75symp12_observation of ship damage over the past quarter century

8/13/2019 75symp12_observation of Ship Damage Over the Past Quarter Century

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o THE SOCIETYOF NAVALARCHITECTSANO MARINEENGINEERS, ..,C,, 74 Tr,nitylace,ew York,N.Y.,10006,+(ii *% Papert.he presentedtme ShpSt,.ct,eyrnpxl.m8 e~ Wmhi@on,D.C.,October.3 1975c+,% ?,~,,*,.+.Observation of Ship Damage overthe Past Quarter CenturyH. S. Townsend, Member, United States Salvage Association, Inc., New York, N.Y,

6>COPY@ht 1975 byTheSocietyfNavalAmh(tectsndM..,..ngineersABSTRACT

This paper treats with ship damagestaken fyom surveys of the United StatesSalvage Association, In. ., over the pastquarter century, on vessels of all flags.Insofar as U. S. flag vessels areconcerned, the period involves the mid-life and concluding years of operationof preponderant numbeys of the wellknown World War II standardized designvessels. Ce~tain of these types showedsome common inadequacies; others showedpropensities fortunately peculiar tothemselvesIn the early 1950,s the supertemk-ers of 2830,000 tons deadweight cameinto being, as did the llMarine~,,classof dry cargo carriers; subsequently, inthe early 1960,s, Illa~yof the U. S. sub-sidized oper-ators commenced laying upthe World War 11 types, and filled outtheir fleets with vessels specially de-signed for their specific trades, withmultiple units bein~ constructed from

the same design. Certain of these esSels suffered some of the weaknessespeculiar tc,the Wcrld War II designsNo sooner had the specialized drycargo essels been put together than thecontainer revolution came upon us , whichcreated considerable conversion inexisting ships and thinking. Als0, thehuge tanker revolution commenced afterthe mid-1950, s.With all of the changes, how muchrelay of operating exper-ience was ti-ans-fer~ed from one Erowth pattern to thenext concerning the faults of the var-ious types? What has been the cont~i-

bution of research and technology?This paper sets forth and treatswith, and in certain instances illustrates, specific inadequacies; it in-cludes observations on what has appearedto haw been inadequate communicationsi the past among the disciplines inVolved, makes reference to today, s cir,cumstaces, and makes some suggestionsfor the futui-erelating to technolo~y.

the sea rose up and smote the ship

CASUALTIES OF U. S FLAGwORLD WAR II BUILT VESSELSThe United States merchant marinefollowing Wo?ld War 11 was comprised oflarge numbers of a relatively small nunl-

ber of types of vessels, mostly builtduring the wa~, irlthe general cargo andtankship categories.Fron this circumstance common dis-orders were easily ascertainable, andvery definitely oftrepeated failuresshowed patterns not only for each typebut across the board fo~ all types insimilar trades , i.e. , all general cargoships, or all tankers.

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The types treated herein embrace steps taken (where applicable to pre-the Cl, C2, C3, Cti,Liberty, Victory, elude repetitive failure), are presentedand T2 Tanker. Certain of these types in the following, which by no meanswere designed prior to the U. S. entrY should be considered to be a completeinto World War II. and were a Dart of summarythe general rebui~tiing of the ti.S.merchant marine beginning in 1936.

Some of the problems peculiar tothe essels considered here, and thenecessary repairs and/or corrective

Failure of LongitudinalStYength MembersA common disorder was fracturing

of structural members contributing to

Fig. 1. Attempts by the crew to preent complete hull fracture

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Fig. 2. A complete longitudinal failure of a T2

longitudinal strength due to structural tanker.arrangement which caused local areas ofhigh ~tress. Structural arrangements such assquare hatch cutouts in deck platingFigure 1 shows emergency measures were eliminated by inserting radialtaken by the crew of a C3 type vessel shaped plates in the hatch corners (1)to prevent complete girth propagation Doublers were installed in way of squareOf a shell fracture, and FiguPe 2 house corners Discontinuities in lon-shows the complete failure of a T2 gitudinal members, such as resulted fromL-3

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the cutout for thein the bulwarks ofwere eliminated.accommodationthe lLibetytladdertype,

,rack ~rrestor,, straps were in-stalled on deck, gunwale, side shell,bilge shell, bottom shell, etc. , topreclude complete girth propagation offractures in deck and shell.

Ihmbably more than any other typeof damage the fracturing of structurecor,tributing to longitudinal strengthinfluenced the formation of the workinggroups, panels, and committees of theinteragency Ship Structure Committee,and the SNAME Hull Structure Committee.Doubtless the theatrical impact of thetypes of failures involved, particularlY where complete failure of the hullgirder occurred, often with loss oflife, had much to do with the emphasisplaced on seeking solutions to the Pro-blems, which, fortunately, were found.Pe,.ti,,entare (1) through (6) which arebut a rew of the pursuits stemming fromindividual efforts under the auspicesof SNAME, classification societies,etc., and in addition to which must beadded the staggering quantity of reports under the auspices of the ShipStructure Committee on works of uniqueQuality relating to establishment of

logitdirml and ti-ansverse forces, fastfractur~ am-est , computer programs, fullscale measurement programs, thermoplas-tic model studies, temperature influencestudies> etc. References (7) and (8)provide indices which include such worksemhi-acing 1946 to 1969.Relating to compressive stresses inthe bottom shell. and restricted to thetransversely fraked vessels, was the uP-ward buckling of the bottom shell be

tween transverse floors, largely withinthe midships half length, the phenomenoncomnmnlv called hin=intz. which was adirect ;esult of hog~in~ Lending mo-ments (In (1) the phenomenon istreated with respect to the Libertytype )The bottom shell in way of thehinging experienced a significantthinning in way of the unsupported spannominally midway between the transversefloors as contrasted with the thicknessof theshell immediately adjacent to thefloors (Invariably this factor was nottaken into consideration in presentingrecords of audigaugings or drillings to

establish bottom shell thickness es.)Figure 3 illustrates the hingingphenomenon

Fig. 3. Typical hinging damage

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The bottom shell plating requiredrenewal in the worst affected areas,and often the new plating showed thetYPical upward indentation betweenfloors, without significant thinning,after only a short period i service,perhaps because of the 10SS of resistante to compression from the neighboring plates which showed some hinging,but not considered sufficient to re-quire renewal when the new plating wasinstalled.

