NOTES ON RIVETS AND SPACING OF RIVETS FOR OIL-TIGHT WORK. 75 
I note he suggests that it might be beneficial to carry a cargo of gasoline on the 
first one or two voyages, so that what he terms the ‘‘rusting-up process” would take 
place and penetrate into the seams. In practice, I am afraid that this would be well- 
nigh impossible, particularly at the present time, when vessels are being used almost 
exclusively to carry crude oil. 
In his paper he touches on excessive length of tanks, and he pointed out that infor- 
mation derived by Lloyd’s Register of Shipping conclusively showed that recurring 
damage was more frequent when the tanks were over 30 feet long. The length of tanks, 
I consider, could go beyond that, provided precautions were taken in the upper portion 
of the tanks by extra stiffening on the bulkheads and the fitting of an intermediate 
swash plate. Extra precautions would also require to be taken in the riveting, or 
additional riveting might be required. Undoubtedly the reason why double riveting 
has been maintained by classification societies, particularly Lloyd’s, is due to excessive 
swash in a seaway, and I think this is reasonable. 
I do not think Lloyd’s have refused conversions except in isolated cases, which 
was probably due to their desire to maintain a high standard at a time when little 
experience had been gained in the case of ships carrying petroleum in bulk. However, 
it was found that there was business for a large amount of tonnage in carrying heavy 
oil only, and they gave a class, ‘‘Carrying oil fuel in bulk, F. P. above 150° F.”” This 
class covered the conversion type and has shown that longer tanks and single-riveted 
center-line bulkheads, single-riveted decks and also single-riveted tank tops have proved 
reasonably efficient for a vessel of this class with oil which is generally crude and highly 
viscous. Also, such a proposition is already approved by Lloyd’s in giving certain 
tankers the class ‘‘Carrying homogeneous cargo of petroleum in bulk,” in which case 
the intermediate and center-line bulkheads are single riveted, the end and cofferdam 
bulkheads being double riveted. 
The limitation to the length of tanks was more the result of Suez Canal regulations 
than anything else, on account of the danger of fire taking place during passage through 
the canal. 
Mr. Frear mentions that double riveting in oil-tight work is now the accepted rule, 
and, as I have said before, I think wisely so, particularly as the tendency is to have 
longer tanks. 
With regard to the rivet spacing, I agree with Mr. Frear that workmanship has a 
great deal to do with the present standards, and if the classification societies (now that 
air tools are in such universal use) would demand subpunching—that is, holes punched 
a size smaller, countersunk to suit the rivet required, and afterwards reamed out to the 
actual size, thus ensuring perfect holes, which incidentally would take away any burr 
on the faying surface of the plate—this, together with efficient bolting up at about every 
third hole, I think they could safely reconsider the question of spacing, particularly any 
portion where strength connections are not the feature. Single riveting, too, might 
even be agreed toin parts. Iam sure the extra cost of subpunching would be more than 
offset in the labor saved in tank testing. 
It may be, now that electric welding is becoming more reliable, and providing that 
one can ensure oil tightness, that single riveting might be more generally adopted with 
welding along one edge. 
With regard to Mr. Frear’s remark as to whether classification societies would permit 
dry cargo on top of double bottoms carrying gasoline, even if the seams were double 
