The easiest way to classify a boat is based on the number of hulls that it has. That would put a boat in either one category or another, the two being the monohull and the multihull. There are obvious sub-categories for each one, but beyond the simple number of hulls used there is also the matter of the shape that the hull takes, and we’ll cover all that below.
The monohull uses a single hull as you would expect and it’s the traditional shape that is used in the vast majority of the sailboats you will see these days. In order for the single hull to remain stable on the sea it uses ballast that usually is around 30% of the boat’s weight. The maneuverability is not as good thanks to this system and the acceleration suffers as well.
In this category you will find a few different types. You’re getting a boat that has two, three or more hulls that are connected to one another with some kind of frame. Depending on the number of hulls it can be a catamaran (2 hulls), a trimaran (3 hulls) and so on.
The advantage of the multihull configuration is the fact that these boats occupy a bigger area, allowing for more stability and not needing ballast anymore. That makes the boat faster and lighter, more difficult to tip over (though very hard to recover if they do). In many cases they have flotation chambers that are filled with foam. It is said that commercial trimarans built these days can’t sink even if all the compartments of the crew are filled with water. At the same time, it takes very little time to get to the maximum possible speed and that speed is actually higher than for a monohull boat. Some disadvantages do exist, among them the fact that they’re more difficult to use against the wind and they lose their speed faster in these situations.
Types of Hulls
While there are multiple ways one could classify hulls, the most used method puts them in these two big categories:
Hard-chined and Chined: these hulls have a minimum of one area that is more pronounced along their length and they include multi-bottom hulls, v-bottoms and flat-bottoms.
The hulls with flat bottoms come with a higher drag, but also offer more initial stability. They work best in boats that are to be used in inshore waters that are sheltered, since they don’t do as well on sailboats.
Multi-chined hulls: These have a form that is curved, offering smaller drag when compared with the flat bottom. They’re difficult to make but they make for better boats.
Soft-chined, round bilged or moulded: these are defined as having smooth curves and examples are the s-bottom hulls, the semi-round bilge and the round bilge.
The one that’s most often used right now is the one called round bilge. It offers higher speeds thanks to smaller resistance when it has a small load, or a smoother ride when the load is large.
The advantage of the s-bottom hulled boats is the added comfort that the boat’s occupants feel, thanks to the reduced amount of rolling that the boat has.