In a few instances intercostallongitudinal flat bar or inverted anglestringers were installed between transverse floors, breaking by perhaps one.third the transverse span between ex-isting longitudinal girders, in aneffort to put a stop to the phenomenon.The longitudinal stiffeners intercostalto the floors were of two arieties :one had ends fixed to the floors, Lheothe~ was cut ,hoyt of the flooi-s,being wholly supported by the shell immediately adjacent to the floo~s In afew rare instances the bottom of theintercostal members was sc~ibed and cutto fit the upset of the affected plates

It is no LewOrthy that as might be

expected longitudinally framed vessels,such as tankers, did not suffer thesickness.If a system of ti-ansverse frmnipgis to be utilized in the bottom of avessel it is obvious that the number oflon~itudinals , and/o~ the thickness ofthe bottom shell, within the midshipshalf len~th. must be Ei.Iemore consid-eration ~ha~ was the ;ase with the worldWaF II typesIt is also rathey obious that lon-

gitudinal framing in the bottom and deckof a essel (with t~ansverse f~aming forthe sides to reduce docking damage ) is amore efficient structur-al arrangementthan complete transverse framing.Slamming Damage

All the general ca~go types exceptthe Liberty type suffered indentationof forward bottom shell and buckling ofinternals , and in some cases secondarydamage to kingposts, piping, machinery,etc., from slanmig Figure 14il.lllstrates typical slamming damage to ~or,ward botLom shell pl.tin~.


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Little structural addition wasmade to reduce the frequency of thistype of damage.In one instance of damage, to aUCZ,,type vessel, high strength steel

was used to replace damaged shell plating on one side and the keel plating,while o~diary mild steel was utilizedto r-eplace damaged shell plating on theopposite side. After one year s oPeration the high strength steel was unaf-fected while the mild steel platingshowed severe damage; however, the areaof the VESSC1 in way of the slammingdamage was bodily set up 1% above thebase line. No repairs were made then,but a yea~ later, after two years Oper-ation subsequent to the installation ofthe high strength steel, again no dam-age was found to the high strengthsteel plating, but the damage to themild steel plating had been aggravated,and the bodily set-up had increased to2kJabove the base line.

FIJI-reasons unknown to the authorthis striking experiment was not madeknown to the technical f~aternity,which is unfortunate, fOP some extremely interesting aspects were a part anda result of the pursuit, not the leastof which was proof that to prevent indentation of shell plating from the in-fluence of slamming either the unsup-ported span should be reduced, or high

stren,qth shell plating can be utilizedwith the existing spans, keeping in mindthat the internals failed when the highstrength steel plating was used for thebottom shell with original internalspacing.As a matter of interest the recordsof the United States Salvage Associationshow practically no slamming damage onthe Liberty type (often forward-located hinging damage was confused with

slamming damage on tbe type)Additionally, tankers, includingthe T2 type, did not suffer from slam-ming damage, doubtless due to the factthat tankers can be ballasted down.An indication of the frequency, thelocation, and the cost of repairs ofslamming damage for the vessel types af-flicted is covered in (9). The damageinva~iably affected the keel strake, andstrakesA, B, C, and sometimes D, thedamage by no means bej.ng limited to theflat of the bottom. Local indentations

aS much as 4 were observed. Damage tointernals usually was not too severe,and where same occurred it generally~elated to buckling of the lower part ofthe transverse floors and the centervertical keel. Figure 5 illustrates theinternals of the vessel with the shelldamage shown in Figure b.

I

Fig, 5, Slamming damage (same ship as Fig. 4) showing minimal damage to internals

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.SNANIE, Slamming Panel was formedin the laLter 1950,s, and under its ~u5pices (10) was p~oduced, in which ase~ies of hull forms was presented ashopefully representative of forms whichwould develop relatively low slammingimpact pYessuI-es, this being achievedwith the one fullness so far investigated (11).In (17) there aFe p~esented ValeSto predict slamming imDact forces forvarious vessel for~bod~ transverse sec-tion shapes.Reference. (13), (14), and (15)

are simificant cont~ibutions of theShip S~ructure Committee to the pursuitof the subject of slarmning.A currently proposed pursuit unde~Ship Structure Committee auspices isdi~ected to the development of imstruments to measure, simultaneously, im-pact and ?elatie velocity of ship andwave. The program is aimed at correlat-ing forward bottom and bow flare impactpressures measured on ship and model,

and is fundamental to a bette~ understanding of the problems.Tanker InternalStructural FractuFes

The fracturing of the internalStructural members of tankers wa~ common. Such styucture rapidly revealsconfigurations and arrangements whichlead to fractures since corrosive attack is so standard in the tradeCo7rosion is accele~ated in areas ofhi~h stress, and such thardspotst werecommon in many of the internal struc-tural arrangements of World war IIvintage tankers Hard spots were foundi web frames, brackets joining transverse bulkheads to longitudinal structure, connections between transversebulkheads and longitudinal bulkheads,shell longitudinal stiffener penetra-tions through transverse bulkheads,tripping brackets, etcFluted transverse and longitudinalbulkheads showed a consistent propenSity to fyactuye in way of whe~e themetal had bee originally stressedbeyond the elastic limit to fcrm thecorrugations The circumstance becameparticularly eident whe~e adancedco~rosion obtained.Figures 6 and 7 present the structural arrangement of the 1T2,,tankez-.The fluted bulkheads and hard corneredconfigurations will be noted.Short of completely replacing thebulk of the internal arrangement whichled to fractures, the owners followedthe only course open to them, which wasto chip out and weld the fractures

