Destroyer seakeeping: Ours and theirs

Destroyer Seakéeping:

Ours an Theirs

by Captain James \V. Kçho. Jr..

t ...

In 196. while stea,nin

in beaz') u'eather ¡nt,i head

seas, the co,n,ninder of a L'. S. .\az'3 desír'i'e,- squadron in the

's1editerranecin tzoted his 1)1)-4.. flD-2, and DD-10 class

destroyers taki?lg solid green water ozer the bou' and zer heavy

spray on the bridge. The .Soz'iet Kot/in-dass destroyer

operating in close pro.vimitl' to the carrier task group appeared to

be taking no water oz'er the bou' and on1

occasionalI)' raised

spray aboie the fo 'c's le deck edge. L'. S. sailors u 'ore foul

weather gear and stayed off the fo 'c 's le: Soviet sailors paraded on

the fo 'c's le in their shirtsleeves.

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-The Soviet Navy first deplored a small s1uadmn of destroyers to the Mediterranean Sea for part of the rear

in 1964. and then again in 19o'. In

19.

a permanent

Mediterranean squadron was established. Since the dc-plorment of these Soviet naval torces to the leditcrra-nean, there have been an increasing number of reports from the U. S. Sixth Fleet staring that Soviet destroyers appear to have better seakeeping capabilities than U. S.

destroyers.

One former carrier division commander voiced his concern. On several occasions during heavy wearher his destroyers appeared to be more restricted in course and speed than Soviet destroyers because of their poorer seakeeping ability. While steaming on a course that

put the wind and sea on the

beam, his destroyers appeared to roll considerably more than trailing Soviet

destroyers. When he altered course into the sea to

reduce excessive rolling, his destroyers reported

fre-quent slamming and heavy deck wetness.

Simulta-neously, he observed that trailing Soviet destroyers' appeared to be riding well and were fairly dry.

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______,e--lt was this oflicer's opinionan opinion generally

shared b other fleet operators that Soviet destroyers

liad seakecping capal)illties which permitted them to take more wind and sea on the beam without excessive rolling, and to proceed into rough head seas at greater speeds than U. S. destroyers without experiencing as much deck wetness.

In response to Fleet reports of this type, several early Naval Ship Systems Command studies had compared the relative seakeeping capabilities of U. S. and Soviet destroyers. However, these studies were made with only limited -information available on the hull details of Soviet destroyers and prior to the development of an adequate theory for predicting ship-motion in a seaway. Generally, NavShipSysCom limited itself to a compari-son of deck wetness characteristics based on an em-pirically derived criterion for minimum required

free-board, and made rio comparison of slamming and

rolling characteristics. When U. S. and Soviet destroyers of similar size -were compared by class or design, studies

indicated that about as many U. S. destroyer classes

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28 _{U. S. Naval Institute Proceedings. November 1073}

as Soviet destroyer classes possessed good dcJ wetness characteristics.

Within the, past several years, ship morion theory

has corne of age and is now adcuare for predicting

the motions of conventional hull forms in head seas.

A practical implementation of this theory, the YF-17

Ship-Motion Computer Program, has been developed by the Naval Ship Research and I)cvclopmcnr Ccncr. (NSRDc), Carderock, Man'land. In addition, the Naval Ship Engineering Center (NavsEc), Hyattsville,

Mary-land, has developed approximate procedures, based on

the YF-17 Program. to facilitate estimating the se:ikeep-ing characteristics of a ship in head seas durse:ikeep-ing her early design stagesa period when inadequate details of hull shape are available for using the \'F.17 Program.

It was with these newly developed ship-motion

com-puter programs that the study reported on in this paper was conducted by NavSEC with support from NSRDC.

This study attempted for the first time to compare the

slamming and deck wetness characteristics of U. S. and

Soviet destroyers in North Atlantic head seas. Results

reported for the North Atlantic were applicable for the Mediterranean Sea and Pacific Ocean in that, while the absolute performance of individual ships varied, the relative seakeeping performance of the ships remained

unchanged. Since ari _{adequate analytical prediction}

method was not ayailable for making a co!nparative

analysis of rolling characteristics in beam and

quarter-ing seas, the study was limited to.esrablishquarter-ing the _use

of active fin roll stabilizers both by U. S. and Soviet

destroyers.

The principal features of a ship design that influence her seakeeping ability are shown in Figure 1. Ship size

and hull form or shape are the two features which most urc I. Major seakeeping design factirs

KNUCICLE ANGLE 0U1801JS BowsizE : R OUNON L SS

aifutt scakecping .lI)ilirv. A ship's size, particularly her length and diplaccrnen, his the greatest single

influ-ence 1)11 _{lier seakeeping ability. Generally, a large ship}

reacts less violently in a given sea state than a smaller ship, except when subjected to swells ofparticular wave

lengths wlikh cause a resonant response. It should,

therefore, be expected that the pitch and heave

mo-tH)ns, and hcnic the slamming and deck wetness char-actcristics of a 550-foot, 7,500-ton frigate would be considerably better than those of a 400-foot, 4,000-ton

destroyer CSCOrt.

The influence ola ship's hull form on her seakeeping characteristics can be best understood by considering

separately

_{her underwater and above.water}

charac-teristics. lt is the underwater hull form that principally

influences the pitch, heave, and roll motions ofa ship

as she reacts to a given seaway. Such hull form features as length, draft, beam, prismatic and midship section coefficients, lorgitudinal centers of buoyancy and flota-tion, as well as the addition of bilge keels, active fin stabilizers, or a bulbous bow, influence a ship's motion to varying degrees. These same factors also strongly influence a ship's resistance to forward motion, her maneuvering ability, and her intact and damaged stabil-ity characteristics. Hence, a ship's underwater hull forni is often a compromise between conflicting

require-ments, of which seakeeping ability is but one

con-tender. The compromise in hull form may be extended even beyond the basic hvdrodvnamic characteristics of

the hull. Such is the case in the frequent choice of

a fuller hull form in order to provide additional volume in the ship. This is a compromise dictated by the fact that modern destroyer designs are volume-limited and nor weight-limited.

