systems ap-proach which was intended to meet just such goals; the first major e f f o n which resulted was the Navy's Imegrated Elec-tric Drive Program which was initiated in the late 1980s. The current paper extends the systems approach into new concepts using the Navy's Advanced Surface Ship Evalua-tionTool (ASSET)[4] to show the effects of sequential intro-duction of vanous advanced propulsion subsystems on a de-stroyer

From the A S S E T data bank we obtain the Reference De-stroyer, a c o n v e n t i o n a l m e c h a n i c a l l y - d r i v e n gas-turbine ship with separate ship-ser/ice power generation, and assign it an armament suite. We then breaic down its weights and costs by Ship Work Breakdown Strucmre (SWES)"groups, and show which are the cost-cntical ones. A thermodynamic analysis of the propulsion process is then performed. This series of analyses indicates opportunities f o r improvement.

A sequence of f o u r e f f i c i e n c y - i m p r o v i n g changes is then

made to this open-shaft ship, each time creadng a new ship with the same length, sustained speed, endurance range, and stability, while allowing no excess volume and mamtaining a m i n i m u m freeboard. Weights and power losses are tracked at each step. The fifth ship incorporates a l l the m a j o r i m -provements typically assigned to open-shaft ships with inte-grated electric drive systems.

A C A P A B L E , A F F O R D A B L E 2 1 S T - C E N T U R Y D E S T R O Y E R

L E V E D A H L

The subsystems and components used in the fifth open-shaft ship are then introduced into a ship with a hull havmg a constant inward slope (mmblehome) to the topsides. The p r o p u l s i o n systems are modular and are i n d i v i d u a l l y re-placeable pierside for major maintenance. This new config-u r a t i o n has tconfig-urbine-generator m o d config-u l e s d e l i v e r e d to arid mounted i n the helicopter hangar and steerable-pod propui-sor units attached to the stern. F u r t h e r changes i n c l u d e adding an adjustable stem flap .and adding sufficient fuel to double the endurance range.

T H E O P E N - S H A F T R E F E R E N C E D E S T R O Y E R

The staning point is the Reference Destroyer which exists in the A S S E T data bank. It was assigned two 61cell V e r t i -cal L a u n c h Systems, a hangared helicopter with space for three spares, two 5 inch/54 calibre guns, and two Phalanx Close I n Weapons Systems ( C I W S ) . The machinery systems and h u l l are a l l p a r a m e t r i c a l l y described i n the A S S E T model. The first column o f Table 1 summarizes the Refer-ence Destroyer.

Figure-1 breaks down the 8174 ton weight and the S1.25

Table 1. Summary of the Destroyer.

R E F POD _{R A T I O D O U B L E R A T I O} D E S T D E S T T O R E F R A N G E T O R E F M a x i m u m speed, knots 31.46 31,73 1.009 31.70 1.008 Sustamed soeed 30.0 30,0 1.0 30.0 1.0 Endurance speed 20.0 20,0 1.0 20.0 1.0 Endurance range. N M i 6.000 6,000 1.0 12.000 2.0

McCreight Seakeeping Ind 13.9 17.8 1.28 16.7 1.20

Incipient cavitation vel 0 25.2 25.0 X

Number o f gas turbines 7 2 _{.286 .286}

Req d propulsion HP 81.682 45,622 .559 45.691 .559

Req'd Ship Service HP 6.935 3,894 .561 3.894 .561

Totai required HP 88.617 49,536 .559 49.585 .560

installed rated HP. 97.400 52,800 .542 52.800 .542

Total ship volume, ft^' 1.036.366 791.417 .764 791.417 .764 Total p l a t f o r m area, f t - 76.762 67.791 .883 67.791 .883 Lightship displacement L T 5146.1 4422.7 .859 4467.0 .868 M i l i t a r y payload 1189.8 1189.8 1.0 1189.8 1.0

Weapons load 401.5 401.5 1.0 401.5 1.0

Endurance Fuel 1724.] 701.9 .407 1481,0 .859

Full Load Displacement 8173.9 5614.8 .687 6438.1 .788 Structures W e i g h t (Gp 1) 2795.3 2079.5 .744 2079.5 .744 Girder (Gps 110-130) 1499.8 1276.2 .851 1276.2 .851 Propulsion System (Gp2) 763.4 366.3 .480 366.4 ,480 Shafting & D u c t i n g 364.0 69.5 .191 69.5 ,191 Electrical System (Gp3) 255.6 186.8 .731 186.8 .731 Au.xiliary Systems (Gp5) 775.9 575.0 .741 625.0 .806 Machinen,' Foundations 298.8 206.5 .691 206.5 .691 Machinery (2.3.5.Found) 2093.7 1334.9 .638 1384.9 .661 O u t f i t and Furnishings (Gp6) 508.4 429.9 .846 429.9 .846

Command and Surv (Gp4) 388.5 388.5 1.0 388.5 1.0

.Armament (Gp7) 399.8 399.8 1.0 399.8 1.0

Endur. ship-serve load M w 1.7141 1.582 .923 1.582 .923

Winter Battle SS load 3.1237 2.773 .870 2.773 .870

Volumetric coefficient ,00194 .00126 .649 .00134 .691 W L Length, f t 529 529.00 1.0 553 1.045 Length overall 555,6 560 1.008 579.6 1.043 M a x i m u m beam 55,65 55.04 .990 55.04 .990 Draft _{19,62 13.48 .687} 15.46 .788 Freeboard at station 7 24,0 24.52 1.022 22.98 .958

billion cost of the destroyer by Ship Work Breakdown Stmc-mre ( S W B S ) weight groups. The military payload includes the missile, ammunition and helicopter load; it also includes the C o m m a n d and Surveillance (Group 4) and A r m a m e n t (Group 7) parts of the ship. The military payload costs 63% of the total dollar cost. Only the 37% remainder is left f o r i m -provement by the marine engineer and naval architect.

