12 SALVAGE EQUIPMENT USED IN RAISING SUBMARINE F-4. 
on and under the water with the greatest expedition possible once it was started, 
because of the danger of being overtaken by heavy seas at any moment. It was 
particularly important that once the first pontoon was landed there should be no 
delay, because a heavy swell would probably have wrecked the pontoons against 
the sides of the vessel. 
DESCRIPTION OF PONTOONS. 
Four of the pontoons, the bow and stern pairs, were made 32 feet long by 11 
feet in diameter. The other two were made the same length but were 12 feet 6 
inches in diameter. The buoyancy—that is, the lifting capacity—of the 11-foot 
cylinders was 63 tons, and, of the larger cylinders, 84 tons. The combined lifting 
capacity of the four pontoons was 420 tons. This provided excess capacity of 160 
tons over the estimated weight of the submarine. Not only did this margin insure 
the necessary pull which might be needed to start the vessel, but it also provided 
for any failure to realize all the buoyancy available which would result should any 
of the cylinders become cockbilled to such an extent as to make it impossible to un- 
water them completely. It was correctly assumed that the full lifting capacity of 
the cylinders could probably not be developed, due to this cause. The weights of 
the cylinders were 63,000 pounds and 73,000 pounds respectively. The pontoons 
and their collateral equipment are shown on plans reproduced as Plates 14 and 15. 
Securing the pontoons to the submarine was one of the most important fea- 
tures of the salvage arrangements. The plan adopted was very simple and proved 
entirely successful. Chains were rove under the vessel and, while the pontoons 
were afloat, were brought up through the hawse pipes already mentioned. These 
hawse pipes were 12 inches in diameter fitted 8 feet from each end of the cylinders. 
They were built up of steel castings connected by 12-inch pipes. After the pon- 
toons had been landed on the bottom, cast steel clamps were bolted around the 
chains just above the hawse pipes. The clamps were made in halves molded to the 
shape of the links. The two halves were drawn together and kept from spreading 
by four heavy bolts. The clamps were of such length that they bridged the hawse 
pipes and therefore could not slip through when loaded. Fig. 3, Plate 5, shows a 
clamp attached to one of the chains. The details of this feature are also shown in 
Plate 15. 
Fifteen-pound plating was used for the shell of the pontoons. The frames, con- 
sisting of 5-inch by 3-inch angles, were spaced 2 feet apart with web frames in the 
wake of the hawse pipes. Fore-and-aft girders of 1214-pound plating were fitted 
go degrees apart. These girders and the web frames were riveted to the lugs of 
the hawse-pipe castings, thus providing a very substantial construction for the 
support of the large concentrated loads at these points. 
A transverse watertight bulkhead was fitted at mid-length dividing the pon- 
toons into two compartments so as to facilitate sinking and blowing out. Without 
this bulkhead the cylinders would have been difficult to handle while being lowered 
into place, as there would have been no way of adjusting the trim. Two tons of con- 
