SALVAGE EQUIPMENT USED IN RAISING SUBMARINE F-4. 13 
crete ballast was placed in the bottom of each so as to provide a certain amount of 
pendulum stability, otherwise they would have rolled too freely. A 4-inch flooding 
and discharge valve was fitted at the bottom of the end bulkhead of each compart- 
ment. Operating rods were provided for manipulating these valves from on top 
of the pontoons. A 34-inch valve was fitted for each compartment, close to the 
middle bulkhead, for venting and for attaching the blowing-out hose. These 
valves were located in this position so as to keep them clear of the lines and the 
chains. 
The outside of the pontoons was sheathed with Douglas fir 4 inches thick, ap- 
plied in widths of 3 inches. The use of narrow widths made it unnecessary to 
work the planks to the curvature of the cylinders. The sheathing was not attached 
directly to the plating, but was held in place by %4-inch galvanized wire rope. The 
object of the sheathing was to prevent local damage to the plating in case the cylin- 
ders happened to land on anything sharp. The sheathing also served as chafing 
gear between the pontoons. The value of this feature was fully demonstrated in 
the actual salvage operations. In the case of all of the pontoons the wood on the 
side towards the submarine was so badly abraded that it is safe to say that the 
cylinders would have sprung leaks and possibly would have been punctured if this 
safeguard had not been applied. The object in not attaching the planking directly 
to the shell plating was to eliminate the danger of pulling out or loosening the bolts. 
A leaky bolt would have been as disastrous to the success of the undertaking as a 
puncture in the shell plating. The sheathing was fitted in four lengths, each sec- 
tion being held in place by three wire-rope straps. A plank runway was fitted on 
top of the pontoons so as to afford the divers a level platform to stand on while 
placing the clamps. 
The valves in the end bulkheads were protected by heavy timbers. These tim- 
bers also served as fenders for the ends of the pontoons. The valve operating rods 
and end timbers were not placed vertically. This was necessary in order to clear 
the pads at the upper ends of the bulkheads. Three pads were fitted at each end. 
The side pads were intended for lashing across from one cylinder to its mate on the 
other side of the submarine. Such lashings were necessary only while the cylin- 
ders were resting on the bottom, in order to keep them snugly in position. 
Figs. 4, 5 and 6, Plates 5 and 6, show the pontoons in various stages of con- 
struction. 
One of the essential requirements of the plan of operations was that the lift- 
ing chains and pontoons should be placed accurately in predetermined positions 
with regard tothe submarine. This called for mooring the salvage craft, which was 
used as the working base, to four buoys with control for shifting in any direction 
desired. Four wooden mooring buoys Io feet 6 inches square were built for this 
purpose. These buoys were anchored 45 degrees off the port and starboard bow, 
and 45 degrees off the stern of the submarine. 
The salvage craft consisted of a wrecking barge, which had formerly been a 
dipper dredge. This barge was 98 feet long by 35 feet beam. It was equipped 