Once a ship's underwater hull size and form have

been established in the design process, the ship's

mo-tion and slamming characteristics in a seaway have been

largely predetermined. Nevertheless, the ship's above-vater shape. while it does not significantly influence

the ship's motion, dUCS strongly aflct her spray and

deck wetness characteristics, The freeboard near the

how, particularly at the forward perpendicular, is the

most important aspect of the ship's above-water shape

with respect ro taking water over the bow. Other

features of a ship's above-water shape, which primarily aflèct her splaY characteristics, _{are the flare of the bow,}

the use of a knuckle or spray rails in the how,

_and

the roundness of the how at the stem. Unfortunately,

since thete is no analytical method for predicting a

ship's spray thar:icteristics, clic srud- discussed in this paper. was limited ro a comparison of deck wetñcss resulting horn green water on the deck.

'('his. latest NarSIC _{study compared the seakepin}

(See Figure 2). The comparison was nude of

t heir

predicted relative slamming and deck wctncs

itai-ae-teristics and their use of roll stabilization fins. Tite

information required for the Soviet destrovei-s was

ob-tained from Janes Fiqhtin&' Ships.

1ï'2-7L

lF-er's

Warships of the World. ¡973. and other -unclassified

sources.

In those instances where two destroyer classes were

built to the same hull design, such as the DD-i and

the DDG-32 or the Korlin and the Kildin. they were considered as one class for titis seakeeping study. Also shown in Figure 2 is the year the first ship of a class was completed and the number of hulls of that class known to be in active service in the fall of 1972. A total of 197 U. S. and 200 Soviet destroyer hulls were compared in the study. The World \Var Il DD-10 class still represents one-third, and the newer DE-lo-to and DE-1052 classes represent one-quarter of U. S. destroyer

hulls.

Slamming results from extreme pitch and heave mo-tions. Ir occurs when the bow of a ship, moving into

rough head seas, rises high in the water so that the

forefoot and keel emerge and then re-enter the water

with such force that the whole ship shudders. This

phenomenon is called "bottom slamming." Slamming can also occur when the forefoot does nor emergethis is known as "bow flare slamming." Since there is no analytical method available for predicting bow jlare

slamming characteristics, this study -considered only

bottom-slamming. Generally, for slender high speed ships, with modest bow flare, bottom-slamming is the more severe of the two.

The above description of slamming is too qualitative for analytical purposes. Hence, the criterion used to define a slam for comparative purposes was that a slain occurs when the forefoot and the first 15% of the keel aft of the bow emerges from the water and then

re-enters with a vertical velocity relative ro the water

surface greater than a certain threshold value. In

addi-tion, it was assumed that a ship heading into rough

head seas at maximum power would reduce power as required so as not to experience more than one slam per minute or 60 slams per hour. Rough head suas for a given class of ship were considered ro he those seas above the significant wave height or sea statu where

that class of ship, moving into the sea at maximum

power, first experienced one slam per minute. While these values were arbitrarily established for tite purpose

of making comparisons, they were nut thoughut Cu he

unreasonable. Separate additional calculations showed that the study's final comparati results were not very sensitive to these assumptions.

:. The comparison of slamming characteristics was

D.troyer Soakeeping: Our, and TheIr, 29

based on tite predicted average maximum attainable speed of ea ii class of dcsroer in North Atlantic rough

head seas. Fhis comparailve figure oí merit for sl-am-ming was called tite "average maximum rough water speed." lite procedure was essentially one of calculating the average speed performance of a ship, as increasingly higher head seas were experienced, from the time she

first liad to reduce her maximum speed to avoid ex-cceding one slam per minute until tite highest sea states were icached. A ships average maximum rough water speed represents the ship's average speed only in those situations where the ship must slow down because of slamming in head seas. Hence, a ship's annual average maximum speed for all situations would be consid-erably higher.

The results of these calculations are shown in Figure 3. The average maximum rough water speed for each destroyer class was plotted in relation to a ship's length at the waterline. The five U. S. destroyer classes wich the large SQS.26 bulbous bow sonar dome, representing almost one-third of U. S. destroyer hulls, were so slam-sensitive that they fell along a trend line which was about two knots less than the trend line for U. S. and Soviet destroyer classes without a similar-sized bow dome. With no information available to the contrary, it was assumed that there ai-e no Soviet destroyers with a bow-mounted sonar dome the size of the SQS-26.

This two-knot average maximum rough water speed reduction for U. S. destroyers with the SQS-26 bow dome was the only significant difference observed in the comparison of the slamming characteristics of U. S.

Figure 2. L'. S. and U.SS.R destro )-ers

US CLASS OD 692tRAM Il l9. OD710tRAM I 1945 DE 1006 1954 OD 931 I DOG 32 1955 DO 936 / DOG 31 1956 0(1033 1959 DOG? 1960 DIG QMOD. 1960 DLG 16 1962 DLGN25 1Q62 DE 1037 1963 DE1040 IDEG 1 1964 DLG 26 1964 DLGN35 1967 0(1052 1969 36 197 flNhsS%Y SJIT SMISSRVICS t&L

HUU.S USSR CLASS YEAR HULLS SKORVY 1949 24 63 KOLA 1050 6 3 RIGA 1952 34 3 TALL IN 1953 i 15 KOTLIN I KILDIN 1954 31 4 KRUPNY I KANIN 1959 8 23 PEÌYA I & I I 1961 45 10 KYNDA 1962 4 9 KA 5H IN 1963 15 i MIRItA 1964 21 2 KRESTA I 1967 4 16 KRESTA II 1970 4 9 KRIVAK 1970 3.

U. S. Naval Int1tute Proceedinge. November 1973

Figure 3. Slam,ni,,c,' conp.:ri.*ioz

and Soviet destroyers. However, it should be noted that, while the SQS.26 bow dome necessitates greater speed reductions in the speed range below about 20 knots, model tests and full scale experiments indicate that it can actually improve a ships slam-limited speeds above 25 knots. Other U. S. and Soviet destroyers, of similar length and sonar dome configuration. appeared to have similar slamming characteristics as indicated by their comparable average maximum rough water speeds. Deck u'etness was defined as occurring when the bow of a ship moving into rough head seas plunges into a wave and the water rises above nie edge of rite deck

at the bow and washes aboard. like slamming. it

is

a result of extreme pitch and heave morions. The

frequency of occurrence of deck wetness tr a ship of a given length moving into rough head seas an a given' speed is directly related ro the amount uf freeboard at the forward perpendicular and w1II(h lias been cxtendd

aft with a reasonable sheer. In thepasr several cars.

