136 THE RAISING OF THE DRY-DOCK DEWEY. 
located on what is called the machinery deck, which is 16 feet 6 inches below 
the top deck of the side wall. The total displacement of the dock in the light 
condition, without a vessel in it, is about 11,000 tons. The central pontoon 
is divided into 14, and each end pontoon is divided into 5 main water-tight 
compartments. These main compartments are still further sub-divided by 
water-tight bulkheads, so that there are 32 water-tight compartments in the 
main pontoon and 18 in each end pontoon, making 68 in all. The general 
arrangement of these bulkheads in the forward half of the dock is shown on 
Plate 65. These compartments havea depth of 18 feet, 6 inches below the 
floor of the dock. 
Combined flooding and draining pipes with quick-acting gate valves 
lead from each of these 68 compartments to a main drain and flooding 
pipe running along in the bottom of the port side of the dock. The valves 
in each main compartment are all operated by one lever in the valve 
house, which is located on the upper deck of the port-side wall amidship. 
The pumping machinery consists of three 24-inch horizontal centrifugal 
pumps and three Babcock & Wilcox boilers. The pump engines are on the 
machinery deck, the pumps themselves being in the bottom of the dock. 
Each of these pumps has a capacity of discharge of about 35 tons of water 
per minute. The flooding of the ballast compartments is accomplished from 
sea valves into the one system of piping which is used for both pumping 
and flooding. The main line of piping is fitted with a flexible connection 
where it passes from the main or Central pontoon to each end pontoon. 
There are stop valves on either side of these connections and also other stop 
valves located in appropriate places in the main line of piping. All sea 
and stop valves are operated by means of hand wheels on the top of the 
side wall. Each ballast compartment is fitted with a vent pipe leading up 
to the top of the side wall. These vent pipes in some cases necessarily pass 
through several other compartments before reaching the top of the side 
wall and the atmosphere. All the ballast compartments are in the bottom 
part of the dock below the dock floor with the exception of compartments 
Nos. 1 and 7, which extend up into the side walls, their tops being formed 
by the machinery decks on each side. These compartments Nos. 1 and 7 
are by far the largest of all the ballast compartments. 
In May, 1910, the blocks of the dock had been prepared for two 
torpedo boat destroyers, which it was intended to dock early in the morning 
of May 24. On the afternoon of May 23, the dock was lowered to a depth 
of 26 feet over the keel blocks, which left a freeboard of 15 feet on the side 
walls. This lowering of the dock a night in advance was in accordance 
with the usual custom so as to have the dock in readiness and avoid delay. 
