Can a boat flip over?

Sean and Robot have been investigating why boats collapse and what can be done to prevent it.

Ships are designed so that they cannot easily capsize or flip over.

The center of gravity of a boat has a lot to do with whether or not it capsizes. Gravity is commonly thought of as a force that pulls things downward (toward the center of the Earth), but this is not always the case. Gravity can cause objects to turn and topple, especially if they are high off the ground and unbalanced.

Despite this, all objects behave as if their mass (the stuff they’re made of) is concentrated at a point known as their center of gravity.

A simple object, such as a ball, has its center of gravity in a very obvious location – right in the center. However, in a more complex object, such as your body, the center of gravity is slightly higher than your waist because the top half of your body is heavier than the bottom half.

If you’ve ever climbed around on a rowboat tied to a jetty, you’ll understand how unstable small boats can be when loaded. When you stand on a cruise, you efficiently become a part of it, altering its center of gravity and instantly elevating it.

Also, because you enter a boat from the side, the moment you step on board, your center of gravity shifts to where you’re standing. The center of gravity is no longer above the center of the boat, causing the entire thing to rotate towards you.

A boat can swing from side to side fairly freely, and because it is light, it only requires a small force to move in the water. All of these factors combine to make it relatively easy for a small boat to capsize. Sitting down in a small boat lowers the center of gravity, making it more stable. In general, the lower the center of gravity, the more stable the boat.

Large boats frequently have heavy engines beneath the water level, giving them a low centre of gravity and making them more stable. They also have a large keel, which is a vertical board that runs from back to front along the central “spine” of the boat. The keel prevents boats from rolling (moving side to side) or capsizing.