A MODEL FLOATING DRY-DOCK
AS many of the readers probably know, a dry-dock is used in assisting
disabled vessels. Some dry-docks are permanent, while others are built
so that they can be floated or towed to a disabled vessel that is not
able to get to a land dry-dock. The land dry-dock operates as follows.
It is first filled with water, and the disabled boat is towed in by
tugs. After the tugs leave, the gates are closed, and the water in the
dry-dock is pumped out, leaving the boat high and dry. Large props are
put in place to prevent the boat from tipping.
The dry-dock here described is a model that is towed to a disabled
vessel. It is then sunk until it passes under the boat. The sinking is
brought about by filling the dry-dock with water. After it has sunk to
the proper depth it is passed under the boat to be repaired, the water
is pumped out, and the dry-dock rises, lifting the disabled boat with
it. Repairs can then be made very easily.
The model here described does not possess all the fittings and additions
of the original. However, it is able to rise or sink as required,
carrying the machinery necessary to bring about these functions.
[Illustration: FIG. 120]
[Illustration: FIG. 121]
A general view of the completed model is shown in Fig. 120. The first
part to construct is the framework for the hull. Four pieces of wood
will be required for this, and they should be cut to the shape and size
shown in Fig. 121. To make this it is best to cut the two side parts
first, as indicated by the dotted lines. This done, the bottom piece can
be clamped on from behind by means of pieces of lath. These are for the
two end pieces. The other two pieces are made in the same way, except
that they contain holes for the water to pass through, as shown at _B_.
The wood for these frames, or ribs, should be not less than 1/4 inch
thick in order to accommodate the pieces used in the construction of the
remainder of the hull.
When the builder has made the four ribs, he should proceed to construct
the lower deck, which consists of a single piece of wood nicely planed
and finished, measuring 14-1/2 inches long by 8 inches wide and 1/8 inch
thick. This piece must be nailed to the bottom of each of the ribs, one
at each end, and the other two containing the holes at equal distances
apart. Tiny nails, similar to those used on cigar-boxes, will be found
very suitable for this work. Some old cigar-boxes may be broken apart to
obtain the nails for this purpose. Before nailing on the board it should
be marked out to present ordinary deck-boards. The reader is referred
back to Chapter 9 which describes this process, using a straight-edge
and knife.
When this board is nailed in place, the next requirement will be two
pieces for the sides the bottom edges, of which must rest on the top of
the deck-board. These boards are the same length as the deck. They
should reach to the top of the ribs, and be fastened in the same way as
the bottom deck. It is good practice, when doing this, to place a little
white lead on the bottom edge before finally driving the nails in place.
This will tend to produce a water-tight joint. This done, three pieces
of wood 5/8 inch square must be screwed in place, flush with the bottom
ends of the ribs, to form a flat keel. They should be firmly fixed since
a lead keel is afterward screwed on the bottom of the boat. Attention
should now be directed to fitting the two middle decks. These are placed
4 inches from the top and are 4 inches wide. In this space the engine
and pumps are placed. Therefore, the top deck is made in the form of a
lid, and the outside plate made to draw out. In this way the mechanism
below the deck can be made very accessible.
The framework of the dry-dock is now completed, and the builder can
proceed to fix on the side plates. These are made from sheet tin with a
width of 14-1/2 inches. The length must be sufficient to reach from the
top of one side, around the bottom 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 the hull, which can afterward be painted in.
The engine and boilers must now be constructed and placed on the
dry-dock, so that the water that was permitted to enter may be pumped
out. As a temporary arrangement, a thin rubber tubing is inserted
through a hole in the lower deck and allowed to hang outside the
water-level. The siphon can then be formed by simply drawing the water
up by suction with the lips. A continuous flow will result, emptying the
hull within a short time.
[Illustration: FIG. 123]
Attention is now directed to the construction of the boiler and pumps.
The boiler, which is rectangular in shape, is made of thin sheet copper,
and measures 4 inches long by 3 inches wide by 2 inches deep. A hole is
made in the top, and a brass or copper tube 6 inches long and about 3/4
inch in diameter is soldered in position, as depicted in Fig. 123. This
tube acts as a chimney on the dry-dock, but it is really used for
filling the boiler, and the top is supplied with a tightly fitting
cork.
The ends of the boiler also act as supports, and they are made 4 inches
long. The bottom edge is turned up for about 1/4 inch to enable the
boiler to be screwed firmly to the lower deck. The boiler occupies a
position at one end of the hull, and should fit easily in between decks.
