om of the hull, to the top of the other
side. Having cut the tin to the required size, one side is put in place
with small nails, spacing them an equal distance apart.

Before securing the opposite side, the builder must first arrange the
inlet-valve. This particular member is constructed as follows. First,
obtain an old gas-pipe union which measures about 5/8 inch in diameter
and 3/4 inch long. With a hacksaw this is cut off in a sloping direction
with an angle to correspond with the slope in the bottom of the
dry-dock. When this is done, a lid must be fitted to the top by means of
a long rod, as clearly shown in Fig. 122. On the under side of this lid
a small piece of sheet rubber should be glued, so that when the lid is
screwed down the valve will be made water-tight. The valve must now be
soldered to the inside of the hull. It is placed in such a position that
it will rest just under the center of one of the upper decks when the
controlling rod is upright.

[Illustration: FIG. 122]

The top end of the rod must contain a thread for about 1 inch, and a
round plate made to screw on. This plate should be about 3/4 inch in
diameter, and contain three small holes around the edge. These holes are
used in fastening the plate to the deck. The top of the rod is fitted
with a small crank-handle, which is used in turning the rod in either
direction. In this way the valve can be either opened or closed. At the
bottom of the rod a small swivel should be provided, as indicated in
Fig. 122.

The plate or sheet of tin on this side of the hull can now be
permanently fixed in place. When this is done a light hammer should be
used around the edges to turn the tin into the wood.

With the plates secured in place, the builder must next fix a flat wood
keel along the bottom of the dry-dock. This should be screwed to the
inside keel, screws passing through the tin plate. A lead keel is then
screwed to the wooden keel, and when this is done the dry-dock can be
launched. If the foregoing instructions have been carried out carefully
the dry-dock should ride lightly on the water.

As a trial the inlet-valve is now unscrewed and water is permitted to
enter the hull. When the water rushes in, the hull will begin to sink.
The water should be allowed to enter until the hull sinks to within an
inch of the lower or inside deck. The valve should then be closed. The
exact position of the water should now be found, and a line drawn all
around th