75Symp12.Pdf

,$..,WC,, THE SOCIETYOF NAVAL ARCHITECTSANO MARINE ENGINEERS 74 Tr,nityPlace,New York,N.Y.,10006 ,+’ *% Papert. he presentedatme Sh’pSt,.ct”,esyrnpxl.m 8 ~e Wmhi”@on,D.C.,October6.3 1975 c+, (ii ? o% ,~“,,*,.+. Observation of Ship Damage over the Past Quarter Century H. S. Townsend, Member, United States Salvage Association, Inc., New York, N.Y, 6>COPY@ht 1975 byTheSociety.fNavalAmh(tectsandM..,..Engineers ABSTRACT This paper treats with ship damages taken fyom surveys of the United States Salvage Association, In. ., over the past quarter century, on vessels of all flags. Insofar as U. S. flag vessels are concerned, the period involves the mid- life and concluding years of operation of preponderant numbeys of the well– known World War II standardized design vessels. Ce~tain of these types showed some common inadequacies; others showed propensities fortunately peculiar to themselves In the early 1950, s the supertemk- ers of 28–30,000 tons deadweight came into being, as did the llMarine~,,class of dry cargo carriers; subsequently, in the early 1960, s, Illa~yof the U. S. sub- sidized oper-ators commenced laying up the World War 11 types, and filled out their fleets with vessels specially designed for their specific trades, with multiple units bein~ constructed from the same design. Certain of these “es– Sels suffered some of the weaknesses peculiar tc,the Wcrld War II designs No sooner had the specialized dry cargo “essels been put together than the container revolution came upon us , which created considerable conversion in existing ships and thinking. Als0, the the sea rose up and smote the ship huge tanker revolution commenced after’ the mid-1950, s. CASUALTIES OF U. S FLAG With all of the changes, how much wORLD WAR II BUILT VESSELS relay of operating exper-ience was ti-ans- fer~ed from one Erowth pattern to the The United States merchant marine next concerning the faults of the var- following Wo?ld War 11 was comprised of ious types? What has been the cont~i - large numbers of a relatively small nunl- bution of research and technology? ber of types of vessels, mostly built during the wa~, irlthe general cargo and This paper sets forth and treats tank–ship categories. with , and in certain instances illus– trates, specific inadequacies; it in- Fron this circumstance common dis- cludes observations on what has appeared orders were easily ascertainable, and to haw been inadequate communications very definitely oft–repeated failures i“ the past among the disciplines in– showed patterns not only for each type Volved, makes reference to today, s cir– but across the board fo~ all types in ,cumsta”ces, and makes some suggestions similar’ trades , i.e. , all general cargo for the futui-e relating to technolo~y. ships, or all tankers. !,-1 The types treated herein embrace steps taken (where applicable to pre - the Cl, C2, C3, Cti, Liberty, Victory, elude repetitive failure), are presented and T2 Tanker. Certain of these types in the following, which by no means were designed prior to the U. S. entrY should be considered to be a complete into World War II. and were a Dart of summary the general rebui~tiing of the ti.S. merchant marine beginning in 1936. Failure of Longitudinal StYength Members Some of the problems peculiar to the “essels considered here, and the A common disorder was fracturing necessary repairs and/or corrective of structural members contributing to Fig. 1. Attempts by the crew to pre”ent complete hull fracture L-2 + Fig. 2. A complete longitudinal failure of a “T2” longitudinal strength due to structural tanker. arrangement which caused local areas of high ~tress. Structural arrangements such as square hatch cutouts in deck plating Figure 1 shows emergency measures were eliminated by inserting radial taken 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 square Of a shell fracture, and FiguPe 2 house corners Discontinuities in lon- shows the complete failure of a “T2” gitudinal members, such as resulted from L-3 !--- the cutout for the accommodation ladder lo”git”dirml and ti-ansverse forces, fast in the bulwarks of the l’LibeTty ’ttype, fractur~ am-est , computer programs, full were eliminated. scale measurement programs, thermoplas- tic model studies, temperature influence !,Crack ~rrestor,, straps were in- studies> etc. References (7) and (8) stalled on deck, gunwale, side shell, provide indices which include such works bilge shell, bottom shell, etc. , to emhi-acing 1946 to 1969. preclude complete girth propagation of fractures in deck and shell. Relating to compressive stresses in the bottom shell. and restricted to the Ihmbably more than any other type transversely fraked vessels, was the uP- of damage the fracturing of structure ward buckling of the bottom shell be– cor,tributing to longitudinal strength tween transverse floors, largely within influenced the formation of the working the midships half length, the