O f this remainder, 7 0 % is the cost o f machinery, and only 12%, is-the cost o f structure. The propulsion system and electric power system together represent nearly half o f the non-payload cost, and consume all the f u e l . A n y serious cost-reduction effort must take these facts into account.

The propulsion and electrical systems perform two f u n c -tions. The first is to convert energy from one f o r m into an-other, starting with the chemical energy in fuel and air and ending w i t h thrust and electnc power. Engines, generators, -gears, motors, frequency conveners and propeUers f a l l i n

this category. The second category is transpon o f energy or fluids f r o m where they exist to where they are used.^This category includes electrical power distribution, turbine duct-ing, and propeller shafting.

In the reference ship the transport systems are nearly as heavy as their energy-conversion counterparts. Since trans-port-system sizes are direct f u n c t i o n s o f c o n f i g u r a t i o n , a major oppormnity is presented.

Power dissipation o f the propulsion system at m a x i m u m speed is illustrated in the R E F M A X column o f Figure 2. The m i n i m u m possible power which a hull o f this size can require is assumed to be the viscous effective power o f a T a y l o r Series (cruiser stem) bare h u l l . (Viscous power is calculated f r o m the f r i c t i o n c o e f f i c i e n t plus the portion o f the residuary resistance c o e f f i c i e n t derivable f r o m its value at Fr = 0.15, where wave resistance is negligible.) The rest o f the residuary resistance c o e f f i c i e n t is e'ssentially that f r o m waves and f r o m the stem shape which is intended to reduce wave resistance at high Froude numbers. The sum o f these additional residuary resistances are denoted here as "wave resistance."

A t m a x i m u m speed the .wave resistance o f this ship ex-ceeds the viscous resistance. The resistance o f propulsion appendages (including mdders) is about 45% o f the viscous h u l l resistance at all speeds. A miscellany o f loss c o m p o -nents is now added: skeg, b o w d o m e , and windage resis-tances and design margins. The latter include a m u l t i p l i e r o f 1.1 on power at all speeds; an additional multiplier o f 1.1 is applied at the 20-knot endurance speed. The next m a j o r loss is that due to propeller i n e f f i c i e n c y ; the propulsive c o e f f i -cient is about .68. The 2.5% transmission inefficiency and the ship service power production are now added. The total turbine power requned is over 3.8 times the basic viscous effective power at m a x i m u m speed, and over 3.4 times at the sustained speed o f 30 knots.

The f u e l tank is sized at the 20-knot endurance speed. Wave drag is small, but the submerged transom resistance is non-negligible. The propulsion appendages retain their 4 5 % of hull viscous resistance. Propeller and transmission e f f i -ciencies and ship-service requirements total about the same, fractionally, as at m a x i m u m speed; the overall m u l t i p l i e r on ideal viscous loss is about 2.5 at cruise speed.

Figure 3 shows the losses, including turbine losses, at the

L E V E D A H L

A C A P A B L E , A F F O R D A B L E 2 1 S T - C E N T U R Y D E S T R O Y E R

100% —

WEIGHT, PERCENT OF TOTAL COST, PERCENT QF TOTAL

Figure 1. Weigtit and cost distributions of the Reference Ship.

20 knot endurance speed where fuel consumpdon is calcu-lated. The energy contained in the fuel burned is ten times the viscous effecdve power, which implies an overall e f f i -ciency of 10%! Turbine ineffi-ciency is thus a major oppor-tunity for improvement, since the propulsion turbines were only 25% efficient and the shipservice turbines 15 % e f f i -cient at this speed. A t higher ship speeds, in spite o f the fact that the e f f i c i e n c y o f a simple-cycle turbine improves as load increases, the net efficiency is yet lower than 10% be-cause o f increased wave resistance.

T o summarize the reference ship and its power systems: wave resistance, propulsion appendages, propellers and tur-bines are obvious opportune targets for e f f i c i e n c y improve-ment; nonproductive transpon weights abound.

M O D I F I C A T I O N S OF T H E O P E N - S H A F T R E F E R E N C E D E S T R O Y E R

We now present the first five o f a sequence o f ten ships w h i c h shows the effects on weight and e f f i c i e n c y o f each change. Figure 4 shows the changes in power and number o f turbines, weights o f machinery and fuel, and l i g h t s h i p / f u i l -load displacement respectively. Figure 2 shows the

distnbu-tion o f hydrodynamic and transmission losses at maximum, speed. Figures 3 is a corresponding plot at the endurance speed o f 20 knots w h i c h includes turbine i n e f f i c i e n c i e s . Supporting data are presented in Table 2.

REFERENCE D E S T R O Y E R

-The Reference Destroyer ( R E F M A X ) is a conventional, m e c h a n i c a l l y - d r i v e n o p e n - s h a f t d e s t r o y e r w i t h f o u r L M 2 5 0 0 propulsion engines geared to two controllable-re-versible-pitch propellers and w i t h three 5 0 I K 17 engines geared to three two-pole 60 Hz alternators.

P R O P U L S I O N - D E R I V E D S H I P S E R V I C E P O W E R

Propulsion-Derived Ship Service Power (PDSS) is intro-duced [ 5 ] . T w o o f the 2-pole ship service alternators are re-placed by multipele alternators connected to propulsion tur-bines or to the high-speed side of the reduction gear Since f u l l power must be produced by the alternator even when engine speed drops by two thirds, these alternators must have three times the capacity of those they replace. Cyclo-converters were added since high-quality 60 Hz power must

A C A P A B L E , A F F O R D A B L E 2 1 S T - C E N T U R Y D E S T R O Y E R L E V E D A H L f.; üi S 5 0 , 0 0 0 O Q. UJ g 4 0 , 0 0 0 -z 3 0 , 0 0 0 2 0 , 0 0 0 A 1 0 , 0 0 0 m S H I P - S E R V I C E P O W E R • T R A N S M I S S I O N M P R O P E L L E R • B O W D O M E . S K E G S , W I N D A G E M A R G I N S • P R O P U L S I O N A P P E N D A G E S • W A V E • V I S C O U S H U L L 4 J

i M i i m i

Figure 2. Loss distribution of 10 ships, at maximum power.

