Why Boats Float

How does a heavy boat float?


A boat, or any other object designed to float, is based on a theory by a very old guy, even older than Capt. Matt. Though he is old and, by the way, dead, he was really a cool guy and his name was Archimedes (Ark-i’-meed-eez). His principle, cleverly named the Archimedes’ Principle, explains how things float.

If you fill your bathtub with water, what happens when you get in? The water rises, right? (And sometimes goes over the side.) That is because you “displaced” some of the water with your body and it had to go somewhere. The key to floating is that the object must displace an amount of water which is equal to its own weight.

For example, suppose you had a block of wood that was 1 foot square. Let’s say that this block of wood weighs about 50 pounds. Now say we lower that wood into the water. The wood will move down into the water until it has displaced 50 pounds of water. That means that fifty pounds of water are pushing back up on the block and making it float.

The principle of floating is pretty easy, however, if you want to remain inside the boat and actually get where you want to go, your boat must have “stability” as well as being able to float. Stability means that it is designed not to tip over easily. That doesn’t mean it won’t ever tip over.


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On a large ship like an ocean liner or tanker, the movement of one person doesn’t affect the stability of the ship because it was designed to safely carry lots of weight. But on a small boat, like a fishing boat, your weight and the weight of your gear (and where you put it) has an effect on the stability of the boat.


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A boat is said to “heel” (no not the one on your foot) when it leans over to one side. This is why you never want to sit or step onto the side of a boat. Your weight could make it “heel” too much and it may tip over. You should also balance the weight of all the stuff you bring with you. In a small boat, you and your gear should always stay low and to the center of the boat. When getting into a small boat, always try to step into the center and keep “one hand for yourself and one for the boat.”


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Of course, because you have on your PFD and are displacing enough water to float, you would be okay, just a little wet and cold. If this should ever happen to you and you can’t right the boat (turn it back over), stay with the boat, blow your whistle or yell for help.

So . . . the next time someone says “Whatever floats your boat” tell them about Archimedes and stability and why it’s a very good idea to always wear your life jacket!