(often also installing doublers in way) ,or to replace affected material withsound metal Access staging costs werealways a significant part of the ~epai~costs.In efforts to minimize recurrenceof fractures, where structure of simi-lar disposition and amangement wasreinstalled, replacing failed structure,some owners specially coated the structural internals in an attempt to prevent thinning; however, except in a fewisolated cases the internal coating oftankers did not really catch on untilthe new middlebodies ~ere fitted toWorld War II tankers.By the time the Jumbozing crazehit the U. S. merchant marine enoughhad been learned, and fortunately pas-sed on to most of the design fraternity,to inco~porate structural ai-rangementsother than those which had led to fail-ures in tbe first Dlace. One has onlvto look at cu~rentpractice in the de:sign and construction of t~anserseand longitudinal bulkhead arrangement ,

web frame am.angement , the methods ofeasement where flan~es and bulkheadsmake up to associat~d st~ctre, etc ,and compare it with the standa~d WorldWar II tanker str-ctural am-angement,to achieve m understanding of the reasons why f~actures were so commonplacei ,Worl~ War II tanker tonnage kee(16), (17), and (18).Figu?e 8 shows the marked changein struct?al arrangement for a rumbo,,z,,from original 11T2 ,arrangementTanke~ internal fractures arestill with us, but not at the rate ofthe 1940 s and 1950,s.

Side Shell DamageSide shell damage, consisting ofthe setting in of shell plating amd/orinternals , afflicted all types, pri-ma~ily f?om docking and from collisionwith lighte~s alongside. Little ornothing was done to design OF rebuildagainst it Structure was replaced asbefo~e. In many cases the damage wasin way of ref~igerated spaces and Fe-

quired most costly removals and re-placements to perform the ~epai~sFigures 9 and 10 a~e representa-

tive of typical side shell docking/Undocking damageDamage to Castings

Castings, employed on all of th,tYPeS, Presented an unpredictable ser-vice performance. This pronouncementstems from observation of the se ofsteel castings in serice for sternframes, shaft bossings and sleees,

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3 21

1[

2 3 4 5 6 7 8,-U

Fig. 6. II211structure (center tank)

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,

k------------------ J -------- .dFig. 8. Typical structure prOpOSed for Jumbo T2 (Ref. 16)

and a myriad of uses in the machinery riveted ship construction to achieve thecategory. compound shape forms for efficient hydrodmamlc flow.Few World War II vessel sternframes survived without showing frac-tures which required chipping out tosound metal. which often disclosedfurther imperfections such as shrinkagefractures, porosity, inclusions, etcSee Fi&ure 11.

Thermit welding, and Metalockwere , and still are, means of joiningfractured pieces of castings, and manyrepairs using these methods weFe madeto avoid the expense of the replacement .of an entire casting.When a major damage occurred (see Obviously the disadvantage of a

Figure 12) which required the replace- c~sting is that it does not lend itselfment of even a section of a cast steel to the cropping feature of welded shipstern frame, the repair cost was enor- construction.mous. One would ask then, why werecastings utilized in the ends of ships, ,,1bertyv Rudder Problemswhere the shell plating draws togetherand presents of itself massive strength? The Liberty contraguide ruddersPerhaps it was inertia, stemming from showed vulnerability to excess wear ofwooden and riveted steel construction, the wood bearing above the PuddeF, fFac-or at least a throwback to an era of ture of the rudder tube (stock), andpreweldment construction when castings fracturing of the rudder plating andwere the easiest method in i?on or steel welds in way of the division plate.L-10 -+

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Fig, 9. Typical side shell damage

Repairs consisted of replacing thewooden bearing with a bronze bearingarranged fo~ lubrication f~om the steer-ing flat, welding up orreplacement ofthe tube, and reinforcing the rudde~ inway of the division plate with anglesand strapsTailshaft Failures

The incidence of fractui-ing oftailshafts , either circumferentially,just aft of the liner. or in way of key-ways was alarmingly high foF ali typesof vessels See Figure 13.Where there was propeller dama~e iwas invariably alleged that a st~ikingCaus?d the f~actu~ing.Literally hundreds of metallur-gical examinations we~e made on behalf

of underwriters or,specimens of tail-sh;,fts taken from in way of the fractures, an?.many vayyin~ conclusionswere reached relating to the causes ofthe fractures Some concluded that Pro-peller impact led to the failures; how-ever, many concluded that fatigue wasthe prime causation, particularly inthe case of circumferential fracturesjust ahead of the propeller, indicativeof failure in cantilee~ed bending. Insome Tel,atiely rare cases the tailshaft material was founclto be atfault

In an attempt to reduce the recur-rence of fractures in way of keys thekeyway configuration was altered byspooning out and generously radiusingthe shaft material at the forward endof the keyway (Figure 14)?---

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Fig. 10. Typical side shell damage

Numerous repairs to shafts weremade by chipping or grinding away theshaft in way of fractures, and replacing the ~emoved metal with weld metal.Where the tailshaft was condemnedfor furthei-service, this invariably

led to the r-ewoodingof the top and bot-tom halves of the stern bearing to ac-commodate the diameter of the bronzeliner on the newly installed tailshaft

The Libertvl tailshaft n~oblem.which in many Ca;es Inolved khe com~plete fracture of the tailshaft just aftof the line~, and 10ES of propeller, wasfound to be related to a third oi-dertorsional vibration. critical at about78 RPM when the vesi+elswere light, andat about 70 RPM when loaded The USUal

cure was to install a propeller capableof absorbing normal full power at reduced RPM.Unfortunately, for all of thetypes considered here, in order to r-e-move the propeller for even the simpleexamination of the tapered end of the

tailshaft, it was necessary to with-draw the tailshaft into the vessel, amost Iaborous and expensive procedure,and further, if it was necessary toremove the tailshaft from the vessel,it was generally found less expensiveto make an opening in either the shaftalley or the shell to accommodate thisremoval rather than to attempt to movethe tailshaft Into the engine roomspaces and out through the fidley. SeeFigures 15 and 16.