be produced regardless o f alternator speed. The combined efficiency o f the -altemator-cycloconverter is . 8 0 instead o f the . 9 5 o f the standard alternator The advantage o f this new, less e f f i c i e n t and heavier combination is that""'! is powered by an already operating gas turbine w i t h an incremental spe-c i f i spe-c f u e l spe-consumption about 1/3 o f the overall spespe-cifispe-c f u e l consumption o f the 5 0 I K turbines. The net result is a 6 0 % reducdon i n ship-service f u e l consumption. The overall con-sequence is the eliminadon o f two 5 0 I K engines, a 1 2 % re-ducdon i n endurance f u e l and 4 % reductions i n required power and machinery weight.

I N T E R C O O L E D R E C U P E R A T E D G A S T U R B I N E S

Intercooled Recuperated Gas T u r b i n e s [ 6 ] ( I C R ) d i r e c t l y replace the simple-cycle L M 2 5 0 0 turbines in the preceding ship, w h i c h has p r o p u l s i o n - d e r i v e d ship service. The en-gines are heavier, thanks to heat exchangers, but a i r f l o w is smaller, leading to reduced ducting. Com^pared to the previ-ous step there is a 2 8 % reduction in fuel consumption and 4% reduction in required power, accompanied by a small in-crease in machinery and lightship weights.

D I R E C T D R I V E , S O L I D - S T A T E - C O N T R O L L E D , A C E L E C T R I C M O T O R

A D i r e c t D r i v e , S o l i d - S t a t e - C o n t r o l l e d , A C E l e c t r i c M o t o r ( D I R E L ) replaces each locked-train double reduction gear. Since the motor can be reversed, fixed pitch propellers With smiall shafting and struts replace heavier controllable r e v e r s i b l e p i t c h propellers and their larger s h a f t i n g and struts. Since electrical cross connection between the t w o shafts is now possible, three uprated propulsion engines and alternators replace the f o u r propulsion engines o f the previ-ous case. A 28-ton battery energy storage system permits operation on one turbine f o r cruise, while"providing interim ship service power between failure o f the operating turboal-temator and starmp o f a replacement. A 15% reduction i n f u e l c o n s u m p t i o n is accompanied by a 2% r e d u c t i o n i n power. M a c h i n e r y weight increases because o f the large s p e c i f i c w e i g h t o f electric machines w i t h l o w r o t o r t i p speeds.

G E A R E D E L E C T R I C D R I V E

Geared Electric Drive ( G R E L E C ) involves the replace-ment o f the large-diameter low-speed motor w i t h a small-di-ameter high-speed motor and a ring-ring bicoupled contraro-tating e p i c y c i i c gear, Contrarocontraro-tating propellers, s h a f t i n g , and thrust bearings replace the fixed-pitch propellers and shafting. The reduction in f u e l is sizeable, and is primarily

L E V E D A H L A C A P A B L E , A F F O R D A B L E 2 1 S T - C E N T U R Y D E S T R O Y E R 1 0 0 , 0 0 0 9 0 , 0 0 0 ^ ^ S H I P - S E R V I C E T U R B I N E S ü M A I N T U R B I N E S M S H I P - S E R V I C E P O W E R • T R A N S M I S S I O N • P R O P E L L E R • B O W D O M E , S K E G , W I N D A G E , M A R G I N S • P R O P U L S I O N A P P E N D A G E S • W A V E H . V I S C O U S H U L L 10,000 C O N F I G U R A T I O N

Figure 3. Loss distribution of 9 ships, including turbines, at 20 knots.

due to the e f f i c i e n c y of contrarotating propellers, panly due to improved motor efficiency, and mitigated by slightly-in-creased s h a f t i n g resistance. T h i s is the f i r s t instance o f m a j o r synergistic benefit, w i t h reductions o f 15% i n re-quired power, 10% i n fuel consumption, 9% i n machinery weight, and 6% i n both lightship and f u l l - l o a d displacement..

The overall improvement over the Reference Destroyer i n this, our final open-shaft ship, include an impressive 5 2 % reduction in f u e l consumption, but only 5% i n machinery weight and 4 % i n lightship weight. These unbalanced i m -provements provide a 14% reduction in fuU-load displace-ment and a 25% reduction in required-power. The latter fig-ure j u s t i f i e s the. r e d u c t i o n i n . the. n u m b e r o f p r o p u l s i o n nirbines f r o m f o u r to three. The resultant benefits seem to be solely the result of higher-efficiency components and. the.increase in system e f f i c i e n c y of having only one. turbine, i n -stead o f f o u r , operational aL the. c o n d i t i o n f o r w h i c h f u e l consumption is calculated.

Is this final open-shaft ship a welLintegrated,_synergized. highly leveraged ship which should be h i g h l y affordable? The answer is no. W h i l e we could introduce endless variants on the vanous machinery types involved here, and pick up a percent here and there, the overall picmre does not change-substantially until we take a different approach. Funher, the

changes we have m.ade here make only modest concessions to f u t u r e requirements f o r greater stealth, less p o l l u t i o n , lower manning, easier maintenance, and greater simplicity.

Since we have reached a dead end i n the sequence o f changes to the conventional ship, we now digress i n order to describe the characteristics o f an i m p r o v e d ship concept which w i l l embody the second five o f the ten-ship series. The next two sections are devoted to this description and the rationale behind it.

T W E N T Y - F I R S T C E N T U R Y D E S T R O Y E R G O A L S A N D D E S I G N S E L E C T I O N

A t w e n t y - f i r s t cenmry ship requires several s i g n i f i c a n t i m p r o v e m e n t s w h i c h are n o r available: w i t h o u t a. m a j o r change i n philosophy and configurations. W e - m u s t d e p a r t s i g n i f i c a n ü y f r o m the reference hull,, w h i c k incorporated the m a j o r e f f e c t i v e systems improvements- available to open-shaft ships.-We imposed on-ourselves the following-design goals. ..