NavSEC has developed a proposed new freeboard

rire-non. It is premised ofl a simuliTineous failure philoso-phy which provides for just enciugli fredoard to resuh

in a ship's experiencing one dc&k wetness ¡;er minute during those times she e.xperienLcs one slam per

miii-ROUGH WATER SPEED IN HEAD SEAS VS.LENGTH

US SHIPS NO SOS - 26 BOW DOME

L US SHIPS SOS -26 BOW DOME

O USSR SHIPS (NO LARGE DOMES)'

ute. Since there is little that can be done about

slam-ming once a ship's underwater hull form has been

chosen, this criterion, which is applied at the average maximum rough water speed. precludes both under-or over-design from the deck wetness viewpoint.

The basis for comparing the deck wetness charac-teristics of U. S. and Sovier destroyers was the compu-tation of a freeboard figure of merit for each destroyer class. This was done by calculating the freeboard

re-1uircd for each destroyer class

based on the new

NavSI( - fFcCbO:If(l criterion and then calculating, rela-tive to this reuircd freeboard, the pèrcentage of actual freeboard with which each destroyer class was built. ThUS, a destroyer that. was calculated to require 20 feet of freeboard. bun actually was built with only 18 ker. had 90r of her required freeboard. Her freeboard figure

of merit (or freeboard factor),. cherctre, was 90.

Shown in Figure 4 arc the results of calculating the treehiuoi !igurr of merit fur each destroyer class. As. shown. ¶11e average freeboard ttctor for all class- wa 92. with t-ah class (ti. S. and Sovier ranked in relation

to this conibincd g ï'hose ships aho'e thc class

average. lute, were consIdered dritt chan average and

those below, etter.ch4I1

)f iJie eight [I. _{S. and seven Soviet destroyer classes}

20H I.-o

z

o Ui

15-u, Ui I-' lOr-PETYA (NO 0E 1033 O RIGA US-USSR TREND K VN DA

LARGE DOME) KRUPNV O

KOTLIN O

-KAIVAKØ DD71O O___. _{DOG 2}"KASHIN

DD692,3.- ci OD 931 _- SKORVY o DE 1006 _A. _{DE 1052}£ KOLA

A.

DE 1040 ,_..-DE 1037 DLGN 25 DLG 16,,. LGNB

I-_

%G 9

..'4LGN35 KRESTA 26 00963 US TREND WITH SOS 26 BOW DOME

300 350 400 450 500 550

which were drier than average. only three U. S. and four Soviet classes were built with trechoard cju;Il to

or greater than that which the new avStc freeboard

criterion would have required.

Of particular interest were the low freeboard figures of merit for the DD-10, I)E-1040, and I)E-1o52 classes-those destroyer classes which represent nearly 60% of all U. S. destroyer hulls. Interesting, also, was the low freeboard figure of merit for the Soviet's newest guided missile destroyer, the Krivak, which is about as defi-cient in freeboard as the DE-1040 and DE.1052. Only three Krivak hulls are presently known to be

opera-tional, but if the Soviets build a number of hulls in

this class without adding a bulwark to the bow as they have done previously to the destroyer escorts of the Pena and Mirka classes, the effect will be to lower the Soviet average freeboard figure of merit.

The result of considering the number of hulls built in each destroyer class is shown clearly in Figure 5. When destroyer classes were compared, nearly half of both the U. S. and Soviet classes were drier than the combined average. This also was the conclusion drawn from previous studies. But, this conclusion changed significantly when a comparison was made in terms of the number of active U. S. and Soviet hulls in each

e

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Daatroyor Soakeeping: Our, and TheIrs 31

destroyer class. The comparison showed that 65% of the Soviet hulls and only 30% of the U. S. hulls were drier than tue average. This means that fleet operators have better than a two-to-one chance of seeing a Soviet destroyer with better deck wetness characteristics than a U. S. destroyer

The U. S. deck wetness comparative position will improve with che continuing removal of the remaining DD1IocIass destroyers from active service. It could also

be improved significantly by the addition of 4-foot

bulwarks to the bows of the DE-1037, DE-1040, and DE.Io2-class destroyer escOrts. The addition of spray rails to the bows of these ships would also improve their poor spray characteristics.

Roll stabilization of a ship can be achieved by the use of bilge keels, active fin stabilizers, and either active or passive roll-stabilizing tanks. A review of the infor-mation available on U. S. and Soviet destroyers indi-cated all classes were fitted with bilge keels, none of them used roll-stabilizing tanks, and fin stabilizers were fitted ori three U. S. destroyer classes and nine Soviet destroyer classes. A summary. of these data is shown in Figure 6.

At speeds above approximately ten knots, fin

gurc 4. Deck U"etes.s (freiboar/fzi'r)

32 - V. S. Naval Institute ProcoedIng November 1973

lizers can achieve roll reductions of 5O _{or greater on} a11 course headings. They are generally ttted on de-stroyers for one or more of the following purposes:

I To ensure adequate weapon and sensor system

per-formance during specific wind and sea conditions vhen such performance cannot be effectively accomplished by bilge keels and local system stabilization alone.

To improve overall ship system operational perform-ance under all wind and sea conditions by minimizing poor operator and equipment performance attributable ro excessive ship motion.

To improve the overall quality of shipboard habita-bilirv by providing an environment free from excessive ship motion.

Information available indicares that it is standard

practice to fir active fin stabilizers on all Soviet destroy-ers, whereas they arc used on L. S. dctr..-cr 'ml...hen

required for adequate weapon and scn',o perfbrrnance.

This means that fins are ñrred on

o" of Sovet

de-stroyers and only 3O of L'. S. destroyers. Hence. Eìect operators have better than a two-to-one ch-anc of ce-ing a Soviet destroyer with active fin roll stahllj,4tj(>n than a U. S. destroyer so fitted.