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Fig. 11. Typical fracture in cast steel stern i-pame

Had the designers of these vesselsbeen aware of the tailahaft problemswhich arose they most certainly wouldhave arranged the Vessels such that atleast the propellers could hawe been I.e.moved without drawing the tail,shaft inboard.Today we find many vessels which

can accomplish the immediate abowe, andalso we aye blessed with the developmentof a satisfactory seal allowing for oillubricated stern bearings which void thenecessity of a bronze liner; some of thearrangements een allow for inspectionof th~ tailshaft forward of thepropel-ler, afloat.We are also blessed with the de-velopmenthydraulic

time consuming and difficult procedureswhich were a part of the propeller andtailsbaft problems of World War IIstern gear arrangement.Stern gear arrangement is as much

a Part Of the naval architecture/strength of materials discipline as themarine engineering discipline, and itis mentioned here for obvious reasonsTailShaft Liner Erosion

A phenomenon which showed up withno regularity, and appeared to affectonly a few of the vessels here treated,of all types, was tbe appearance oflongitudinal bands of erosion on tail-shaft liners . radially located nominallyof the ,,pilgrimptnut and other between prophller bla;es.arrangements which amid the LL-13


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Fig. 12. Major damage requiring replacement of much of a cast steel stern frame

Many theses were advanced to ra-tionalize the existence of these bandsof erosion, ranging from water pulsations through the bearing, eleCtTOIYSi Staking place from generated staticelectricity or galvanic action, etc.In one instance it was even allegedthat the damage was caused by the vessel lying in contaminated waters.

It is believed that to this day nopositive knowledge is at hand as to whythe phenomenon occurred; however, theneed to establish the true cause hasbeen obliterated by the development ofthe sealed, oil lubricated stern bear-ing, which fortunately shows no vulner

ability to such damage.COMPHJNICATIONS BEFORE, DURING ,AND AFTER WORLD WAR II

Surely neither the designers northe builders of the World War II typeswere aware that they were building inweaknesses.Further to the foregoing, and onthe subjects of slamming damage andhinging damage, both types of damageusually lent themselves to long periodsof deferment of repairs, and also thedamage was not of a theatrical natureand invariably was not accompanied by

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Fig. 13. TYPtcal tailshaft fractures, both circumferentially and in way of keyway

10ss of life, all of which simply dldnot lead to a broad awareness of thefrequency of the damage among the designfraternity. Further, the standard bam-boo curtain which seems to exist be-tween field personnel and design personnel was apparentIn large measure the owners didnothing about the types of damage whichoccurred except to make repairs in kind,or at best respond to classificationrecommendations. The very nature ofowning one of a vast group of similarships simply did not lend itself tounique or individual thinking. Eventhough few owners were making plans for

new construction, most owners consider-ed the World Waz.II vessels as obsoleteand not worthy of grandiose, expensiveschemes to reduce recurrences of thetypes of diseases that the owners knewthey were susceptible to. Under thecircumstances it is perhaps remarkablethat certain owners, who made it theirbusiness to maintain a rapport withSNAME, caused pursuits to come into be-ing which in the long term did lead tosolutions; bowever, it is clear thatsegments of the ship designing fratern-ity had no feedback concerning certainof the experience even after years ofoperation and failures, and it was evident that there was a gap in the flow

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Fig. 14. Typical tailshaft fractures (shows spooned keyway)

of communications between the repair di-visions and the design divisions ofmost shipyards. It was also apparentthat a means was missing to create aflow of information between seagoingpeople and their own,:rs, and a continuation of this flow from owners to thosein the shipbuildin& ad ship designfraternity.

One might be curious as to howmuch of the oft-repeated s,tandardweaknesses, shown across the board byso many of the World War II built/

designed vessels, could have been avoided by better communication; however, inpursuing this we should keep in mindthat the U. S. merchant marine jumpedfrom Wo~ld War I to World War II largelywithout any new construction or design,and it is remarkable that the flaws wereas few as thev were. Additionally. thestate of the irt of the welded shiiwasin its infancy just prior to 1940.

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Rig. 16. Shell plate opening made in order to remove tailshaft

a propensity to fracture, raisin~ questi3ns as to whether or not thepe hadexisted a proper rapport between shipyard repair and design divisions someof these fractures related to the cOntinued use of corrugated bulkheads inlieu of flat plate stiffened with weldedstructural shapes.Ship designers 2nd builders world-wlde were feelinz their way with tankerinternal structural configurations whichwould not fracture in service, and it is

under stamiable that certain of the con-figurations simply did not stand up.One such configuration, once again Proving that stretched metal such as resultsf~om corrugations or joggles does notstand up, ~elated to horizontal tiebeams (struts) supportin~ the inboardand outboard Dortions of the web frames.~nd the webs ;f horizontal bulkheadstiffeners in the wing tanks of a classof tankers Figure 19 illust~atcs thelocation of fractures, and aiso themethod of altering the structure to

avofd fracture.? in the future , which wasapplied in each wing tank of every ves-sel built with the original construction.