-1. A l l machinery subsystems must be prealigned, pretested, and pierside installable and replaceable.

2. Each ship enclave (comparmient) must be self sufficient

A C A P A B L E , A F F O R D A B L E 2 1 S T - C E N T U R Y D E S T R O Y E R L E V E D A H L 9000 8000 — UJ tX o LU f— u. m LLf LU c e Q z O 5-(/) X 1 ( / ) LU U_ t r 5 LU Q . cr: CO < S i O i r t -u UJ UJ -i > UJ Q 1,1 i cc O O 5 5 i s I È w LU LU Q - 1 I - O CQ CO a. : o • UJ C5 1 -( 0 m CO b 5 UJ ce < Q . O I Ü - R E Q U I R E D P O W E R HP/10 - M A C H I N E R Y W E I G H T LT - L I G H T S H I P D I S P L A C E M E N T LT • FUEL W E I G H T LT • FULL L O A D D I S P L A C E M E N T LT N U M B E R O F TURBINES/1000 1 < O l 1 CE ' UJ < 1 O ce UJ O CN RE D _ 1 O CN RE D PROPE L B Y o z < cc OJ -J to D O Q

Figure 4. Required power, number of turbines, and weights of 10 ships.

under emergency conditions except for elecuic power. 3. The ship should be stealthy. Propellers must not cavitate

below 25 knots. The radar cross section seen by other ships and by sea-skimming missiles must be very low. Its infrared signature must be small at any angle above the bonzon.

4. It must have the potential of global range, unaccompa-nied, and then be able to perform its mission. (12,000+ nautical miles)

5 . We must provide the capability to upgrade either the 5-inch guns, the Close In Weapons System ( C I W ^ ) , or both to hypervelocity elecu-o-chemical-thermal guns [7] using the propulsion turbines and/or the kinetic energy of the hull for power.

6. We must uy to reach a low hull, machinery and electrical . (HM&E) cost, aiming for half that of the Reference

De-stroyer.

7. In accord with future international pollution-conu-ol lim-its, no fuel tank may be ballasted by dischargeable water. 8. The ship structure must be resistant to destruction by

mine explosions.

We designed a two-engine box-girder ship w i t h 10 degree cumblehome w i t h the h u l l and steel super structure struc-turally integrated. A f t e r completion o f the h u l l , two dock-side-removable external propuisor modules are attached to the stem and two turbine-generator modules are installed in the helicopter hangar. Several concepts are evaluated usina this basic h u l l shape.

A box-girder ship is reladvely tolerant o f shallow-water

mine explosions. T w o box girders, whose upper surfaces de-fine the weather deck before and abaft the integral super-structure, run the length of the ship: each has a normal 9 foot deckheight and is wide enough to contain all longitudi-nal electnc and f l u i d lines and provide a walkway. The box girders are connected to the companments only via electri-cal plugs and via f l u i d lines w i t h appropriate shutoff valves inside and outside the box.

The hull girder has these two boxes and the keel as its p n -mary members. The shell p l a r i n g , the inner b o t t o m and sides, and the superstructure, w h i c h is a continuation o f the box girder, are all strength members. Figure 5 shows the compartment configurations and the outer hull. H i g h - y i e l d steel could be used in the super sonjcmre smce its top is far-ther f r o m the neutral axis than any ofar-ther part o f the ship. Holes m the super stmcture sides f o r turbine exhausts, f o r

Figure 5. Hull and compartmentation. I S N a v a l E n g i n e e r s J o u r n a l . M a y 1993

L E V E D A H L

A C A P A B L E . A F F O R D A B L E 2 1 S T - C E N T U R Y D E S T R O Y E R

Table 2. Characteristics of the 10 Ships with H M & E Losses.

