SALVAGE EQUIPMENT USED IN RAISING SUBMARINE F-z. 
By Navat Constructor J. A. Furer, U. S. N., MemsBer. 
[Read at the twenty-fourth general meeting of the Society of Naval Architects and Marine Engineers, held in 
New York, November 16 and 17, 1916.] 
The salvage methods used in raising wrecked vessels may be divided broadly 
into two classes. The most commonly applied method consists of restoring the 
buoyancy of a sufficient number of flooded compartments to float the vessel. This 
can be done in a number of ways. The usual method is for divers to make tempo- 
rary repairs to the damaged underwater body. The compartments affected are 
then pumped out. More recently, successful wrecking jobs have been accomplished 
by sealing the decks over the flooded compartments and expelling the water through 
the damaged bottom by means of compressed air supplied from a tender. In 
cases of ordinary grounding, where perhaps no serious damage has been done to 
the underwater body, the vessel can often be sufficiently lightened by transferring 
or jettisoning enough cargo, or other heavy weights, to permit hauling the ship off 
at high tide. All of these methods fall under the general head of restoring lost 
buoyancy. 
The second method consists of mechanically lifting the sunken vessel off the 
bottom and towing it into shallower water, or into dry dock, suspended from the | 
lifting apparatus. This method, while it is not applicable to very large vessels, may 
be the only method possible under the circumstances. This was the salvage method 
that had to be used in raising the F-4. 
The submarine failed to return from a submerged run made outside of Hono- 
lulu Harbor on March 25, 1915. The vessel was definitely located on the following 
day, in 304 feet of water. After making a number of fruitless attempts to drag 
the submarine into shallower water by means of sweeps, it became apparent that 
direct lifting was the only practicable salvage method. 
DESCRIPTION OF WINDLASS SALVAGE METHOD. 
The problem consisted of lifting 260 tons, the submerged weight of the sub- 
marine. Ordinarily, in the lifting method, surface pontoons are used for salvaging 
sunken craft. The lifting cables or chains are taken to the pontoons and are hove 
as taut as possible at low tide. As the tide rises the buoyancy of the pontoons lifts 
the craft clear of the bottom. The pontoons with their suspended load are then 
towed into shallower water until the wreck is again grounded. At the next low 
tide the chains are again hove taut and the process is repeated. Generally, also, 
the pontoons are equipped with flooding and pumping arrangements so as to in- 
crease the lift that can be Snare at each tide. 
