We see boats so often in daily life that we may not always stop to ponder the practical side of how they really work. Keep reading to learn more about the basic scientific principles at work behind keeping a boat on the water.
Displacement
At the heart of a boat’s ability to stay afloat are two key components: displacement and buoyancy.
The concept of displacement reaches back to Archimedes, a mathematician in ancient Greece. In his research, Archimedes discovered that the water level would rise according to his mass when he was in a bathtub. This movement of liquids according to submerged objects is called displacement, and it also refers to the amount of water density moved away when a boat sits in or on the water.
Buoyancy
Buoyancy has to do with density. Density is mass, or weight, divided by volume. Because a block of wood has air in it, it has lower density and therefore weighs less than a block of concrete with the same size or volume.
When an object, like a block of wood or concrete, displaces or pushes out water, the water level rises and wants to fall back down and push the object back up.
The wood weighs less than the amount of water it displaces when fully submerged, so the water is able to return and partially push the wood out, keeping the wood afloat. The concrete weighs more than the amount of water it displaces, so the concrete can hold the water back, letting it sink.
Parts of a boat are also high-density and weigh a lot for their size. However, the boat is mostly hollow or also contains low-density materials. Its overall weight is only enough to push some of the water out of the way compared to the size or volume of the boat itself, and the boat stays afloat.
Buoyancy equals the level of water displaced by the object.
Why Boats Sink
Similar to a cup floating in a sink, if water got in over the boat’s edge, or if the boat began to leak, the amount of volume the boat contains would fill with water and weigh more than it does when filled with air. Boats that weigh more sink further into the water.
However, buoyancy, or buoyant pressure, equals the water level displaced by an object as the water level pushes back. While weight does add to a boat's density, the level of water the boat can displace is entirely dependent on the boat's volume, in practical terms, the available surface of the hull.
A boat can stay afloat with more weight until it becomes fully submerged. At this point, the volume, or available hull surface, can’t displace more water than is already onboard. Not enough consequent buoyant pressure from surrounding water remains to push back and counteract gravity, and the boat drops further.
The scientific aspects of displacement and buoyancy can get a little involved, but it’s worth noting the practical side of how a boat functions to get a better perspective on safe handling and an enjoyable day of water recreation.
We hope you found this information helpful! If you want to learn more about boating, we invite you to consult the team here at Howell’s Marine Sales & Service. Howell’s Marine Sales & Service is your local boat dealer serving Chatham, ON, and our neighbours in London. We offer a wide selection of boats for sale and a service department for all your boat maintenance and repair needs.