1 1 1 1 T A B L E 2 ! 1 C H A R A C T E R J S n C S | R E r O £ S 1 P t J S S I C R 1 D I R E L G R E L E C P O O N O S S T G 1 E A R . S F L A P 12 X R A N G E R E Q U I R E D H O R S E P O W E R | S S , S 1 7 _{1 5 3 , 1 8 6 7 9 , 5 6 6 1 7 8 , 1 4 2 5 5 , 3 4 3} 5 1 , 1 6 0 5 1 , 1 2 0 1 4 3 , 5 3 6 4 4 , 7 5 8 1 4 9 , 4 5 0 N U M B E R O F T U R B I N E S | 7 5 5 1 4 4 1 3 2 1 2 2 1 2 M A C H I N E R Y W E I G H T , L T O N S j 1 , 7 9 5 1 . 7 5 1 1 1 , 8 1 7 1 1 , 8 7 2 1 , 7 0 4 1 , 2 0 3 1 , 1 4 0 1 1 , 1 2 8 1 . 1 7 5 1 1 , 1 7 5 U S A B L E F U E L W E I G H T | 1 , 7 3 . 4 1 , 5 1 9 1 1 , 0 S S i 9 2 2 8 2 8 7 2 8 7 1 6 1 7 0 2 7 0 1 1 1 . 4 3 1 M I U T A R Y P A Y L O A D W E I G H T | 1, 1 9 0 1 , 1 9 0 1 1 , 1 9 0 1 1 , 1 9 0 1 , 1 9 0 1 , 1 9 0 1 , 1 9 0 1 1 . 1 9 0 1 , 1 9 0 ₁ 1 , 1 3 0 U G H T S H I P D I S P L A C E M E N T | 5, 5 3 7 5, 5 0 1 5 , 5 3 3 1 5 , 0 4 5 5 , 6 7 9 4 , 5 8 3 4 , 4 3 7 1 4 , 4 2 2 1 4 , 4 6 7 4 , 5 0 3 F U L L - L O A D D I S P L A C E M E N T I 8 , 1 7 4 7 , 5 6 2 7 . 5 0 7 1 7 , 4 6 7 7 , 0 0 6 1 5 , 8 0 9 5 , 5 4 ^ 1 5 , 5 1 5 1 5 , 6 5 8 5, 4 7 4 L O S S E S , M A X S P E E D , H P 1 V I S C O U S H U L L 1 8 , 7 7 2 1 8, 5 5 9 1 3 , 5 5 2 1 3 , 7 5 3 1 8, 5 4 9 1 7 , 6 9 5 1 7 , 5 2 5 1 7 , 4 5 9 1 8 , 0 7 0 1 3 , 0 5 4 • W A V E 1 1 9 , 5 9 5 1 8 , 1 4 7 1 6 , 5 3 0 1 1 6 , 2 9 2 1 4 , 5 4 5 8 , 8 9 2 3 , 4 5 4 3 , 3 6 4 1 5 , 5 3 2 5 , 6 4 3 P R O P U L S I O N A P P E N D A G E S I 9 , 2 4 5 8 , 8 9 7 3 , 5 1 9 1 5 , 3 4 0 5, 9 8 7 1 3 , 5 0 9 3, 5 0 7 3 , 4 3 5 1 3 , 4 3 5 3 , 4 8 6 B O W D O M E . S K W I N O . M A R G | 6 , 2 3 4 S 0 6 5 5 9 7 5 1 5 6 1 8 5 3 2 2 1 4 3 3 9 4 2 5 3 4 2 4 5 1 4 2 0 9 4 , 3 8 5 P R O P E L L E R 1 2 5 , 5 5 0 2 4 S 9 1 2 3 4 4 2 1 2 1 3 3 3 1 2 9 1 5 1 0 3 4 9 1 0 0 8 3 5 8 0 8 1 8 2 5 5 8 , 8 0 7 T R A N S M I S S 1 2, 0 2 5 1 3 4 0 1 8 5 3 1 5 1 5 4 4 6 0 2 3 4 5 8 3 3 9 2 3 2 8 0 1 3 2 8 0 3 , 2 8 0 S H I P - S E R V P O W E R | 4 , 5 2 3 4 7 8 0 4 7 3 0 1 4 6 0 2 4 4 1 8 4 3 6 2 3 9 0 5 3 3 3 4 1 3 8 3 4 3 , 8 9 4 M A I N T U R B I N E S j 1 7 7 ,4 S S 1 7 1 , 2 9 7 1 1 1 , 3 9 2 1 1 0 9 , 9 7 8 5 3 , 7 7 2 7 3 , 6 5 0 7 1 , 5 6 8 5 9 3 5 0 1 6 4 , 9 8 0 5 3, 3 4 0 S H I P - S E R V T U R B I N E S | 1 6 , 8 1 4 1 1 _{1 1} L O S S E S , 3 0 K N O T S , H P | ₁ 1 1 E F F E C r r V E P O W E R | R E F 3 0 P O S S 1 I C R D I R E L G R E L E C P O D N O S S T G1 E A R . S 1 F L A P 1 Z X R A N G E V I S C O U S H U L L j 1 6 , 3 4 6 1 5 , 1 3 3 1 6 , 0 1 2 1 5 , 2 2 1 1 5 , 8 1 6 1 4 , 9 9 1 1 4 , 5 4 7 1 1 4, 5 2 2 1 1 5 . 3 4 1 1 1 6 1 4 3 W A V E 1 1 3 , 6 2 4 1 2 5 8 1 1 1 4 1 9 1 1 2 1 1 3 8 3 7 5 5 8 8 5 3 4 7 1 5 2 9 7 1 2 8 7 5 3 , 5 0 6 P R O P U L S I O N A P P E N D A G E S I 8 , 0 4 3 7 7 3 3 7 5 9 9 , £ 0 7 3 5 1 8 8 3 0 4 0 3 0 2 9 1 3 0 1 8 1 3 0 1 8 3 0 1 3 B O W D O M E . S K W I N D . M A R G | 5, 1 1 8 4 9 6 3 4 6 2 3 4 5 7 4 4 2 7 8 3 5 1 5 3 4 5 9 J_ 3 4 5 6 | 3 4 2 7 \ 3 , 5 1 5 P R O P E L L E R 1 2 0 , 4 4 7 1 9 5 5 1 1 5 5 9 5 1 7 2 9 1 1 0 3 4 5 8 3 2 2 3 1 0 8 1 7 0 3 9 1 6 5 2 8 1 5 . 3 4 4 T R A N S M I S S j 1 , 7 5 3 1 5 3 8 1 6 2 0 4 4 6 2 4 0 3 0 3 0 4 5 2 9 8 2 1 2 8 8 2 2 6 7 3 1 2 , 8 4 7 S H I P - S E R V P O W E R j 4 . 5 2 3 4 7 5 6 4 7 0 6 4 S 0 S 4 4 2 4 4 3 6 2 3 9 0 6 1 3 8 9 2 3 3 3 2 1 3 8 9 2 M A I N T U R B I N E S | 1 5 7, 0 4 1 1 4 9 , 4 5 5 9 0 , 4 0 6 8 3 , 2 5 6 7 5 , 9 5 5 5 0 , 1 5 0 5 3, 3 4 9 1 5 5 , 5 5 8 1 5 3 . 1 3 4 1 5 6. 2 4 6 S H I P - S E R V T U R B I N E S I 1 6 , 8 1 4 | 1 1 1 1 j _{1 1 1} L O S S E S , 2 0 K N O T S , H P 1 1 ₁ E F F E C T I V E P O W E R | R E F 2 0 | P D S S I C R 1 D I R E L 1 G R E L E C P O O 1 N O S S T G 1 E A R . S j F L A P 2 X R A N G E V I S C O U S H U L L 1 5, 0 2 2 | 4 9 7 4 1 4 9 7 4 1 4 9 5 3 1 4 8 5 3 4 6 0 5 1 4 5 6 1 1 4 5 5 3 1 4 5 5 3 5 , 2 7 9 W A V E 1 3 2 2 1 8 1 1 \ 6 3 6 1 S 2 9 i 5 2 0 3 7 4 1 2 5 5 1 2 2 5 1 2 2 S 3 4 0 P R O P U L S I O N A P P E N O A GcS ! 2 , 5 3 1 ! 2 S S S | 2 7 4 2 1 1 5 7 4 | 1 7 2 6 1 1 6 0 1 1 1 5 3 1 1 1 5 2 1 1 1 5 2 1 , 1 5 2 3 0 W [ X ) M E , S K W 1 N 0 , M A R G 1 3 , 1 9 9 | 3 1 4 5 | 3 0 3 4 1 2 9 4 0 1 2 5 4 9 1 2 5 4 1 1 2 5 0 6 1 2 5 9 3 | 2 5 9 3 | 2 , 7 4 9 P R O P E L L E R i 5, 4 3 6 I 5 3 5 7 | 5 1 9 6 1 4 7 6 0 1 3 0 3 2 1 2 5 3 2 1 2 6 1 8 1 2 2 6 4 1 2 2 S 4 1 2 , 5 0 4 T R A N S M I S S 1 6 9 6 1 5 7 5 ( 5 5 3 j 1 7 1 0 j 1 7 0 2 1 1 4 5 3 1 1 4 2 6 1 1 3 7 2 1 1 3 7 2 I 1 , 4 7 4 S H I P - S E R V P O W E R | 2 , 5 2 2 | 2 5 4 2 | 2 6 1 5 ! 2 5 3 2 | 2 5 3 0 1 2 2 7 8 1 2 2 2 8 1 2 2 2 2 | 2 2 2 2 | 2 , 2 2 2 M A I N T U R B I N E S j 5 3 , 6 1 4 | 5 6 5 3 2 3 5, 5 0 a 1 2 7 3 4 6 | 2 4 , 7 4 3 1 2 1 , 5 2 9 1 2 1 , 4 6 2 1 2 1 , 2 0 0 I 2 1 , 2 0 0 I 2 1 , 9 5 4 S H I P - S E R V T U R B I N E S i 1 4 , 2 9 5 | _{1 f 1 1 1 1}