Another circumstance concerningtanke~ structural configuration very vul-nerable to fracture, and related to thefairly ~ecent concept of segregated cleansalt wate~ ballast spaces, is illustratedin Figure 20, which is a sketch of atransverse web frame in way of the cut-outs accommodating tbe longitudinal stif-fener-s of the longitudinal bulkheads inthe clean salt water ballast tanks, thestructme being uncoated. Thinning ofthe structure in way of the fracturesshown was down to almost zero thicknessafter less than two years service, frOMoriginal nominal 1/2 thickness, whichthickness still nominally obtained inareas of low stress

The failure was a direct result ofstress set up by fluids on one side of abulkhead only, and resultant accelerated --

.

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,,I

Fig. 17. Slamlng damage to a post World War 11 U.S. fla~ vessel

corrosion and loss of strength in areasof hip,hstress, causing the metal tofail in shear in way of the cutouts.While the cutout configuration fo~ thebulkhead longitudinal swas the same inthe cargo wing tanks, and the webframes in those tanks were also un.coated, Lhe massively accelerated thinning had not occurred, and no fracturesas yet obtained, obviously due to theProtection against corrosion by thecargo oil.

In the segre~ated clean salt waterballast tanks there was no Fecourse butto crop out and replace affected metal,installing closure pieces in way of thecutouts to help absorb the shear, andCl?an the webs f~om top to bottom, andcoat same.

The pe~formance of the huge tank-ers bore ot the fact that great emphasis had been laid on longitudinalstrength, for there were little or nolongitudinal strength problems in theiroperation, but this was not the casewith transverse structure. Cripplingof huge webs occurred in the early

VLCC s , which requirecl that greate~ at-tention be gien to eFtical stiffenersand their spacing (19)

Problem. relatin= to damaee to tbeforecastle head and f;rward up?er shellplating of the larger tankers, fro ntheeffects of the sea, began to show upeven on the 2830,000 tons deadweighttankers wbicb appeared in the ea~ly1950s. The damage related to the set-ting down of forecastle deck plating(see Figure 21), crippling of webs andstanchions (see Figur-e 22), generallyaccompanied with the Settinx in of theupper flared section of the-essel atthe sides of the forecastle head, andupon occasion the indentation of the upper stem and forward side shell platingand supportin~ structure (see Figure 23)The damage as a type led to a revampingof classification structu~al criteriafor forecastle head design; cur~entlythe affliction appears less frequently.The fact that the navigating bridge wasmoved all the way aft probably had someinfluence on the frequency of occurrenceof this type of damage, since those inthe wheelhouse were so remote from tbe

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Fig, 18. Slamming damage (same ship shown in Fig. 17) showing damage to internals

area of damage, and inadvertently theymay have driven the vessels of this verylarge displacement type too hard intothe seaways.A type of damage which seems toconsistently camy on, and which af-flicts all types of vessels (which canbe disastrous when it occurs to tanksformed by the vessels hull, such as isthe case with bulk liquid carriers) , isthe rupturing of tanks of vessels duringthe filling of these tanks with fluidsThe fact that the damage occurs 80 oftenwould indicate that few people are awareof how important it is to arrange tank

ventindoverflow systems to Drevent thedamage: which is invariably iaid at thedoor of crew negligence. In some casesblanks or valves have been installed inan otherwise adequate venting system, toprevent overflow of oil or other contaminating substance into the water surrounding the vessel. In some casesflame screens in vents have been paintednearly shut In some cases the heightof the vent head is such that fromstatic forces alone there is sufficienthydrostatic pressure built up to severely

damage a vessel?s tanks. Reference (20)indicates that it is not alwaYs suffi-cient to proide a crosssectional overflow pipe area 1.25 times the fillingpipe cross-sectional area, it sometimesbeing necessary to make the ratio ashigh as 1:4 to allow for constraints inthe overflow pipe.

Concerning steel castings, a remarkable circumstance occurred, from thestandpoint of tim?ng, for during a fourmonths period, approximately five yearsafter delivery of the vessels, four cast~tee~ IIMaPInerII rudde~ horns evidencedsmface fractures which required massivechipping out and welding up of fractur-es, and in some cases the renewal of theentire rudder horn casting. The diseaseseemed to be on one side of the castings,and was in large measure laid to therising to the surface of slag and inclu-sions on the affected side of these largecastings which were poured on their side.See Figure 24.

Propellers of nonferrous cast ma-terials were not Without their problems,particularly those of special alloys of

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~ .l.b--~ lL===-

J-i+ * DAT\ L JOGCLED CONNECTION(COPVED J+*GL?SPLACSDWITH )U3ECT VKL3 FI-A7E)

Fig. 19.Fractures in way of joggles of tankerweb frame tie beams and bulkheadstringers, and alterations to avoidfuture failures

alleged high strength. While a couponof the original parent material may haveshown an ultimate strength of, say,98,000 pounds per square inch, and thepropeller blade thickness was determinedon this basis. after failure of theblade in bend;ng, in service, a coupontaken in way of tbe failure submittedfor metallurgical examination in manyinstances sh;wed an ultimate strength ofapproximately 40,000 pounds per squareinch; clearly a case of a change in thephysical characteristics of an alloyperhaps resulting during the heating orthe pour of the propeller casting fromthe original billet(s) See Figure 25.