A way of integrating the Interaction o? lmmin.

deck wetness, and roiin behavior m'o an ovcrfl ;re

diction of comparative seakeeping cdpahiIt

_{i- nr '.cr}

available. However, an attempt wa m.dc 'o 'hU'.A he

-effect of this in'reractioii in a 9ualìrarlve manner by the

u of an na1vtmcal prediction tCJJflI9..1C Ah!t}l

puied a hgure of merit c4led..Comparai..c Annu.J

Average Maximum. Speed r

r: S

The procedure for detc:mining was based on

.2fl assumption that a ship was ,perted mn the N',rtj:

t\tl.lfltI( _{dutiiig an anriuil cycle uf all earlicr}

coidm-tiOfls and at tue maximum speed attainable WItIL()Ut

cxccc(1In4 more than one slam or deck wetness per

minute. A furihcr assumption was made that ships

without fin stabilizers would have to operare in head seas more often than ships with fin stabilizers owing

ti) course changes Into the sea made in an eff)rt to

reduce CxCcive rolling. As a resul, ships without fin

stabilizers

li ...ro reduce speed in head seas more

often because of slamming and deck wetness. To

en-sure a fair seakeeping comparison between de-strover classes, whose maximum calm water speeds varied over a wide range, all ships were assumed to have exactly enough power installed to make 30 knots maximum or trial speed.

The results of these calculations are shown in Figure 7. Each ship's CAAMS was plotted in relation to her length. For reference purposes, "approximate good

practice lines," with arid without fin stabilizers, were established based ori calculating what the results would have been if none of the ships had deck wetness prob-lems or large bulbous bow sonar domes and, hence, had to reduce their maximum speed only because of slamming.

The results indicated that ships with fin stabilizers,'

particularly those under 450 feet in length. enjoy a

performance advantage over those ships fitted only with bilge keels. The results also showed the effect ori per-formance of ships with deck wetness problems. and in the case of the DE1j3, DE.io4o, DE-:5, DLG-:O, and DLGN-5. che additional effect ori performance of a large bulbous bow sonar dome.

The impression derived from this overall seakeeping cr)mpanson was that Soviet destroyers Cnjov relatively better seakeeping capabilities than L. S. destroyers.

- Figure 5. 1)ek Ll'etnelc (b) Jaiies and h, hIIm bii1t)

r 15 13

f

FREEBOARD 'ACR5 BY LL5S FR8RD FACTOR '% _USSR FR Et B OAR D FAC ICA 't' M IRKA PETYA I & II 109 w8 98 '93 R IDA

«u

108108

t

DRIER KASHI. 93 92 KR(STA II 92 '92 L /EA'GE KRESTA I 90 KRUPY/KAi.Is _'iETTER K 011. IN f K ILOIN 90 KYNDA ₈₈ 87 KR IVAI( 87 86 TALL IN ₈₁ 73 SK OR Y? 78 Us 1033 9360DG31

I7

35 .626 616 CR 931!DDG32 EG I 6 RAM Il 71OFaAM i

'28

Figure 7. O:rall seakeeping comparison

PETYA MIR KA DE 1033 APPROX. GOOD PRACTICE LINE W/ROLL

STABI L I ZAT ION

\

DE 1006

O KOLA

O RIGA

300 350

An attempt WaS made to 1tiantttv in i zencra! way

the advantage of the good seakeeping ahiliv enjuved by Soviet destroyers. A scenario was enisioncd wherein

two groups of destroyersa squ:idron ut 25-tout.

4.000-ton destroyers, and a squadron cit similar-sized

Sos-jet destroyers raced toward a military ol)}ective

1.500 miles away. The Soviet warships were equipped

with fin stabilizers, the American ships verc nut. It

was assumed that the maximum calm water

speed

available for both groups was 30 knots and that their respective courses placed the wind and sea on their

beam. It was further assumed that the weather was

deteriorating, and that each group altered course when tolling in excess of 15 to 20 degrees was experienced and slowed when slamming or deck wetnesses in excess of one per minute were experienced.

The results are shown in Figure 8. The sea state

encountered is shown on the horizontal axis, time to reach the objective is shown on the left vertical axis and time late on the right vertical axis. Data available

for such calculations indicated that, as the weather

deteriorated and Sea State 5 conditions were

experi-KRIVAK PI DE 1040 DE 1037 A oSKORVY DD 710 DD 692 K ASH IN KRLJPNY KOTLIN DE 1052 A DDG 2 DD 936 O TALLIN

.

OD 931 KRESTA II KRESTA

COMPARATIVE ANNUAL AVERAGE MAXIMUM SPEED VS. LENGTH

\

_APPROX.

GOOD PRACTICE

LINE W,'O ROLL

STABILIZATION DLGN 35

t

DLG16 I

e

-

.0

8 *DLGN38 e DLG9 0L026 DLGN25 DO 963 DLGN 36

A SHIPS W/FIN STABILIZATION

SHIPSW/O FIN STABILIZATION

USSR SHIPS

O USSR SHiPS

I I

--400 450 500

LENGTH (FT)

Destroyer Seakeeping: Ours and TIiofr

ISig u re (i. ( lasses fil lesi u/I/s f,,, st,/,ilizers

3's

US YEAR YLS NO USSR YEAR YES NO

DO 692 IRAM II 1944 X SS 0kV V 1949 X OD 710 FRAM I 1945 X KOLA 1950 X DE 1006 1954 X RIGA 1952 X DO 931 / ODO 32 1955 X TALL IN 1953 X DD936/DDC31 1956 X KOILIN J KILDIN 1954 X DE 1033 1959 ' X KRUPNY I KANIN 1959 X

DOG 2 1960 X _{PETYA I &} Il 196] X

DIC 9 1960 X K YNDA 1%2 X DLG 16 1962 X KASHIN 1963 X DION 25 1962 X M I RKA 1964 X DE 1037 1963 X KRESTA I 1967 X DE 1040/DEC 1 1964 X KRESTA II 1970 X DLG 26 1964 KRIVAK 1970 X DLGN 35 1967 X DE 1052 1969 LI

34 U. S. Naval IntItuto l'roceodlnge. November 1973

enced. the LT. S. destroyers lud to comiliun. e dìaning

course to reduce rolling. and hoit k t liere;ther rcduLe

speed because of deck wetness or shimming. Iliuse U. S. destroyers with deck wetness prubkm or a large how

dome obtained plotting positions R) the kit side of

the band spread shown; destroyers with adc1uatc free-board that slowed only for slamming obtained plotting positions to the right of the hand spi-cad.

