SALVAGE EQUIPMENT USED IN RAISING SUBMARINE F-4. 15 
and close to the submarine, the vents were opened for complete flooding. In the 
case of one pontoon one end had to be lifted and swung in closer to the vessel. 
This would have been difficult had the pontoon been completely filled with water 
before the adjustment was attempted. The flooding valves were closed after the 
pontoons had filled completely, in order to prevent the entrance of sand. 
Although the negative buoyancy was kept well in hand by careful venting, the 
cylinders, nevertheless, showed a decided tendency to become unmanageable and 
heavy as soon as the water plane area had vanished. All of the pontoons were, 
however, lowered without mishap and without parting lines. 
The divers began bolting on the clamps as soon as the position of a cylinder 
was reported as satisfactory. It was not essential that the clamps for the first low- 
ered pontoon of a pair should be fitted to any particular link, but, once fitted, it was 
necessary to know exactly the link on which each was placed so that the clamps on 
the opposite side might be placed correctly, this in order to insure that the proposed 
amount of slack was left in each chain. If the chains had been hauled up snugly 
and the clamps had been placed directly above the hawse pipes, the pontoons would 
have been held down alongside the submarine on becoming buoyant. This would 
have brought a considerable crushing stress on the sides and would have been par- 
ticularly objectionable, because of the excessive stress to which the chains would 
have been subjected. 
UNWATERING THE PONTOONS. 
After considering various methods of unwatering the pontoons, the use of com- 
pressed air taken from torpedo air flasks was decided upon as the simplest and 
most reliable method. Calculations indicated that 20 torpedo air flasks blown down 
from 2,150 pounds to 200 pounds pressure would furnish enough air to raise the 
vessel. In order to maintain a rapid flow of air from the flasks it was proposed 
to blow down to only 200 pounds. Tests were made which demonstrated that a 
flask could be blown safely from 2,150 to 200 pounds pressure in about five min- 
utes against a receiver pressure of 50 pounds. A test was also made on the flow 
of air through a 150-foot length of 34-inch hose, using a differential pressure of 
25 pounds per square inch. From this test it was found that the flow was consider- 
ably greater than given either by Halsey’s or Kent’s formule. On the basis that 
the air would be delivered to the pontoons by twelve 150-foot lengths of 34-inch 
hose against a water head of 46 feet and with a differential pressure of 20 pounds, 
it was calculated that the cylinders could be unwatered in about 100 minutes. 
When this stage of the work was actually reached, the differential pressure was 
kept somewhat below 20 pounds as a precaution against starting the seams of the 
end bulkheads of the pontoons. The cylinders were actually unwatered in about two 
hours after air was fully turned on. 
Twenty-four torpedo air flasks were installed on a coal barge, as shown in Fig. 
10, Plate 8. These flasks were connected in parallel to a 7-inch extra-heavy pipe. 
This pipe discharged into an expansion chamber made from a piece of cast-iron pipe 
