Hull Types and How They Operate
There are two basic types of boat hulls—displacement and planing.
Boats with displacement hulls move through the water by pushing the water aside and are designed to cut through the water with very little propulsion.
- If you lower a boat into the water, some of the water moves out of the way to adjust for the boat. If you could weigh that displaced water, you would find it equals the weight of the boat. That weight is the boat's displacement.
- Boats with displacement hulls are limited to slower speeds.
- A round-bottomed hull shape acts as a displacement hull. Most large cruisers and most sailboats have displacement hulls, allowing them to travel more smoothly through the water.
Boats with planing hulls are designed to rise up and glide on top of the water when enough power is supplied. These boats may operate like displacement hulls when at rest or at slow speeds but climb towards the surface of the water as they move faster.
- Boats with planing hulls can skim along at high speed, riding almost on top of the water rather than pushing it aside.
- Flat-bottomed and vee-bottomed hull shapes act as planing hulls. Most small power-driven vessels, including personal watercraft (PWCs), and some small sailboats have planing hulls, allowing them to travel more rapidly across the water.
How Planing Hulls Operate
A planing hull, when operated at very slow speeds, will cut through the water like a displacement hull.
As speed increases, a planing hull will have a raised bow, reducing the operator's vision and throwing a very large wake. Avoid maintaining a speed that puts your boat in plowing mode.
Your boat is in planing mode when enough power is applied so that the hull glides on top of the water. Different boats reach planing mode at different speeds.
Hull Type Advantages and Disadvantages
|Hull Shapes||Hull Illustrations||Advantages||Disadvantages|
|Flat Bottom Hull||This planing hull has a shallow draft, which is good for fishing in small lakes and rivers.||Rides roughly in choppy waters.|
|Deep Vee Hull||This planing hull gives a smoother ride than a flat bottom hull in rough water.||Takes more power to move at the same speed as flat bottom hulls. May roll or bank in sharp turns.|
|Round Bottom Hull||This typical displacement hull moves easily through the water even at slow speeds.||Has a tendency to roll unless it has a deep keel or stabilizers.|
|Multi-Hull||Another example of a displacement hull, the multi-hull has greater stability because of its wide beam.||Needs a large area when turning.|