The results showed that the Soviet destroyers did not have to commence course chanies until Sea State 6 conditions were experienced and then they, too, had to reduce speed because oí deck wetness and slamming when headed into the sea. The Soviet destroyers, with less deck wetness problems than U. S. destroyers and without large bow domes, plotted towards the right of the band spread shown.

The answer as to which destroyer group reached the objective first was obvious. This example. qualitative in nature, demonstrates, in a general wa, an advantage that may be enjoyed by Soviet destroyers with better scakeeping capabilities than U. S. destrovets.

There are those who would challenge the assump-tions of this scenario and would have had the U. S. destroyers maintaining course and speed until in ex-tn'mis. Left unanswered by this course of action,

how-ever, would have been the ability of the crew, and

perhaps the ships, to fight effectively when the objective was reached.

A logical question to address before concluding the study was how the seakeeping characteristics of new U. S. destroyer designs compare ro present U. S.

de-strovers. With regard to their slamming and deck

Figure 8. Operational adz'an:age of good seakeeping

66 62 SEA STATE WAVE HEIGHT SFT 5 lOfT. S 15F?

\-ctncss diari. tc:rist ILS in head seas, the question WAS

investigated in two wa s. The first method was to

compare the Patrol Frigate PF), DI)-'X., 1)LGN-3(., and

I)i. ,N.!.s designs with selected U. S. destroyers of simi-lar length and dispsimi-larement using the NSRDC \'F-17 Ship- Motion Computer Program. The second method, the results of which are reported in the Summary, was to compare these new designs with present C. S. and Soviet destroyers using the \avSEC developed estimat-ing procedures.

The YF.1' Computer Program

requires detailed

technical information. Since some of this information was not accurately known for the Soviet destroyers they

were not included in this portion of the study. The

SRDC Program was used because it provides a more definitive comparative analysis than the NavSEC pro-gram, such as the prediction of the maximum wave height or sea state in which a ship can operate while heading into the seas at various speeds before exceeding one slam or deck wetness per minute. It was thought that this type of comparison provided a better repre-sentation of realistic operational situations.

The results are shown in Figure 9, where the ship's maximum wave height capability in North Atlantic

head seas at 20 knots is plotted in relation to ship's

length. The percentage of annual occurrence for each significant wave height is shown on the right of Figure

9. Ships that had to slow initially because of deck

wetness are shown as circles and those that were initially slam-limited, as triangles.

Comparison between new designs and present de-stroyers was done bs' comparing ships of similar length

20 FT 16

t

î

TIME - LATE OBJECTIVE 1500N.M.

I ---- .., .--

.---

-?

--- z-..--- :- .. .... ....__;.-' - - -

-..

.-.-- - -.. J - - ___-p, - -

--r

_{-: --.,---}

_--

-t

'---

.

---.-'-.

-and displacement. Thus, a comparison of the 3,400-ton PF with the 4,100-ton DE-1057, the 4,100-ton DI)-9ó, and the 4,400-ton DDG-2 indicated that the PF compares very favorably in slamming and deck wetness charac-teristics. She was also the only one of the four ships that was initially slam-limited. As a marrer of interest, the improvement achievable by the addition of a four-foot bulwark to the bow of the DE.t052 was also calcu-lated. The results showed the DE-1052 would become slam-limited at a higher wave height. but would still fail short of the PF, the DD-9.ó, and the 1)i)G-2, mainly because of her large SQS-26 sonar dome.

The slamming and deck wetness characteristics of the 7,600-ton DD-93 compared very favorably with the

<

G

. 4

2

_-_7_'--7,600-ton DIG-ic, and the 7,900-ton DLG-2. while-the 10,000-ton DU:;N-, and the 10.500-ton DLGN.8 com-pared very well with the 9.100-ron DLGN-;5. lt was noted that under the new N.1vsic freeboard criterion.

the I)IGN-c and L)I.c;N-8

_{could use about tur more}

ket of freeboard. However. rhc ships. because of their

-size, will seldom experience occasions when they may have to reduce speed below 20 knots to avoid excessive deck wetness in Nôrth Atlantic head seas. As indicated in Figure 9, these occasions will occur less than 3% of the rime during an annua! operating period.

Iksin studies indicated that the operational

re-(juirements for the PF. l)t)-%', 1)LGN-, and DLGN-'s weapon and sensor system performance during specific

:

-q

;--.-;1.j--.

--

_Iç__t

-"',::--

_'-..-:.

'

- '--a-.

-- _-.-

-'

----.--:

_{- - -.: ---z-- -- - -.} -- . -

;;-:

j:

--d

'n

-

'-- '--'--.

.- -. .--

--.-.-.--.&---r& :

)

36 U. S. Nava] Institute Proceedings. November 1973

Figurc 9..¿u LS. desiçis

25 - AVG.MAX ROUGH WATER SPEED SLAMMING US-USSR TREND

-.--.

(NO DOME)

MAXIMUM WAVE HEIGHT CAPABILITY IN HEAD SEAS AT 20 KNOTS

600 FREEBOARD FACTOR loo HULL AVG 118 DLGN 36 O---. 300 350 400 450 500 - 550 600 LENGTH (FT.) Figure 10. Su7nmar-9 70L 2 5 15 50 95

DECK WETNESS ACTIVE FINS

NO FINS PF DO 963 DION 36 DLGN 36

I

90 _HULLS -MTH FINS-30 80 f., (n(n 'f. a 0O z r., -1 O z w -J o 10 I. 70 DD936

000G2

PF

DLG-'

°5iIGN 38 OD 963

-

nIrM DE 1052 W/4' BULWAR 'TREND LINE u.' O DE 1052

I-(

DE1033 O DD 710

o DECK WETNESS LIMITED SHIPS -A SL-AM LIMITED SHIPS

6

wind and sea conditions vcre such that their rec1ujred roll

characteristics will be achieved effectively with bilge keels. Hence these ships will be fitted with bilge keels.

