—— a SS ee 
THE RAISING OF THE DRY-DOCK DEWEY. 151 
the Dewey are very well arranged so that they give a very strong structure and one 
which is also easily handled and controlled in docking vessels. To reduce the num- 
ber of bulkheads would reduce the facility of handling and controlling the dock and 
would also lessen the factor of safetyin case of damage to the bottom. In further ref- 
erence to the supposed leakage through these bulkheads, I might add that, in install- 
ing the manhole covers preparatory to the attempt to raise by compressed air, 
several of the bottom tanks were found to already contain some air, which would 
not have been the case had there been appreciable leakage through the bulkheads. 
In regard to the point brought out by Mr. Donnelly relative to the advisability 
of distributing the pumping units rather than having the control from a central 
point through a single drainage system piercing the various bulkheads, I believe it 
more satisfactory to retain the control from a central point as fitted on the Dewey. 
This method makes it far easier to handle and control the dock in docking vessels, 
and I believe that the small advantage to be gained by distributing the pumping 
units and making the bulkheads tight, which advantage would be manifest only 
under some few possible conditions of submergence of the whole dock, should be 
sacrificed for the much greater gain in ease of control under working conditions. 
The drainage piping of the Dewey was all black ifon pipe. It would have been 
better had this been galvanized, as it would have lasted longer and would not have 
corroded so readily. 
Mr. Donnelly also brings up the point of the advisability of providing reserve 
compartments of sufficient buoyancy to float the dock irrespective of the ballast 
or buoyancy compartments used for operating the dock and he suggests that such 
reserve compartments be provided with their own separate pumping systems. In. 
this connection I understand that, in preparing the design for the Dewey, the ques- 
tion of installing a safety deck low down in each side wall was carefully considered 
and finally abandoned on the ground that, in case the dock were lowered to take in a 
vessel, and, should the structure be then damaged above one of these decks, the 
safety deck would become a positive menace owing to the difficulty of getting the 
water above it to the pumps below. Personally, I agree with Mr. Donnelly that 
reserve buoyancy compartments should be provided and that they are very desirable 
if not positively necessary to insure the safety of the dock. Many things might 
happen below water which would result in accidental sinking. A valve might be- 
come jammed open, pipes might corrode in unexpected or unknown places, one of 
the flexible drain pipe connections between pontoons might give way, the dock 
might be struck by a torpedo or by shells from the enemy, it might be accidentally 
rammed by a vessel in docking, etc., etc.; and damage to one of the large compart- 
ments, Nos. 1 or 7, would be an especially serious matter, particularly if the dock 
were lowered to take in a vessel. 
I think the best, and possibly the only really practicable form of reserve buoy- 
ancy compartments would be obtained by providing a safety deck low down in each 
side wall. The machinery decks should also be made completely watertight. Then 
the spaces above both the safety and the machinery decks should be minutely sub- 
