CELLULAR DOUBLE BOTTOM

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G is a bracket plate inside the tank. It .supports the margin plate
and provides a rivet connection to the floor, the bracket being connected
to the margin plate with the vertical angle bar g.

It will be observed from the figure that this bottom section, consisting
of floors, longitudinals, angles, margin plate, the inside bracket and tank
top, forms an independent unit which if buoyant enough could float
as a watertight tank. Indeed this part of the ship is built iirst and
the frame legs put on afterwards.

Fig 20 —Tank Side Arrangement.
The frame and reversed frames are represented by f^ and fy the
frame bar is cut at d, and the reversed frame is bent and riveted
along the top edge of "tank side" bracket H. The bracket is connected
to the margin plate by means of the vertical angle Jt* all as more clearly
illustrated in Figure 20.
Cellular Double Bottom.—Figure 21 illustrates the transverse floor
of a cellular double bottom, abbreviated to C.D.B. This system
of construction has superseded the Mclntyre tanks where water ballast
is carried for practically the whole length of the ship. The C.D.B.
is an integral part of the structure, and being well below the neutral
axis of the ship adds considerably to the strength and rigidity of the
vessel. It also increases her safety by providing a more substantial inner
bottom to resist water pressure in the event of the outer bottom being
punctured by stranding than in the case of the tank top plating of the
Mclntyre system. The Board of Trade measures the depth for tonnage
to the inner bottom plating only, thus reducing the measured volume