In another area, side shell damagewent marching forward, particularly forthose vessels laid out in the tradition-al fashion to accommodate mooring. Theresults in the St. Lawrence/Great LakesSeaway were disastrous, and caused cer-tain salt water U. S. flag operators tovow they would abandon such service for-ever. This was a direct result of thelack of rapport between the salt waterand Great Lakes Segments of the U. S.merchant marine. The missing equipmenton the salt water vessels was wire moor-ing winches , universal chocks, sternanchors, and the lack of tumble home andTubbing strakes on the sides. The re-sulting side shell damage during locktransiting was enormous, as was bottomand stern gear damage from grounding aftwhen ancho~ed by one anchor at the bowin narrow estuaries (the docks beingengaged by other vessels waiting totransit the locks) The lack of theproper ship handling equipment literallydrove the salt water vessels of the dayout of the Seaway, and while most of theU. S. vessels never returned to the Sea-way (certainly for many reasons) , iron-ically the Great Lakes wire mooring ar-rangement has caught on, largely stem-ming from the necessity of such equip-ment on the larger seagoing bulk caP-riers which could not be handled PPO -perly with a multitude of fiber lines,revolving gypsy heads, line stoppers,and the quantity of personnel requiredto operate such archaic equipment.SAFETY, COMMUNICATIONS , AND RESEARCH

What is safety worth? Who benefitsfrom a safe ship? Who is in a positionto promote safety tbe most?If everything rotates around lowcost of transportation, which taken toits extremes means that each vessel willincorporate only minimum requirements,how can damage-conscious operating per-sonnel prevail? Must an owner be forcedby monetary reasons to limit his shippurchases to standard production itemswhich can be produced with the minimumdollar?Taking the example of LNG vessels ,current predominant fashion is to placeone-fifth or one-sixth of the totalcargo in tanks of one shape or another. .It is apparently left to chance to de-termine whether or not the product

should be carried in many more contain-ers. In this case design agents arecurrently in no position whatever tosustain an argument to depart from whatis accepted as conventional arrangement,from the standpoint of added safety (andits cost),versus what is saved in theend through that added safety.The public, shipowners, financiers,and underwriters of every category all-. .,.can benerit mom extra salecy arrange-

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LFig. 20.Fractures in way of web framecutouts in segregated cleansalt water ballast tanks

ments, particularly with vessels carry-ing a product which has huge potentialto damage life and property, yet thereis currently no way of placing a dollarvalue , at the time of ship design orconstruction. on the incorporation ofsafer arrangements in a vessel to carrysuch cargoes It is unfortunate thatthe basis for safety always seems to beregulation after the fact

In treatin= with less dramatic cas-ualties that pr~bably will never lead toregulation, it becomes obvious that shipdesigners are in no position to developimprovements, or suggest the incorporation of features which cost money, wherethey have no statistics on damage exper-

ience relatin~ to what might be avoidedif the improvements or features were in-stalled. For example, without statis-tics relating to the prevalence and costof side 6hell damage from mooring, oneis in a poor position to recommend theinstallation of a bow thruster.As another example, it Is submittedthat design agents are not in a positionto place more emphasis on vent arrange-

ments of tanks than has been customaryin the past How much information onthe bursting of tanks through allegedcrew negligence has been processedthrough design offices? The damage isprevalent, and can cost hundreds ofthousands of dollars to repair.It is submitted that the design de-partment of a shipyard is in a very poorposition to determine whether or not araised forecastle should be installed ona ULCC, with the attendant additionalcost of same, versus a flush deck ar-rangement, when there is little or nofeedback from seagoing personnel, oxoperators, condoning or condemning theflush deck arrangement on a typical ves-sel of the type.Traditionally ships have not beenlaid out to make it easv for othe~s torecord damage; for exam~le, it is seldomspecified that frame numbers be locatedon vessels. Whose fault is this? Howmany owners reauire that a casualty bookbe ~aintained in each ship, to avo~dwading through log hooks to find in-stances of casualties or records of same?Some essel operators are in a pos-ition to frequently add new vessels of.their own design to their fleet Such

fortunate operators can be guided by thefaults of vessels which they built ayear or so previously. Presuming goodin-house communications, a very highlevel of operating efficiency, by selec-tivity, can result with such an arrange-ment. Such an organization is in a POs-ition to contribute much to researchcarried out under public auspices, andimportantly, is in a position to knowwhat needs to be researched.Where an owner operates with shipsdeveloped by others, whether they bestandard designs of shipyards, or gov- -ernment sponsored designs, the liklihoodof that operator contributing to research,

via the experience of his own personnel, ;would seem to be low, for his personnelsimply will not have the keenness of pur-suit in establishing how their designcan be made better, for it was ot their 1design in the first place.Whatever the cause, where an opera-tor?5 personnel more or less take a backseat to the subject of research, researchis forced into the academic theater. I

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Fig. 21. LaFge tankey I_oi-ecastlc head damage showing set-down of deck

Reference (21) ~i-ovides a SUmmarVof sources of person;el and ship casu~lty data, and it can be concluded fromthat work that very little organized er,phasis has been placed on the gatheringof such data. Full ship damage data reQuires knowledge of not only what wasdamaged, how often it was damaged, andhow it was damaged, but also the cost ofrepairs The cost input certainlyshould be a nrimc catalvst to look intovarious fail;res, but h;w oft, ii re-search based on such input? References(22) and (23) are two of the few effortsexistent in the casualty gatheringtheater.

Certainly a significant part of I-esearch ?elates to the establishment andmaintenance of a system to gather damagestatistics, for without a specific indi-cation of the t~ends and patterns ofdamages the leads to research aye of ahaphazard nature. When flaws or fail-ures are &ien a specific dollar value,research will trend more to be on apractical basis, as opposed to a theoretical exercise perhaps dedicated tolong-term results.

When one considers the willingnes~of owners to Jump inlx a~eas haing].ittleor no Operzting history, one mustconcede that the owners hae shown either massie fortitude Ifibeifigwillingto take what most cautious people wouldconsider prohibit i.?erisks, or havemov?d forward in blessed ignorance Inall but a very few instances things haeworked ot pretty well fo~ such risktakers Undoubtedly reseamh in metal-lurgy, stru.tmal analysis , and weldinghas made the record possible.SUGGESTIONS FOR THE FUTURE

Quite apart from the specific in-stances mentioned earlie~ heyein of apparent communications problems betweenthe disciplines inolved, there is ademonstrated current need for operational damage statistics, and the pOSsible sources of sam. Time and again,to justify (or een establish) programs,agencies and contractors (particularlythose representing d~sciplines periph-eral to the marine theater) demonstratetheir need for statistics, Time consum-ing education best desc~ibes the circum &-L-23


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compensation foy making his vessel a,a::-able for instrumentation.

