LETTERS Iron vs. Steel in Shipbuilding O laf E ngvig's article on iro n vs. steel in shipbuilding was very interestin g to me; I am a retired marine engineer with som e kn owledge of wrought iron and steel. I was, whar is called in the U nited States, a "port engineer," and, as such, I arranged fo r and supervised d rydocki ng of commercial vessels. They were all steel hulls. O n o ne d ryd ocking in New York H arbor som etime in rhe earl y 1970s, rhe vessel next to mine was a US Arm y Corp of Engineers dredge nam ed Ezra Zanzibar. H er port en gineer and I spent coffee breaks together discuss ing our wo rk and the quality of workmanship that we were each receiving from the shipyard. Borh sh ips we re having steel hull plates replaced . His vessel was a rive ted wro ught-iro n hull fro m the !are 1800s; m ine was a World Wa r II-vintage steel hull. Th e decisio n to replace sreel plates in sh ipyard was based o n thickness measurements, whi ch was a ro utine meth od in the 1970s. H e showed me where rhe o ri ginal wrough t- iron plating on his ship was still in excellent condition with minim al thickness loss . Wherever rhere was any dam ageJ hull platin g, however, ir had to be replaced with steel because wro ughr iron was not available anymore. H e pointed o ut rhar riveting a steel plare between wrought iro n set up a galvanic cell and only has tened rhe deteri oratio n of rhe sreel . H e no red rhar these same sreel plates had been replaced befo re. His vessel spent a large po rti o n of its time in fresh water, so the corrosio n was not o nl y due to saltwater service. Yo u probably have heard many sto ries like this, but after readin g M r. Engvig's article, I had to bring one m o re story to yo ur arrention. There is a graveyard of 1800s wooden vessels burned to the wa terline near where I li ve in New Jersey. The no ticeable remains on most of these are their rudd er posts, which I assume were wrought iro n. I graduated from Kings Po int in 1962 and we studied bas ic metallurgy there, but afrer rhe dozens of drydockings and hundreds of o ther repairs, yo u learn on-rhe-job merallurgy. Ano ther example rhar I becam e intimate wirh was bro nze propeller fa ilures. A real old-rimer propeller repair shop owner po inted our rhar rhe T-2 ranker propeller that I senr in fo r rhe repai r of a damaged blade tip had anorher problem . H e called ir "mud acid" (dark spors all over rhe bronze). Afrer losing entire blades off two of rhe T-2
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reducing rhe po tential fo r leaking seam s. I do no t co ncur wirh Mr. Engvig's asserti o n that fo r mo re rhan a cenrury, rhe "authorities" had argued that steel was mo re corrosion resistant than iron . M y dog-eared copy of the 194 1 edition of M arks' M echanical Engineers Handbook, purchased while I was a student of naval architecture ar M IT in 1942, states that wrought iro n "is said to be superi o r to mild steel in resistance to corros ion." The superiori ry of w rough t RAY SCHMIDT Woodbridge, New Jersey iron to black steel fo r fresh water piping was recognized throughout industry; however, I enjoyed O laf Engvig's article on iron vs. when choosing a m aterial for use in a parti custeel in your recent issue, bur I think he lar application, the des igner must consid er complerely misses rhe poinr of why sreel man y mo re of its properties than longevi ty, so rapidly replaced wrought iron as a ship- and by th e 1890s steel's all-around superib uilding material. Me rchant ships are builr o ri ry fo r shipbuilding was well recogni zed . for one reaso n-to earn m oney. To ensure En gvig states flatl y "as soon as newer rh ar rheir hulls wo uld las r fo r a century o r tonnage of steel was available, they [those mo re, long after rh eir machin ery wo uld be anonymous "authorities"?] scrapped their wo rn out, was never a design requirem enr iron vessels." I believe rhar rhe ac tual case of an y ship wirh which I am familiar. Sreel was rhar as soon as rheir iron ships, fo r an y has many economic advan rages over iron. reason, becam e uneconomical to operate, Ir is stronger rhan iro n, so need not be as rhe owners re placed rhem wirh steel o nes. rhi ck to res isr rh e same loads. This res ults Rather than by im plication criticizing so me in a lighter hull. Altho ugh o ri ginally m ore long-d ead designers for nor accomplishing expensive per ton rh an iro n, by 1880 rhe somethin g rh ar rh ey never ser our to do, prices of sreel and iron were abo ur equal, we should be grateful rhar the designers o f so rhe lighter hull was chea per as far as m a- rhe earlies t meral ships, by using the o nly terial cost was con cern ed. (Later rhe price material avail able to rhem ar rh e rime, inper to n of steel dropped well below that of adve rtently produced a few h ulls rh ar, w irh iro n. ) Steel could be ob tained in lo nger and a grear deal of luck, survived to becom e wider plares, which reduced the number of museum arrracri o ns today. riveted joints required to connect them, SAMUEL G. M O RRISON furth er lowering constru ctio n cos ts and also Easr Lyme, C onnecticut rankers rhar I rook care of, I determ ined rhar rhe de-zincificario n (mud acid) was caused by rh e lack of good groundjn g of the propeller shaft after installing a Brand X (cheap) impressed currenr system in place of zinc anodes on rhe srern fram e. One ship losr rhe blade our in to rhe ocean and li mped in wirh grear vibratio n. O n the o rher ship, rhe blade we nr ri ghr rh ro ugh the after peak ran k.
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