Summary

In summary, the results of this srud', as shown in Figure 10, tend to confirm the observations of Fkct operators that Soviet destroyers appear to have better seakeeping characteristics than present U. S. destroyers of comparative size.

They showed that U. S. and Soviet destroyers of

similar length and sonar dome configuration have simi-lar slamming characteristics in terms of average maxi-mum rough water speed. However, U. S. destroyers fitted with an SQS.26 bow sonar dome have poorer slamming characteristics at normal cruising speeds than U. S. and Soviet destroyers of similar size without such a dome. The slamming characteristics of new U. S. designs were predicted to be comparable to present U. S. and Soviet destroyers of similar length and sonar dome configuration.

The results of deck wetness comparisons indicaced

that fleer operators have better than a two-to-one

chance of seeing a Soviet destroyer with better deck wetness characteristics than a U. S. destroyer. Soviet destroyers are not designed with better deck wetness characteristics than U. S. destroyers, b-ut the U.S.S.R. has chosen to build more hulls to designs having good deck wetness characteristics than has the United States. However, the U. S. deck wetness comparative position

could be improved significantly by the addition of

4-foot bulwarks and spray rails to the bows of our

DE-1037, DE-1040, and DE-1052 destroyer escorts. Of

par-ticular importance was the fact that the deck wetness characteristics of the PF and DD-963 should show

sig-nificant improvement over present -U. S. destroyers.

And, while the DLGN-36. arid DLGN-38 could use ad-ditional freeboard, in reality they should not experience any significant deck wetness problems because of their size. In addition, the development of the new NavSEC freeboard criterion should ensure that future U. S.

de-At a British naval barracks the enlisted men were being given their shots prior to going

- overseas. One cheerful Scottish hd, having received his series of injections, asked for a glass

of water. "What's the matter, Mate?" asked hc sick-bay attendant. "Do you feel faint?"

"No," replied Juck. "I just want to see if I'm still watertight."

Contributed by Lloyd Scow Cram

/

Scorch and Water

Deatroyer Seakoeping: Our and Theire 37

stroyers arc designed with satisfactory deck wetness

e ha ract er ist i cs.

The fact that Soviet destroyers are fitted with fin

stabilizers as a standard design practice to improve

overall ship system operational performance, while fins are fitted on U. S. destroyers only as required to ensure adequate weapon and sensor system performance, was

ari extremely interesting comparative finding. This

means, with respect to

roll stabilization, that Fleet operators have better than a two-to-one chance of see-ing a Soviet destroyer with fin stabilization than a U. S. destroyer so fitted. This situation will worsen in the

future as active fin stabilization is not presently

in-cluded in new U. S. destroyer designs. Ir would there-fore appear useful for the U. S. Navy to conduct the research necessary ro quantify the effectiveness of using active fin stabilizers. The effectiveness measured should include the improvement in overall ship system per-formance, including operator and equipment interac-tion and the tactical maneuvering advantage in terms of course and speed. lt should also include the increased opportunity for underway maintenance and repairs, and the improvement perceived by sailors in the quality of shipboard habitability. The results of this research could then provide the basis for future decisions regarding the use of roll stabilization in future ship designs.

Generally, it appears reasonable to conclude that the Soviets place high priority on good seakeeping capa-bilities and that the' are willing to pas- the price for these capabilities.

Commissioned through the ROC program in 1952 aIrer receiving ¿ B.S. in Mathematics from Stonchill College. Massachusetts. Captain Kehoe holds an MA. in Education trotti San Diego Scare College. His sea durv included

tours ¡ri thc Nuclear '«'capons Division. USS ¡rap (CVA.lS) and L'SS

Kearsarge (CVA.33) as operations officer. USSRsth(DDR-7l4) executive

officer. USS Farrrngran (DD-843): engineer officer USS Wasp (CVS.18); and commanding officcr.L'SSJahn R. Pien-e(DD.753). Ashore, he had duty in nuclear. weapons. the Polan misi!c program, and instructing in pro'ecr management. He s currently at rhc Naval Ship Engineering Center. Hvatrs-ville. Mars-land.

The author grirefullv acknowledges the assistance of Dr. R. Johnson,

J. Raber, K. Walkt. L. Smith. nd P. Gale of NavSEC, Hyatrs'iJle,

Mars--land, and L M,,tcer of NSRDC. Carderock, MaryMars--land, irs conducting this

-rhc letter to which I 'teter is onC of rrianv paj-'ei whih mv v

ti .ini I tiitil

upon the ck-ath

c:ilniIhk-

I.iiL-s

l:ist direct dcscndant Mis. I]iiIhIi h

Balie. in lO('S.

hss Iihc

w:i nv

-svite's S( clisiri. The -'lkt iOn

fl-ludcs personal Ji.tnes ot ( otn n.m der

Bache from dic .mmz ,s S viicii lic was

captamns clerk in the

.Str.iti.

letters to his mother durmnc and after

the Civil War. the (lass of S vc.mr

book. .Iiir ?;iP/v a/./ /'/'. scv.

eral hooks by Admiral Porter. nid ni.iiìv phc'roraphs. Now known iS t lic Collection. it is in the Special Coflec-tions sectiOn ot Nimirz Library.. where it maY prove to be in interesting com-plement zo the Pn;..c'./icg. own sou ces of Civil \Var naval history, described by Professor Heitzmann in the Professional Notes section of the Anniversary issue. Other parts of the Bache Collection were donated to the Historical Display

Center at the Washington Navy Yard

three rears before Miss Bache died. In-terestingly enough. mv friend Roy

Smith became-Director of the Center

shortly thereafter.

"Destroyer Seakeeping:

Ours and Theirs"

(Sed. \V. Kehoc.Jr.. pp. 2&-37. November 1O3

Proczrdi7zgi)

Lthitsnant William R. Nicho/$. J. ( S.