Fig. 23.Huge tanker, showing buckling ofinternal structure underdeck forward

rapport which, among ccFtain of the disciplines, is now totally missing, andhopefully, remedies for the ills wouldgrow out of such distribution.

,Morecandor is needed from allsides, and more cooperation. C1assification societies are in a unique positlon to accumulate information on thoseparts of vessels which are repetitivelyadersely affected either by the forcesof nature or by people; their standardswill not be changed where they needchange without a candid disclosure offaults.Where research programs are put to-gether and funded, which include instru-mentation of vessels, largely to providelong-term benefits, and the programs relate to new and unusual vessels, it isobvious that a part of the fundingcould well be dedicated to the solutionof problems that were not anticipatedbut which when they occur require immed-iate solution. In this fashion an ownerwould achieve a measure of immediate

Stern gear ibration probl?,,,, ::1-cludlng bearin,5/shaft fallmes and losso? propel I.ers,hae sppeamed i.nthe Iel-e.tiely high speed, cry high poweredfine lined vessels of this modern age.On the othcy end of the fullness spec-trum. ibi-ation hss Dlaxued full shi~sfor years, and it wiil ;? of immenseimportance to assess its probability inthe proposed low L/B, high B/H very fullvessels crFenL1. being considered, Re ferences ( ?4)through 31 lay emphasiso the importance of the vibration pro-blem.

The traditional handling of pFopulsion systems leads to fractional izationof disciplines. Many of the problems aFcof a ibratory origin stemming from pFopcllerinduced ibration (hydrodynamics)and the reaction of tbe hull (structuresand mechanics) Obiously there is awhole missing link treating totally withthe hydrodynamics of the waterflow intothe propeller, the propeller-induced Pul-sations, and the resnonse of the hullgirder. To date, vibration analysesseem to be made by necbanically andstructurally oriented people, botb ofwhom come j.ntothe F>icture after hydrodynamically oriented persons hae fin-ished their pursuits In many casesthis leads to disastrous results,

Systems must be put together topredict vibration problems with models.This may require accommodation for mo-tion in the model, s propulsion system,including shafting, struts, bearings,etc , with instrumentation to measurewhipping or rnocment in shafting andshaft beaFings, and possibly actualstmcture simulation in tbe models, per-haps using holographic methods as de-scribed ir,References (32) and 33 .

In the area of wave forces the worldawaits the development of a blanket, formodel scale use, and full size use, whichcan be placed upon a shipvs shell thatwill recoi-dnot onl ?Dressures . but tbeenvelopes of pressu;e~ from wa;e slapand slammin 3.Theye is an interagency Ship Structure Committee WheFe are the inter-agency Ship Machinery Committee and .SbipOperations Committee, the latter treatingwith the human error aspect of bull andmachinery pFoblems?While there may be currently somemoves to the contrary, traditionally,wouldbe naval architects, when they goto sea, end up in the engine room. Ac-cordingly, they do not personally exper-ience the problems of deck operation.They aFe in no position to treat withthe layout of cargo handling equipment,moorin~ equipment , anchoring equipment ,

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Fig. 24. Cast steel Mariner rudder ho~n showing metal removal in way of fractures

etc. Undoubtedly this was one of the CONCLUSIONSreasons why UP to the end of World WarII deck personnel were toppin~ cargo 1.b~oms with a cargo winch and stoppingoff topping lift wi?es with chain stoppers. Perhaps this is also the Feasonwhy salt water vessels are een todayfitted with the outlandish ar~angementfoT moorin~: which i.?obtained with fiberlines, in ?ieu of wire mooring winches 2,34 The placing of expensie machin-ery such as an anchor windlass abowthe deck, exposed to the weather is adi~ect result of people in one d~scipline either not paying attention to theproblems of another discipline, or notgiving thought as to how circumstancescan be bettered. 3.

4.

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TheFe were inhe~ent weaknesses deSimed and built into the multi~leun~ts of a relatively few typesofvessels making up the U. S. merchantrm~ine, immediately prior to andduring World War II.In some areas attention was given tothe weaknesses and cures were found.GeneTF.lly theFe was a demonstratedlack of communications between thosewho knew of the weaknesses and/orvlnerabilities , and those designingnew vessels.CeFtain of the inherent weaknessesappeared in post World wa~ II ve8sels of the U, S. merchant marine.Ship damage history should lead toresearch currently this is seldomthe fact in the United States

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Fig. 25. Section of p~opelle~ blade in way of f~acture

5.

6.

7.

8.

9.

The development of a system for thegathering of vessel casualty data,definitely Including the nontheatrical but often-repeated typesof damages, lies dormant There isa need for the results, and the effort should be pursued vigorously.All pertinent disciplines should reCeive the Iesults of 5, and shouldoccasionally meet to better alignthe solution of problems as they aredetermined.Means to predict vibration p~oblemsIn the model stage must be implemented, and the need cannot be toost~ongly emphasized.An interagency Ship MachineFy Committee and Ship Operations Committeeshould be brought into exist?nce.Emphasis should be placed on thenecessit Y of deck de~artment serviceas a pari of naval architecturaltraining.

