In order to choose a hull, you need to know what types of hulls are out there and what their characteristics are. There are three basic types of hulls for boats:
- Displacement hull
- Planing hull
- Semi-displacement hull
A boat with a displacement hull is displacing the same amount of water both when moving and when docked. Some of the advantages of the displacement hull is that it moves through the water with relative ease, meaning you need a relatively small amount of horsepower to drive a displacement hull boat forward. However, the speed of the boat is limited by the wave that is created by the hull.
Planing hull boats are somewhat similar to the displacement hull in that when stationary, they also displace the amount of water equal to the weight of the boat. However, when moving, these boats have enough speed and power to overcome its own wave. Basically, planing hull boats are not limited by their hull speed. One of the advantages of a planing hull is that a boat with relatively small waterline length can go pretty fast. This is why small cruise boats and waterski boats, and even water jets have the planning hulls. The disadvantage is that you need a lot more horsepower to get on that plain and rise above the wave created by the boat.
The semi-displacement hull is sort of a compromise between the displacement and planing hulls, it operates in transition between displacement and planning. The displacement is minimized by some hydrodynamic lift. Some of the advantages of this type of hull are that it can cruise faster its theoretical hull speed, has better sea-keeping ability, meaning that it can handle big waves better and carry more weight than a planing hull. The disadvantage is that it requires greater horsepower than a displacement hull and therefore has a shorter range than a displacement hull vessel. This is a good design for boats that have to move relatively quick but also have to be able to handle waves in open seas, for example, power cruisers.
Boat hulls also come in different shapes:
- Round bottom
- Vee bottom
- Flat bottom
Round bottom is always a displacement hull. Usually, sailboats have this type of hull. These boats have great sea keeping abilities. V-shape hulls are most of the time used on power boats. Flat bottom hulls offer good initial stability and are typical for planing boats.
But boats can also have more than one hull. These are ca lled multihull boats, as opposed to the monohull boats. A good example is a catamaran, a trimaran or a proa. The advantage of this type of boats is that they are a lot more stability and do not have to be ballasted down at the keel. This is why they are usually faster and lighter.