Nat-al Rserz'e (Reiirea')Captain Kchoc's

article deals with a problem that has

plagued destroverrnen since the rda-rively small, high-speed -combatant ship appeared onrhe scene. I would like to

comment on the head seas aspects of the - problem, offering some qualitative

corn-mënts about shedding the water once it has gained the deck, and the effects

of the water-while ir is on deck and the process of running or blowing dear.

-I was on active duty at sea, .vhen jet. airrraft had joined the Fleet, but before

there were steam catapults on aircraft .'carriers. A combat.lôaded jet aircraft - required a relative wind speed of about

40 knots to get off the deck. Plane

guards for individual carriers or the

en--rire ask force and screen- would steam

ro achieve 40 knots over. the deck. --A

mostcòmmon occurrence in the Pacific is the ocean swells derived from weather far removed by. time and disrancc. But

i he- sv:mvt :1( hOu 5\.iS ilicic mimi rut' force

iii.idt- its ()\vi-i -indsitli -fl) kiit)is acting

tin sii.itcrr .micr s\:i' i' li ICtI (iVi

'leek. lhis (-\.ii1ill(' is. r:l.1r mitt

i-nit t is Ui ix.iitìjlc itt iriiimrv. limilv.

Oil I jill .i)l,-F,it ii)ils -lmii li chu-s tint

pur-I-nil

idiiit

in of s'il l5i .iti"(' ill: v(t

duck etluits It is ,i iILvst iiiii ni mint

.itili,iz:11 .ill. or .ij'cr.1Iln :iitd tcccpting

the iiilsciltictLs. lt is -ei-rain rimai tlieiç

\Vili il-ivs he L-iluivalctlt Sit uJti)nS. l)uriiig i lie pmot.\X'orld

\\'ir

I 1/ -Ktiii:i j'.-ri \(l.i lieue \\'eIc si_yeral ,i4cfll-ra'

t kitt s nt siii;il hooks mud tact ici I pub-licitioiis. Suiic Tnerncirv recess iccalls one

nt the pLibs carriei a sign:il. ' Pr ceed

it maximum srued wit hour incurring

ti ips mie da ¡n .m,c.

Speed is one of the basic parameters in a ship's design and opei:ating require-merits. The naval architect and marine engineer design a hull form and

propul-sion to achieve the requirement. The

builder demonstrates over the measured mile that the rcql4ired speed has, indeed.

been achieved. The new class will go

into the books, probably something like "3O-plus knots, speed classified." The actual operational speed in a seaway may not be at all what the book says. Oper-ational speed is determined by weather, - operational imperatives and willingness to accept-levels of risk of damage to ship and injury to personnel.

There will, be times when she sticks

her nose in green water. The problem

is ro minimize the occurrenceand,

minimize the effects when it does occur.

With regard to shedding water, the

requirements are sheer. camber, and facilitating fhsvdown. over and off. The -newer freeboard considerations provide increased sheer where the main deck is a flush deck configuration.With araised

fo'c'sic deck, the sheer is not necessarily

adequate. This is in the realm of gross

hull configuration presumably deter-mined early in preliminary design. But

sheer must be given its due as a torand has been notably Icking on

-- sòme older hull designs. - -

Camber appears to suffer from time -ro time in thd name -of-p-roduction cost savihg's. Weather decks with no camber at all can he found. Camber must never

lose recognition as one of the prime ways co get rh water.off, particularly

-on the fo'c's'les of small combatants.. Sheer and camber have been arond

-- Comment ûnd Dtaeuø,aiOfl

sin(e tIme beginning of-ships and tcfar-ing. 'l'lii Sli()iild hc ('n)1)li,tSi/.ed. because

t }ierc is S') nl uch innovai ion.

sopliis-iiv-ai jein and itt her new apprxielies

(o(ìa\. titar there is a real risk of

discard-ili,g ilic ili. without adequately

cxamin-itig its neccssirv. validity. or the reasons .

-why it managed rit last so long.

-l'ue titirmi rcv1uircmcnt -is minimizing nhst rUCriL)il to low. There are two

ob-jC(i iV5 first. ro shed the water to get

the 'eight oíl and allow the bow to rise.

and tite sc1nd.. ti) shed the water in

as clean a flow of . vater as possible,

withouibreaking up into other blocks

of water or being driven back as spray. 'ruie term wet deck and the word spray may nor carry tile emphasis intended in

this discussion unless the emphasis is

supplied. The physical spectrum ranges from gross. solid water to mists' spume. -The effects range from nuisance value misting ofbinocular lenses to significant structurai damage. Damage to weapons

-is unusual, but not unheard of. The

more usual cases are-found in the rruddie somewhere. Yarying amounts of water

-running on and blown from the'wet deck degrades the effectiveness of all

topside watchsränders (including those

behind window wipers); Water and

spray degrade the effectiveness and ag-

-gravares the maintenance of all topside optical and repeater equipment for ship-handling, station keeping, lookouts, sig-naIling, and weapons control. Ir not just a matter of shirtsleeves versIs foul

weather gear on the weather decks, ir

is the fundamental matter- of the effec-rivet-tess of the ship as a unir.

Let's invent a term _fo'c'.''le cleanliness. Relative, cleanliness is the presence or absence of-equipment, fittings, or other

devices which impede the ckar run of

water off the deck and over- the side. In many ships. both naval and commercial,

one can see evidence, of designers'

thought having been given to this prob-

-1cm in. individual details. This writer has never seen anything addressing the problem of- the fo'c's'le as a design en-tity. Perhaps chis is the byproducç of the

unusual design -evolution. The naval

-architect provides, the hull formlet us

assumewith -. adequate sheer - and

camber, then, the other design groups proceed to clutter it ùp with their "re-h

quirements

the-)

: 96 U. S. Naval Inatitute I'rooeedings, March 1974

fo'c's'k? Foreward weapons: izround tackle and its mcchanic.il luitdling equipment; and mooring fittings.

