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Rivet pacing in Oil-Tight J oints Tankers Create New Problem to Ship Designers and Build- ers -- Conversions Brought Difficulties in Seam Riveting HE present high state of eff- ciency of the modern tanker leaves little to be said on riv- ets and rivet spacing for oil-tight vork that would be both new and conservative; and it may be safely said radical departures from the prac- tice arrived at as the result of years of experience would invite trouble. Riveting is unquestionably one of the greatest, ii not the greatest, item of expense entering into the cost of construction, and the unprecedented gemand for tankers and_ oil-burning vessels at this time magnifies its im- portance. Experience 'has become much more general in both the build. ing and operating of tankers, and per- haps this was thought to be an oppor- tune time to provoke discussion along other than ttraditional lines. Rules governing rivets and spacing of rivets for oil-tight work, as cov- ered by the classification rules of the navy department, the British admir- alty, etc. does not vary radically al- though, on account of higher stresses used, a greater spacing is adopted in gome parts for naval vessels. It must be borne in mind, however, that naval vessels are not subject to the great variations in load encountered in the merchant marine, and therefore the stresses can be anticipated with great- er accuracy. Rules for rivets and riv-: et spacing are the result of evolution arrived at by rule of thumb, experi- ence, size of rivet found practicable to drive, spacing suitable for caulking, experiments, calculations, survey re- ports on damage cases, etc. and, in the opinion of 'the writer, generally are satisfactory with very few exceptions, which will be referred to later. Oil tightness depends more on good workmanship, perhaps, than on any other one thing, especially so far as riveting is concerned. If every rivet could be guaranteed 100 per cent per- fect, slightly greater spacing would be practicable and might be allowed by classification societies, except where a given efficiency of joint is essential. The same standard of workmanship does not exist throughout the yards of the world or in some cases even throughout the same vessel. It is ob- vious there must be a common rule for all and the required rivet spacing is designed therefore to guarantee From a paper read by Hugo P. Frear, member, at the twenty-eighth yeneral meetinz of the Society of Naval Architects and Marine Engineers, New York, ttle when new. good results for the average standards of workmanship. It was stated above that the rules for rivets and spacing of rivets for oil-tight work had been arrived at by a process of evolution, and it may not be out of place 'to refer briefly and in a very general way tto some of the early bulk oil carriers and to some precedents in connection with conver- ' sion jobs on account of the large number of vessels which thave been and will be converted to carry fuel oil. While there were probably some barges in existence prior to 1872, it was in tthat year the first bulk oil-car- rying steamer was built at Palmer's, Newcastle on Tyne, England. Al- though this vessel was built especially for carrying oil in bulk, she had a double bottom, and the indications are the rivet spacing was the same as in vogue at that time for water-tight work. Following this date, new bulk oil carriers were built from time to time; but for about three decades con- verted vessels contributed more or less to increasing the fleet. . During this period the spacing of rivets, even for water-tight work, was in some respects greater than at. pres- ent and vessels frequently leaked a But they were built of iron and the joints soon rusted up tight, thereby increasing the friction of the riveted joints and resulting in stronger and more durable vessels un- der existing conditions. This rusting- up process, however, would not take place in the case of new vessels built to carry crude or lubricating oils in bulk, and on that account some of the converted vessels were tighter than new tankers. It was during this pe- riod that the importance of the fric- tion of the joint referred to above be- came more generally appreciated. Gasoline Aids Oxidation Oxidation takes place in tanks car- rying gasoline, and this rusting-up process penetrates into the seams. On this account it might be beneficial to carry a cargo of this character on the frst voyage or two as is sometimes done. Tests have demonstrated that, while the friction of the joint has no effect on the ultimate strength, it has a safe factor above working stresses where workmanship is good. If there is the slightest slip, defective rivets will come to light. Therefore, in oil- tight work intimate metal-to-metal : 27 contact is of the greatest importance for permanent oil tightness especially where subject to alternating stresses set up by the working of the ship. Serious recurring damage, constant necessary repairs and resulting cost. to underwriters during much of this part of the history of oii carrying in bulk were attributed to inadequate scant- lings, improper distribution of mate- rial, insufficient riveting, poor work- manship, long tanks, overloading and limited knowledge of manipulating large quantities of water ballast, es- pecially in the case of exceptionally long tanks. Investigation by Dr. James Montgomerie over a period of thirteen years prior to 1909 conclu- sively showed recurring damage was more frequent where the tanks were more than 30 feet long. Early tank- ers, both new and converted, had rela-. tively less beam and were conse- quently easier in a seaway, yet the penetrating character of the oil sought out weak spots and loosened rivets developed under new stresses created by carrying oil in bulk. The first leaks frequently occurred at the ends of stiffeners and in rivets connecting frames to shell, which were subject to stresses not common in ordinary ves- sels. After these started the vessel began to. work more, and progressive damage followed, frequently resulting in almost entirely reriveting the ves- sel. There was a fad about this time for plug-headed rivets, but these were abandoned because they would not draw the work up sufficiently close and created greater difficulty in secur- ing high quality of workmanship. The old reliable pan head was found to' produce the most intimate contact and to be more permanently oil-tight and was recommended except where some other types were absolutely nec- essary. Up to 1894 there were built or building to Lloyd's classification sixty- four tankers, yet the society did not consider that it had sufficient expe- rience to lay down definite rules for their construction. In this year, how- ever, Benjamin Martell, chief surveyor io Lloyd's Register, read a paper be- fore the Institution of Naval Archi- tects wherein he outlined his views on details of construction and _ riveting for bulk oil carriers, recommending three diameters for oil-tight work. This paper was distributed and for a number of years served as a guide to