L-

ACKNO,WLEDCMENTThe type of darage information ineluded herein is represents-;ive of thedailv effort of :he United States Sal-vageAssociation which orgar.ization basnever failed to generously release itsfindings to those interested in betterin~ eSSeI operational efficiency.Special appreciation is also extended LO >1T8.Plur~el Fox who so patientlY and carefully co?mitted to paper themany wo~ds makin~, up this effo~t

REFERENCES1. ,T.Vasta, Structural Tests on theLibe~ty Ship S,S. Philip Schuyler,- SNAME, 19072. M. Lotveit, C. Murer, B. Vedeler,H. Christensen, WOVe Loads on a T-2Tankey [dodel, Publication No. 18,Det Norske Veritas , February, 19613. Georg Vedeler, Speed and strength ofLaFge Tank.?., Publication No. 21,

Det Norske Verita. , May, 1961

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5.

6.

7.

8.

9.

10.

11.

12.

13.

14,

15.

16

17

;eorg Vedeler, TO What Extent doBrittle Fr-.zctureand Fatigue Inter-est Shipbuilders Today?, PublicationNo. 32, Det Norske Veritas, August,1962R. Faresi, A Simplified ApproximateMethod to Calaulate Shear Force andBending Moment in StiLl Water at AnyPoint of the Ship s Length, Publication of American Bureau of Shipping,April, 1965E. G. U. Band, Analysis of Ship Datato Predict Long-TervnTrends of HullBe-ding Moments, Publication ofAmerican Bureau of Shipping, Novem-ber, 1966Index of Ship Structure CommitteePublications (1946 - April, 1965)Ixdez of Ship Structure CommitteeRapor.ts, SSC Report No. 200, Jan-uary, 1969H. S. Townsend, Some Observations onthe Shape of Ship Forebodes withRelation to Heauu Weather, N. Y.Metropolitan Section Paper, SNAME,1960H. S. Townsend, A Se?ies of Cargovessel Hull FOFWIS, T&R Symposium,SNAME, 1967M. K. Ochi, Pe?fozvnance of Tuo HullFoFma (U and V) in IYrwgu LaP Wczues,T&R Symposium, SNAME, 1967M. K. Ochl and L. E, Motter, Predie -tioriof Slamming Chaz.acteristics andHull Responses for Ship Design,_ SNAME, 1973J. R. Henry and F. C. Bailey, SLam-rningof Ships: A Critical Revieti ofthe Current State of Xnotiledge, SSCReport No. 208, 1970J. W. Wheat on, C. H. Kane, P. T.Diamant, F. C. Bailey, Analysis ofSlamming Data f?mn the S.S. Wo2ue?-i.e State, SSC Report No. 210, 1970P. Kaplan and T. P. Sargent, FurtherStudies of Computer Simulation ofS1.mmin,gand Other Waue-Induced Vi-brwtory Structural Loadings on Shipsin Vavee, SSC Report No. Z31, 1972M. Maek Earle, The what, why, Hou ofa Jumbo T-2> ~ Engineering/Log,April, 1.956A. Haaland, Damages to ImportantStructural Parts of the 8.11,European Shipbuilding, No. 6, 1967

1.8.

19.

20

21

22

23

24

25

26

27

28

29

30

31

R. S. Little and S. G. Stiansen,Cor.reZation of Full-Scale Experi-mental and Computed Stresses ofMoin supporting Structure on LargeTanke?s. Paner oresented beforeAmerican Peirol~um Institute Con-ference, May, 1971H. A. Schade, Interpretations of the,E~So,VOFUayf,Static Test6, ~SNAME> 1973Germanischer Lloyd, Unintended Pres-su?e Inc~ense During Filling of Bal-last Tcnks, 8th Shipbuilding ColloquyShipbuilding Industry, - und-, No. 8, Vol. 23, 1971 Panel on Merchant Marine CasualtyData, Mervhant Marine CasuaLty Data,Prepared under auspices of MaritimeTransportation Research Board,National Research Council, NationalAcademy of Sciences , July, 1973C. J. Hamrin and H. S. Townsend,Ship Damage, Marine Engineering/Log,October, 1963- appeared inFaii-play, 28 May, 1964; The ship-builder ~ Marine Engine-Builder,November, 19nropean Shipbuild-~, NO. 6, 1963; and =Q=, January, 1964)S. Hawkins , G. H. Levine, R. Taggart ,A Limited Survey of Ship structuralDamage, SSC Report No. 220, 1971F. H. Todd, Ship null Vibration,First edition, London, Edward Arnold(Publishers) Ltd. , 1961Editorial, After.body Vibrations inLnrge Ships, European Sbipbuildlng, ;No. 6, 1967A. C. Viner, Ship Vibration, Lloyds ~Register of Shipping Report No. 53,1968Editorial , Joint Efforts for Mini- 1mizing Engine czndP?opeller InducedVibrations, European Shipbuildi~, jNo, 5, 1970

IT. Sontvedt, P~opelle?r.Induced Ezi-tation Forces, European Shipbuilding,No. 3, 1971E. F. Noonan, Design Considezvztionsfor Shipboard Vibration, = iTechnology, SNAME, JanuarY, 1971 [F. E. Reed, The Design of Ships toAvoid PropeZler-Induced Vibrations,= SNAME, 1971w. s. Vorus, A Method for Analy.in?the Prope LLer-Induced VibratoryForces Acting on the Surface of aShip stern, ~ SNAME, 1970

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32 B. S. Hockley, Measurement of Vi-bration by HoZogrwphg, ~ TheInstitute of Marine Engineers,Vol. 84, Part 6, 197233. H. A. Peterson and J. P. Sikora,Ann Z~8is of Plastic Models of ShipStructures Using RoZogrcphy andStrain Gauges, NSRDC Report 4517,

February, 1975

34. H. S. Townsend, The Case for WireMoo?ing Winche8 Marine News,April, 1950

75symp12_observation of ship damage over the past quarter century

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