What if the hull of a boat has a hole in it? If the hole is below the water-line, water will leak in and in time completely fill the inside of the hull, causing the boat to sink. Also, if too great a load or cargo were placed in a boat, it would sink. It must be understood that water leaking into a boat increases its load, and if it is not stopped it will cause the boat to sink.
The center of gravity of a boat is a very important matter. First, attention will be directed to the meaning of "center of gravity." If a one-foot ruler is made to balance (as shown in [Fig. 3]) at the six-inch mark, the point at which it balances will be very close to the center of gravity. The real center, however, will be in the middle of the wood of which the rule is composed. It should constantly be kept in mind that this "center of gravity" is a purely imaginary point.
Look at [Fig. 4]. If wires are arranged in a wooden frame, as shown, the point where the wires cross will be the center of gravity if the square formed by the wooden strips is solid. Every body, no matter what its shape, has a center of gravity. The center of gravity is really an imaginary point in a body, at the center of its mass. Oftentimes engineers are heard saying that the center of gravity of a certain object is too high or too low. [Fig. 5] shows the center of gravity in a boat. If the center of gravity in a boat is too high (as illustrated in [Fig. 6]) the boat is said to be topheavy and unsafe. When a boat is topheavy or its center of gravity is too high, the boat is liable to capsize. In fact, some very serious marine accidents have been caused by this fault.
The center of gravity (or center of weight) in a boat should be as low as possible. A boat with a low center of gravity will be very stable in the water and difficult to capsize. This is true of model boats just as much as it is true of large boats. The model boat builder must keep the weight of his boat as near the bottom as possible. For instance, if a heavy cabin were built on a frail little hull, the boat would be very unstable and would probably capsize easily.