The hull, or bottom of a boat, comes in several different forms. Each form has a unique shape that give it certain handling and performance characteristics. Your boat has the hull form that it has to best match the type of boating it was designed for. In general, hulls fall into one of the two following categories:
Planing Hulls: Planing hulls are designed to plane, or ride on top of the water, regardless of the weight of the boat. The flatter the bottom, the easier it is to get on plane. Also, less power is needed to attain high speeds with a flatter hull. The trade off is in handling. Flat hulls do not handle well in rough water. Many planing boats use a shallow “V” shape to ride better in rough waters. This boat has a V-bottom for better handling in rough water.
Displacement Hulls: Displacement hulls typically have a rounded bottom with a teardrop shape running bow to stern. Displacement hulls displace or move, an amount of water equal to the weight of the boat. Displacement hulls are very efficient. Most long range cruising boats such as trawlers and many sailboats use this type of hull. But because of their design, displacement hulls are restricted in their speed to the square root of their waterline length times 1.34. Therefore, a 64-foot boat can realistically only expect a top-end speed of a little over 10 knots. The Ranger Tug pictured here shows several design elements typically found in displacement hulled vessels such as a rounded hull form and a bulbous bow.
Flat Bottom – typically small open boats such as jon-boats. Flat-bottom boats can easily get on plane at high speeds. Typically intended for use on calm waters such as ponds, small lakes, and slow rivers, they do not handle well in choppy or rough water, especially at planing speeds.
Round Bottom – Round bottom boats almost glide through the water. Because round-bottom boats are very efficient at moving through water, most cruising sail and power boats have rounded hulls. Typically, round-bottom boats move at slow speeds. Most boats with this hull type will have a keel, chines, or stabilizers, as the round form will often roll with the waves, and tends to make everyone seasick during rough weather.
Cathedral hull – Cathedral hulls are two or more hulls attached closely together. This combination of hulls allows for much more stability than what is found in other hull forms. The air pocket that is formed between the hulls may also provide lift, helping the boat get on plane more easily and increasing efficiency.
Deep-V hull – V-hulls are designed to operate at high speeds and to cut through rough water, which provide a smoother ride than flat-bottom or round-bottom boats, but are not as efficient and need larger engines to move at similar speeds. The vast majority of the boats sold today have a variation of the V-hull.
Tunnel/Catamaran hull – When you see a catamaran, you are looking at a tunnel hull. Hulls are essentially two deep-v hulls joined by a platform/cockpit area. Tunnel hulls are gaining in popularity, as they offer many of the benefits of other hull designs, such as stability, speed, and roominess with few of the drawbacks. Can operate in virtually any seas, and tends to ride better than monohull boats.