launching ship's boats and in the rear for the helicopter-hangar door w i l l be reinforced.

Weapons systems, c o n s i s t i n g o f two 6 1 - c e l l v e r t i c a l launch systems, two 5-inch 54 calibre guns, and two Pha-lanx close-in weapons systems are mounted after comple-Uon o f the hull stmcture.

T w o separate propuisor units and two power modules are also mounted after completion of the hull structure and are shown in Figure 6. Figure 7 shows the assembled ship in top and side views. Figure 8 is a rear view o f the propulsion sys-tem and Figure 9 is a view, shown with the addition o f a re-tractable stem flap.

The f o l l o w i n g teamed ideas and technologies are synthe-sized into this concept.

1. Contrarotating tractor propellers, facing directly into the undisturbed flow stream outside the hull boundary layer, provide high efficiency and no cavitation at speeds up to 25 knots except in sharp tums and rapid accelerations. 2. Compact electric ac propulsion motors, contrarotating

nng-nng bicoupled gears, thrust bearings, and seals com-bine into a single rigid pretested propuisor capsule which drives the contrarotating propellers.

3. The propuisor capsule is slid into a streamlined cylindrical pod, with one acoustically-compliant mounting point for-ward and one aft.

4. A streamlined strut connects each pod rigidly to a steer-able barrel-shaped auxiliary machinery room. Manned entry into the rear of the pod from the machinery room is

A C A P A B L E . . A F F O R D A B L E 2 1 S T - C E N T U R Y D E S T R O Y E R _{L E V E D A H L}

CIRCULATIO.K CONTROL PORT

MOTOR

Figure 6. Propuisor capsule, propuisor units, power modules.

through the after part of the strut. Access forward is via the forward extension of the strut.

5 . Steering during major maneuvers is done using a high-ratio orbital drive which is integral with the moderately-loaded, large-diameter roller bearing which supports the

entire rotatable pod and barrel system and transmits thrust to the structure. Normal steering corrections are quietly made by preferential ejection of cooling water through the port or starboard after sides of the struts, providing circula-tion control via the Coanda effect. Fast crashback is

L E V E D A H L

A C A P A B L E , A F F O R D A B L E 2 1 S T - C E N T U R Y D E S T R O Y E R

Figure 8. Propulsion system, aft view.

actiieved by rotating the pods in opposite directions. 6. The barrel contains individually-replaceable auxiliary

ma-chinery which supports the propuisor system, and is steered by orbitally-geared electric motors.

7. Each steerable pod drive and its auxiliary systems are combined into a detachable, pretested, shore-maintainable unit which can be removed and replaced pierside with a crane. There are two of these units per ship, and both at-tach to the stem. The units form naturally-shaped exten-sions to the hull. The upper part of each unit is available to deploy towed arrays. Provision is made to extend a re-tractable flap from the bottom of the unit.

8. A tumblehome hull, with all topside areas at the same in-ward angle to the venical, and with no right angles at any surface intersections, decreases radar detectability from ships or from surface-skim.m.ing m.issiles by several orders of magnitude from its vertical-sided predecessors. A clean outer surface enhances the low radar cross section; most deck machinery, bins, bollards, cleats, etc„ wiil be hidden from view, and stanchions, lifelines, etc. will be carefully designed, possibly retractable. Antennas wiil be contained within weapons when possible, conformal in most other cases, with the intent of minimizing or eliminating the

need for masts.