A small spirit-lamp is used to furnish heat, and no description need be
given of this particular part of the equipment. Before the boiler is
firmly fixed in place a small hole should be made near the top at one
end. The feed steam-pipe is inserted in this, and soldered in place.
Two small oscillating cylinders, similar to those made for the engine on
the _Nancy Lee_ (Chapter 6), should be made. They should not be more
than 3/4 inch in length, with a 3/8-inch bore. If the builder has any
old model steam-engines in the shop, he may take the cylinders from them
instead of constructing new ones for the dry-dock.
The engine is set up as shown in Fig. 124. The first job is to make the
frame or standards, and this is in one piece. Two pieces of brass (_A_),
measuring 5-1/2 inches long by 1/2 inch wide and 1/16 inch in thickness,
are cut. Next the builder should mark off 1-1/2 inches from either end,
and carefully bend at right angles, after which holes are drilled to
accommodate the crank-axle _B_. Two holes must also be made for screws
to enable the machine to be screwed to the deck.
[Illustration: FIG. 124]
[Illustration: FIG. 125]
The flywheel should be 1-1/2 inches in diameter, while the bent crank
has a throw of 3/16 inch. The steam-cylinder is fixed on the outside of
one of the uprights, and the steam-pipe must, of course, be fitted from
the inside.
The pump-cylinder is composed of a small piece of brass tube 1 inch long
and 3/8 inch in diameter. The plunger is 1/2 inch long, and the diameter
is just sufficient to enable it to work freely up and down inside the
brass tube. One end is shaped as shown in Fig. 125. This contains a saw
cut that enables the pump-rod to be placed between and connected with a
pin. The bottom end of the cylinder is now fitted with a brass disk in
which a hole is made and a 3/32-inch tube soldered in place. The inside
surface of this piece of brass should be countersunk, and the piece is
then soldered into the end of the cylinder. Before the plunger is
inserted a small lead shot is dropped in, which should be larger than
the hole at the bottom of the cylinder, thereby covering it. A hole is
drilled in at the side of the cylinder, and a small bent pipe fixed in
it. At the top of this pipe a short piece of 3/8-inch brass tube is
fixed in place, as indicated. This piece of tubing is closed at both
ends. The bottom end is treated like that of the pump-barrel and
supplied with a large shot. An outlet-pipe is soldered into the side of
the delivery-valve chamber and leads to the side of the hull.
The pump _E_ is fixed at the bottom midway between the engine uprights
as indicated in Fig. 124. The suction-pipe passes through a hole and
down through the deck nearly to the bottom of the hull. After the
engine and boiler are connected, a trial can be made. If the foregoing
instructions have been carried out, the engine will run at a good speed
and a continuous flow of water will be pumped out of the hull. All parts
of the engine and pump should be carefully oiled and water should be
poured into the pump in order to prime it before its start.
It is understood that two complete boilers and pump units are made for
the model, and one is mounted on each side. If the builder desires to
increase the capacity of the pumps and install a more powerful boiler
and engine, only one pump will be necessary. Otherwise the water will
not be pumped from the hull very rapidly.
When the builder has finished the pump units, he should turn his
attention to the remainder of the fittings. Two small cranes are made,
and one is placed at each side of the hull. They are made of tin. The
cab of each crane measures 2-1/2 inches high by 2 inches long by 1-3/4
inches wide. A small roof is fitted on, and a piece of wood fitted to
the bottom to serve as a floor. The jib measures 6 inches long by 3/4
inch at the base, and tapers to 1/2 inch. It has 1/4 inch turned down at
each side, thus adding considerable strength. The jib is fitted to the
cab by means of a wire passed through the sides, and two guy-ropes are
arranged as shown. A small piece is now cut out at the top, and a pulley
wheel fixed in position by means of a pin passed through the sides.
[Illustration: FIG. 126]
The winding-drum can be made of either tin or wood. The axle passes
through both sides of the cab, the crank being attached to the outside.
Fig. 126 shows the completed crane, which is held to the deck by means
of a small bolt and nut. A washer should be placed between the bottom of
the crane and the deck, to allow the crane to turn freely with little
friction.
A hand-rail, made of fine brass wire, is placed around the deck.
Dummy port-holes are fixed to the sides of the dry-dock for the purpose
of lighting up the interior of the engine-room. These are furnished from
top rings taken from gas-mantles. Anchor-chains are fixed at each end of
the dry-dock. The whole dry-dock is painted with two coats of gray paint
and the water-line painted in bright red.
[Illustration: FIG. 127]
Fig. 127 shows the dry-dock with a model boat in position.