As melted lead is to be poured into this space to give the boat the right weight to make it sink properly a bulkhead—that is, a partition—must be cut out of tin and soldered to the hull, on the inside of course, up against the rear end of the ballast tank. The face of the wooden nose against which the ballast tank rests will keep the lead from running out at the front end. As the lead is poured in after the motor is set in place this operation will be described later.
About the Power Plant.—While in a real submarine the power plant—the machine that converts the fuel into power to drive the boat—is a gas engine when it is cruising on the surface, and a storage battery and an electric motor when it is running submerged, in your model it is electricity first, last, and all the time.
That is to say, a battery of dry cells supplies the current to run an electric motor and this in turn drives the propeller; besides, it also furnishes the power needed to work the pusher which controls the air supply through the bicycle valve which I have just explained to you.
The first thing to do toward getting the power plant is to beg, buy, or borrow a small electric motor which will develop not less than 1/30 horsepower and at the same time run on a battery of not more than 3 dry cells.[10]
While the motor can be run to its full capacity on two dry cells it will develop more power on a three-cell battery. Now, to get three dry cells which will fit into the small space that is left in the hull of your model you will have to use rectangular cells.[11]
You will also need a small switch to open and close the battery circuit, and this is fixed to the top of the boat, or deck as it is more properly called; the way it is put on will be explained under the caption of The Superstructure.
When you want to buy one of these switches ask for a porcelain base, single pole, single throw switch. It will cost about a quarter. The way the dry cell battery, the motor, and the switch are connected up is shown in [Fig. 16].