phenomenon groups, panels, and committees of the comnmnlv called “hin=intz”. which was a interagency Ship Structure Committee, direct ;esult of hog~in~ Lending mo- and the SNAME Hull Structure Committee. ments (In (1) the phenomenon is Doubtless the theatrical impact of the treated with respect to the “Liberty” types of failures involved, particular– type ) lY where complete failure of the hull girder occurred, often with loss of The bottom shell in way of the life, had much to do with the emphasis ‘hinging” experienced a significant placed on seeking solutions to the Pro- thinning in way of the unsupported span blems, which, fortunately, were found. nominally midway between the transverse Pe,.ti,,ent are (1) through (6) which are floors as contrasted with the thickness but a rew of the pursuits stemming from of the’ shell immediately adjacent to the individual efforts under the auspices floors (Invariably this factor was not of SNAME, classification societies, taken into consideration in presenting etc. , and in addition to which must be records of audigaugings or drill ings to added the staggering quantity of re– establish bottom shell thickness es.) ports under the auspices of the Ship Figure 3 illustrates the “hinging” Structure Committee on works of unique phenomenon Quality relating to establishment of Fig. 3. Typical hinging damage L-4 . The bottom shell plating required expected longitudinally framed vessels, renewal in the worst affected areas, such as tankers, did not suffer the and often the new plating showed the sickness. tYPical upward indentation between floors, without significant thinning, If a system of ti-ansverse frmnipg after only a short period i“ service, is to be utilized in the bottom of a perhaps because of the 10SS of resist– vessel it is obvious that the number of ante to compression from the neighbor– lon~itudinals , and/o~ the thickness of ing plates which showed some hinging, the bottom shell, within the midships but not considered sufficient to re- half len~th. must be Ei.Ie” more consid - quire renewal when the new plating was eration ~ha~ was the ;ase with the world installed. WaF II types In a few instances intercostal It is also rathey ob”ious that lon- longitudinal flat bar or inverted angle gitudinal framing in the bottom and deck stringers were installed between trans– of a “essel (with t~ansverse f~aming for verse floors, breaking by perhaps one. the sides to reduce docking damage ) is a third the transverse span between ex- more efficient structur-al arrangement isting longitudinal girders, in an than complete transverse framing. effort to put a stop to the phenomenon. The longitudinal stiffeners intercostal Slamming Damage to the floors were of two “arieties : one had ends fixed to the floors, Lhe All the general ca~go types except othe~ was cut ,hoyt of the flooi-s, be– the “Liberty “ type suffered indentation ing wholly supported by the shell im– of forward bottom shell and buckling of mediately adjacent to the floo~s In a internals , and in some cases secondary few rare instances the bottom of the damage to kingposts, piping, machinery, intercostal members was sc~ibed and cut etc. , from slanmi”g Figure 14il.llls- to fit the upset of the affected plates trates typical slamming damage to ~or– ,ward bot Lom shell pl.atin~. It is no LewOrthy that as might be ● Little structural addition was stren,qth shell plating can be utilized made to reduce the frequency of this with the existing spans, keeping in mind type of damage. that the internals failed when the high strength steel plating was used for the In one instance of damage, to a bottom shell with or’iginal internal UCZ,,type vessel, high strength steel spacing. was used to replace damaged shell plat– ing on one side and the keel plating, As a matter of interest the records while o~di”ary mild steel was utilized of the United States Salvage Association to r-eplace damaged shell plating on the show practically no slamming damage on opposite side. After one year! s oPera– the “Liberty” type (often forward- tion the high strength steel was unaf- located hinging damage was confused with fected while the mild steel plating slamming damage on tbe type) showed severe damage; however, the area of the VESSC1 in way of the slamming Additionally, tankers, including damage was bodily set up 1%” above the the “T2” type, did not suffer from slam- base line. No repairs were made then, ming damage, doubtless due to the fact but a yea~ later, after two years Oper- that tankers can be ballasted down. ation subsequent to the installation of the high strength steel, again no dam- An indication of the frequency, the age was found to the high strength location, and the cost of repairs of steel plating, but the damage to the slamming damage for the vessel types af- mild steel plating had been aggravated, flicted is covered in (9).

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