9. In the next century it is probable that ecological reasons will preclude admitting seawater to a fuel tank for ballast-ing and dischargballast-ing it for refuelballast-ing. .An advantage of die tumblehome configuradon is that when fuel is added the wateriine beam decreases and the righdng moment and roll period tend to stay constant. The need to ballast to com-pensate for burned fuel is reduced or eliminated. By con-trast, the venical-sided hull of the Reference Destroyer re-quires seawater ballasdng; destroyers with tiared hulls require yet more.

10. This tumblehome configuration also permits mounting of the engines above the girder, exhausting downward, with-out the ducting extending beyond the wateriine beam of the ship or occupying ship volume aloft. A shon-duct, boundary layer infrared shielded air-induction-cooled ex-haust system, aiming downward and abeam, minimizes in-frared detectability from any point above the honzon. I f the side exhaust is temporarily swamped by a rogue wave, the exhaust gases will escape via the infrared sliields. A short venical uptake is an alternative which would have higher infrared visibility from above but would permit op-eration of the engine pierside or in a nested configuration. 11. The turbine, the ship service alternator, and the propulsion

alternator (with an optional second high-voltage winding for advanced electric guns) are built into a module which can be loaded at dockside onto the helicopter deck and into the hangar for installation or replacement.

12. The hull is segregated longitudinally mto ecologically self-sufficient compartments. Survivable box girders carry all electrical and fluid lines; no longitudinal air, gas, or liquid lines penetrate the companments except fire mains with a shutoff valve on each side of the bulkhead.

13. A vanable-angle, retractable dap attached to each propui-sor module can be deployed to increase waterline length and to permit optimum trim of the ship; this results in a significant reduction in power required under many condi-dons. .A significantly increased fuel load can be canied without increased maximum engine power.

The f o l l o w i n g ideas already incorporated into the open-shaft concept are retained:

14. ,An intercooled, recuperated gas turbine is included be-cause it greatly increases efficiency, reduces auflow, and funher reduces exhaust gas temperature and infrared de-tectability. Its addihonal weight is far more than

compen-Figure 9. Ship with retractable stern flap.

A C A P A B L E . A F F O R D A B L E 2 1 S T - C E N T U R Y D E S T R O Y E R _{L E V E D A H L}

sated by fuel savings.

! y One engine can provide f u l l ship-service power and

propulsion power at speeds up to at least 25 knots. A ship-service alternator and a propulsion alternator are mounted on each turbine shaft. Ship sen/ice power at anchor is pro-vided by the ICR engine far more efficiently than by cur-rent ship-service turbogenerator sets and widiout their ad-ditional weight and expense.

16. A battery energy storage system powers vital loads during the short time between the potential failure of a single op-erating engine and the starmp and bringing on-line of the other engine.

Table 1 presents the 6,000-Mi-range Reference Destroyer, the comparable podded ship without flap, and the podded 5hip w i t h flap and w i t h f u e l to provide a 12,000 mile en-iurance range, showing ratios o f each value to that o f the Reference Destroyer. Table 2 provides summary data for all 10 ships.

M O D I F I C A T I O N S O F T H E P O D D E D D E S T R O Y E R We now discuss the last f i v e members of the ten-ship se-luence. Figure 4 shows the changes in power and number of urbmes. weights o f payload. machinery and f u e l , and light-n i p / f u l l - l o a d displacemelight-nt. Figures 2 alight-nd 3 show the distlight-n- distnbution o f hydrodynamic and transmission losses at m a x i -num speed and 20 knots respectively.

' O D D E D PROPELLER

The step to the podded ship (POD), retaining all the pre-•lous machinery except one I C R turbine and its propulsion

itemator. is enormously synergistic. The number o f tur-nnes decreased 2 5 % , r e q u i r e d p o w e r 2 3 % , m a c h i n e r y veight 29%, fuel weight 12%, lightship 19%, and f u l l load

isplacement 17%. D u c t i n g and s h a f t i n g w e i g h t is o n l y 9 . 1 % o f the reference-ship values.

x i M i N A T i N G G A S T U R B I N E ( N O S S T G )

The remaining 50 I K ship service turbine performs no re-uired function; eliminating it reduces the total number of irbines to two and reduces machinery weight 5%. A l l other 'eights are also reduced sympathetically.

.EDUCED B L A D E A R E A R A T I O ( E A R . S )

The propeller blade area ratio was 1.0, providing an incip-:nt cavitation speed of 28.6 knots, compared to the Refer-nce Destroyer w h i c h cavitated at all speeds. Reducing the lade area ratio to 0.8 reduces c a v i t a t i o n speed to 25.2 nots. while decreasing required power 3%, and fuel con-i m p t con-i o n 2%.

E T R A C T A B L E F L A P ( F L A P )

Deploying a retractable flap o f 24 foot length, equal to the ;ighf o f the transom, has a major effect on the resistance at

gh speed because o f the decreased Froude number and j i u m e t r i c c o e f f i c i e n t , and the opportunity to provide the

most e f f e c t i v e transom submergence at all speeds. A t en-durance speed the f l a p may be retracted to reduce wetted surface. T h e separately-calculated reduction i n required m a x i m u m power is 9%. The flap and mechanisms were esti-mated to weigh 50 tons.

D O U B L I N G R A N G E ( 2 x R A N G E )

The flapped ship has excess power capability and a very small f u e l load. A d d i n g another 787 tons o f fuel doubles the range to 12,000 miles and requires about the same horse-power as the 6,000-mile unflapped ship.

D I S C U S S I O N OF R E S U L T S

It is instmctive to examine each chart f r o m the reference ship through to the last ship; a few basic observations may help a curious reader in his quest to understand what is and what is not important.

The first o f these observations is that doing the right things to the hull, mechanical, and elecnical system ( H M & E ) can make a major difference i n perfonnance and cost. This find-ing opposes a pandemic feelfind-ing that many i n the Navy seem to have. They don't believe that anything done to surface ship H M & E components can be important. The potential ad-vantages of this ship over the reference ship include greater simplicity, longer range, greater stealth, greater maneuver-ability, better seakeeping, more prime real estate (at the cen-ter o f the ship) devoted to officers and men, lower manning requirements, fewer auxiliary ships required for refueling, re-duced pollution, and lower cost. " L o w e r cost" is the phrase in vogue as this is written, but may i n time revert to "better value."