What is usually found ouì

fo'c'sïe? In addition to that mentioned

in the previous ucstion. hatches: scur-des; mushroom ventilators: tire stations. complete with all accessory ge-ar: vents. sounding tubes, and overflows: life lines: jack stati; vent ducts and tans on house

sÏdes: assorted pipes and wircwavs; waterway bars: and an endless list. In

fact, the fo'c's'le seems like a handy place

ro put things on a space-limited ship. In recent years. a basic change has

occurred in fo'c's'le-mounred weapons-missile launchers. ASROC, and the newer

5-inch mounts. These are not

crew-served weapons. This change opens the door to a new look at fo'c's'le

require-ments. There is no longer a need for prsonnel continually on 4e fo'c's'le

deck underway. Arc lifelines really

re-quired? They are most efficient at break-ing up water into wind-driven spray, and

are excellent in collecting ice in sub-freezing weather. When not needed,

lifelines might be stowed, collapsible or otherwise removed. Safety rails and tag

lines, as. in submarines, provide safe access for individuals or small groups when lifelines are nor in place. In the

final analysis, ir may be determined that

lifelines are required. The trade-off

might not work out. Nevertheless, the opportunity exists for a new look at

fo'c's'le design. For a starr, a lot can be

lerned by looking over the shoulders

at the submarine decks. Subs have years

of experience at cleaning up

decks-though for entirely different reasons.

What are a few other candidates?

Mooring fittings can be faired in.

Water-ways are just in the way. \Vhv nor

radiused gunic? Anchor windlass and

- . associated controls can be grouped

be-hiñd a faired breakwater, thus sheeting off water instead of breaking it up into a dozen patches. Forward faces of Wea',-ons can be similarly faired. Bulwarks and breakwaters can go far towards ieducing the lifeline requirements and attendant

problems.

..

-Anchors can present problems pecu.

liar to small ships. The djstance from

shell bolster to deck bolster is very short,

': times all one casting. "B6v flare

slamming" will frequently drive water up through che hawse pipe without the

deck usd1 even going under. Anchors

rcccs-Ll in pockets. vitli remore oper-able covers. eluunuitue titis source of wet deck pioi1eiìis.

1)istributivc systems should not be

permitted to terminare on the fo'c's'le, unless such Leinìin:ition iS necessary to meet an operation requirement. A little more t hought can move a lot of

termi-nations elsewhere. lhey should be run

inside bulkheads and under decks. Forward facing bulkheads should be radiused. Consideration should be given

to concave radius where the bulkhead

joins the deck. The list of candidates is limited only by the imagination.

lt should be noted that destroyers produced shortly before World War Il

evidence many of these characteristics.

i.e., radiused house fronts, radiused gunwale, relatively free from clutter. In following years, however, spray-makers, under the name "improvements," have been added. Decks themselves have lost

out to "production economies." A lot

has been unlearned.

All canlidates for fo'c's'le installation must be approached with two questions:

Is

the location of this item on the

fo'c'sle mandatory to meet an

opera-tional requirement: and for each "must" installation, what can enhance shedding

varcr and minimizing spray?

Every item on tite fo'csle must first, be justified as mandatory, then, second,

the installation designed to minimize

the wet deck effect. A really thorough

approach would address the fo'cs'le as

a whole: an integrated design

consider-ing not only the individual elements, but their rel:irimships to each other to produce an optimum fo'c's'le design-the fo'c's'k' as an entity.

Some of the suggesttbns outlined will

cost moneyadditional cost in initial

construction. By adopting the clean

fo'c's'le ph ilosophv. however, many benefits can be gained simply by driving the philosophy with its dry ship oh1ec-cives down iflto detail design. The

re-sults will yield a dryer shipimproved

seakeeping ability; higher operating speeds is !imired by ve:ither/tacrie:tl conditions; teduced topside damage and mainiecunce: - and enhanced watLh.

stander performance. In. the long haul, increased initial costs nav pleasantly

surprise everybody by yielding mine

oferating effectiveness for che m(inev,

-- -..' .';P ,

... -

- .? .

¿.' " !

-': ç-,; .

'.

" r

4.'t:-,:-:'

New Soviet Warships:

.

Arc They of Superior Design?

(:/)/i-f Ra/,o Superi ¡cor k'únald D. Low,

Rì3't/ ,luctra/ian NatyA study of the

1973 Jone.c Fithting Ships shows noted

differences in naval policy influencing

current British and U. S. warship dc-signs. to those of the Soviet Navy. \\'hcn translated into hardware, these

differenccs become quite revealing in the Krivak and Kara classes.

The Soviet Navy is building its new cruisers and destroyers with a wide range of surface-to-surface and surface-to-air missile systems. The British and U. S.

Navies. however, continue to fit their

new destroyers and frigates with 4.5 and

5-inch guns. with no apparent SSM

capability commensurate to their Soviet Coun terparts. Furt hermore, guided mis-siles in their many and varied

configura-rions, were extensively employed by

both sides during the recent Middle East conflict, and the effective results achieved by these missiles. leaves little

room for doubt that they hare become

the main weapon systems for the future, br land, sea, and air forces.

- Is there any point rhen. in retaining

the 4.5 and 5-inch guns on new British and U. S. warships, especiailv the Type 42. Type S2. County-class. .DLGNs. the Sprzia.ice. Kno.v. and the proposed patrol frigate classes? In addition, on the new

Soviet ships. the largest gun now

mounted is the 3-inch (6-mm.). which

indicates that gunnery systems have

been relegated to a secondais role in

favor of SSM artharnent. Though effec-tive naval gunfire support was provided by allied ships during the Vietnam war,

is this reason for continued fitting of

4.5 and 5-inch guns. when n the tuture.

the "opposition" ashore in similar

cir-cumstances. will more than likely pos-sess an acti'e SSM capability?

Finally, if new British and U. S. war. ships are nor designed to éffeccivelv

en-gage in combat with ships of Krivak. Kara. Kresta. and Kvnda classes, then

how are they to be dealt with? The past ren years has seen the Soviet Navy de-velop and commission a number of re

-markable and advanced warship designs,

of which the Krivak and Kara arc the'

latest. In view of this progressive devel-opment, it would appear that the Soviet

-Navy may well have establshe an