W e have chosen not to present incremental cost projec-tions f o r the concepts shown here, because appropriate com-putational tools are not available to us. However, two tur-bines are cheaper to buy, maintain, and feed than are seven. A l s o , i t is apparently agreed that most machinery, most stmcture, and most f u e l have costs w h i c h are approximately proportional to their weights. I t also seems agreed that pre-assembled, prealigned and pretested machinery saves the enormous cost of aligning machinery i n the ship. Propeller shafting is a fine example o f this thesis.

A second o b s e r v a t i o n is that it is o f t e n i m p o r t a n t to change more than one thing at a time, and to have these changes benefit the ship i n more than one way. Synergism,

leverage, serendipity, and lucl< seem to w o r k together to

help the very-rare good m u l t i f a c e t e d change. These f o u r goddesses o f the systems engineer are very selective. W e have reported here only b e n e f i c i a l changes; thorough re-portage o f all the others that have been investigated would make a disastrously long encyclopedia. Even here, only two of the increments presented were truly synergistic i n that ev-erything improved at once. These were the change to geared electric drive with contrarotating propellers, and the change to the podded tumblehome configuration.

A t h i r d o b s e r v a t i o n is that p r o p e r l y selected m a j o r changes i n configuration can simultaneously improve e f f i -ciency, signatures, simplicity, weight, and cost. T w o major examples were the removal o f m a j o r machinery f r o m the

L E V E D A H L

A C A P A B L E , A F F O R D A B L E 2 I S T - C E N T U R Y D E S T R O Y E R

hull, and making the deckhouse a continuation o f the bo.x girder. The consequent short shafts and shon ducnng reduce weight, pod resistance is much lower than open shafting and rudders, and acoustic, radar, and infrared signanires almost automatically improve.

A fourth observadon is that further improvements require tradeoffs; increased range requires more power or the use o f a flap, f o r instance. It is the further, and frequently minor, changes that trade o f f one against another. These tradeoffs, however, never provide earth shaking improvements.

A f i f t h o b s e r v a t i o n is that many p o t e n t i a l l y v a l u a b l e changes in subsystems, particularly in auxiliary machinery, should also be evaluated. We estimate that an improved auxil-iary-machinery suite might increase the potendal range o f the podded and flapped ship by as much as 3.000 N M i . Describ-ing these systems in sufficient detail for inclusion in ASSET could permit an accurate evaluation of the benefits, and assist in convincing the world o f the value of improving these sys-tems.

A sixth observadon is that A S S E T is a viable technology-evaluarion tool which assesses the ship impacts o f machm-er\'-subsystem opdons in a controlled and repeatable fash-ion. W i t h A S S E T , the philosophy o f c o m p a n n g ships o f

equal capability was enforced. A l l propulsion and

electricplant subsystems studied here, i n c l u d i n g pods and p r o -pellers, e.xisted as built-in documented options. A d d i d o n a l capability to assess vanous concepts should be incorporated into ASSET as these technologies progress. A S S E T has the f l e x i b i l i t y to model unique configurations, such as the tum-blehome hull and deckhouse.

C O N C L U S I O N S

Reduction o f required power, rather than reduction o f structural weight, is essential to making ships more a f f o r d -able.

Properly c o n f i g u n n g the hull, mechanical, and electrical system can greatly s i m p l i f y a ship, providing that several changes are made at the same time. The changes w h i c h sim-p l i f y the sim-prosim-pulsion and electrical systems greatly reduce the power and fuel required, and almost automatically

pro-vide greater stealth, greater maneuverability, better seakeep-ing, better maintainability, lower pollution, and many other benefits which should result i n lower cost.

We have only scratched the surt'ace in showing h o w to make ships simpler and better by reconfigunng the propul-sion machinery. The yet heavier electnc and a"uxiliary sys-tems are far less well integrated into most ships, and respon-s i b i l i t y f o r their d e respon-s i g n and respon-s e l e c t i o n irespon-s m o r e d i f f u respon-s e . Improvement in their configuradons is clearly a major op-portunity.

A wide range of opponunities lies in the selecdon o f sim-pler and more efficient subsystems than those used in this study. Subsystem and component improvement are a fertile source o f potential s i m p l i f i c a t i o n , efficiency increase, and (by implication) cost reduction.

These benefits were established using ASSET, the N a v v ' s technology evaluation tool. Extension o f its use to evaluate other subsystems, particularly auxiliary-machinery systems, w o u l d show the potendal o f these altemadves.

REFERENCES

[1] "Superconductive Naval Propulsion Systems." William J. Levedahl, Applied Superconductivity Conference, 1972. [2] Tniegrated Machinery Systems which Result in Small, E f f i

-cient Destroyers," William J. Levedahl. Naval Engineers

Journal. .Apnl. 1980.

[3] "Integrated Ship Machinery Systems Revisited." William J. Levedahl, Naval Engineers Journal. May, 1989

[4] .ASSET, Advanced Surface Ship Evaluation Tool, DTRC Contract N00167-85-D-0017, User Manuals Vols 1-2E, Boe-ing Computer Services Company.

[5] "Application of Vanable Speed Constant Frequencv Genera-tors to Propulsion-Derived Ship Service," H.N, Robey, H, 0 . Stevens & K. T. Page, Naval Engineers Journal. Mav, 1985, [6] "Advanced-Cycle Gas Turbines f o r Naval Propulsion,"

Thomas L, Bowen and Daniel A. Groghan, Naval Engineers

Journal, May 1984.

[7] -Propulsion Powered Electric Guns; a Comparison of Power-System Architectures." Timothy J. Doyle and Guy F. Grater.

Naval Engineers Journal. May 1992.

Naval E n g i n e e r s J o u r n a l . M a y 1993 223