If you’ve ever been on a sailboat or any kind of boat, one of the first parts of the boat you saw was its hull and you might not have even known it. Simply put, the hull is the bottom part of a boat that rides in and on top of the water. When a sailboat is under water, it’s accompanied by the keel and the rudder.
Knowing the hull type on your sailboat means you’ll have a better understanding of how your boat operates while it’s out on the water. All in all, the hull of any boat is meant to keep the boat afloat and to ensure minimum resistance against the water while being propelled forward. Now let’s dive into the different sailboat hull types and even some other types of hulls in boats in general!
Main Hull Types
There are two main hull types that we’ll be looking at that encompass the many other types of hulls that vary from these two main types. Depending on the type of boat you have, you’ll be floating around with one or the other. We’ll take a look at what you can expect if your boat has either of these hull types.
The most common sailboat hull type you’ll find out there is the displacement hull, which is very effective at pushing the water aside and powering through it during forward propulsion. A displacement hull is often found not only on sailboats, but also fishing, freight, cruise, and other larger boats.
All boats that have a displacement hull will be limited in their speed based on the waterline length of the hull. Regardless of how much power you use, whether it’s from the wind or motor, the maximum speed can’t be increased. This is why you’ll see people mention the waterline length of a boat’s hull when putting them on the market to sell.
The big advantage of having a displacement hull is that they require far less power to get moving across the water compared to the other main hull type; the planing hull. What this means is that your boat will be able to cruise for a long time with the same amount of energy, which also allows you to carry more items on board.
It’s almost guaranteed that your sailboat won’t have a planing hull since they’re most commonly found on powerboats and personal watercrafts (PWCs), like jet skis. Planing hulls allow the boat to lift itself out of the water, reducing drag and increasing the speed of the boat.
Almost any boat that’s equipped with a planing hull will be able to attain a speed much greater than a boat with a displacement boat. The main reason for this is the lift that’s produced when traveling at high speeds which reduces drag on the water. The maximum speed of a boat with a planing hull is dependent on the horsepower of the engine and how much of the hull can be removed from the water while still cruising.
The biggest advantage of having a planing hull is that your boat will be able to pick up speed quickly and reach a greater maximum speed. This allows for shorter journey times. However, there needs to be a source of all that energy, which comes directly from a combustion engine. The faster a boat with a planing hull goes, the larger the cost of fuel will be.
How Planing Works
The way planing works is actually pretty interesting, so I thought I’d dive into it a bit. Even though a sailboat is virtually guaranteed not to have one, it’s always nice to know how other boats operate while out on the water.
Before a boat with a planing hull actually planes, it starts out acting like a displacement hull. As a matter of fact, a boat with a planing hull needs to reach a certain speed before it starts to produce lift. Before that happens, it’s essentially a displacement hull.
While a boat with a planing hull is picking up speed and lifting itself out of the water, it’s in a plowing mode. You’ll know when a boat is in plowing mode when the bow of the boat is elevated and the boat is throwing a relatively large wake. The goal, however, is to move from plowing mode to planing mode, which requires further acceleration.
Once the boat with a planing hull reaches a certain speed, it’ll leave plowing mode and enter planing mode. As I already described, planing is when the hull is gliding across the water with a smaller amount of the hull dragging in the water when compared to the previous modes. Different boats will start planing when reaching different speeds.
Common Sailboat Hull Styles
Now that we’ve gone over the two main types of hulls you’ll find in sailboats and other types of boats, we have a good foundation for the hull styles you’ll commonly see when out on the water. There are three main hull styles that you’ll see quite often, so let’s take a look at those.
By far the most common hull style you’ll see on sailboats is the monohull, which is simply a single hull. Traditionally, a sailboat will have a monohull and they can be found all over the place. It’s probably the style of hull that comes to most peoples’ mind when imagining a sailboat.
Monohulls on sailboats are virtually all displacement hulls. As we went over previously, this allows your sailboat to cruise for long stretches and has a greater efficiency compared to planing hulls. However, most boats that exist on planet earth are monohulls, including powerboats, which can also be of the planing hull type.
When it comes to a monohull on a sailboat, the only way it can keep its stability is to have a proper keel attached to it. A keel is a wing-like object that sticks out of the bottom of the hull in the water and provides a sailboat with ballast for stability. It’s important to understand how a keel works when operating a sailboat with a monohull since it’s one of the main reasons a sailboat can move forward without tipping.
There are certainly a lot of monohull sailboats out there, but there’s no doubt that you’ll also see your fair share of catamarans. Catamarans are sailboats with two hulls and operate quite differently than their monohull cousin. Catamarans are known to be fast and are likely to outrun most monohull sailboats.
Unlike monohull sailboats, catamarans can be fitted with displacement hulls as well as planing hulls. However, even if they have a planing hull they can still produce a relatively good amount of cruising time and do so rather efficiently.
Catamarans are a bit different than monohulls in the sense that they can reach greater speeds. There are several reasons for this. For one, a catamaran doesn’t need a ballast for stability since the broad stance between the two hulls provides enough stability. This means there’s no need for a large, heavy keel. Second, they’re often built out of lightweight materials that allow the boat to reach a higher maximum speed compared to heavier sailboats. Also, if a catamaran has a planing hull, it’ll have the ability to produce lift resulting in reduced drag on the water and even greater speeds.
Unfortunately, catamarans do have the disadvantage of being more likely to capsize in unwanted high-wind situations. Also, it’s very difficult for a catamaran to recover from capsizing as opposed to a monohull sailboat that has a good ballast from its keel.
You might have already guessed from the name, but I’ll state the obvious anyway. A trimaran is exactly like a catamaran but with three hulls instead of two. Often times you’ll see a trimaran look like a monohull sailboat with a pair of hulls attached to its side.
Similar to a catamaran, trimarans can hit speeds much greater than your average monohull sailboat. As a matter of fact, they’re known to be “unsinkable” under the situation that the hulls on the port and starboard side of the central hull are completely filled up with water.
One of the coolest aspects of having a trimaran is that when it has a planing hull and/or a hydrofoil, the trimaran’s central hull will lift completely out of the water. This gives it the effect that it’s floating across the air, which is the result of lift produced from the planing hull or a hydrofoil. It’s very cool to see this!
Boat Hull Bottoms
Apart from the main boat hull styles, like the monohull, catamaran, and trimaran, there are hull bottoms that pop up in the world of boating that can differ in style and function. These hull bottoms are more of a deeper look at the hulls of a monohull, catamaran, or trimaran, so you can think of them more as a feature of any of the previously mentioned styles of hull.
A very common hull bottom for boats that are derived from the planing hull type is a flat bottom hull. The flat bottom hull is considered to be one of the less stable styles of hulls, especially when confronted with rough waters. However, you’ll often find them on boats that don’t necessarily ride in these situations, including fishing or taxi areas.
- Good for small lakes and rivers due to having a shallow draft.
- Able to hit relatively high speeds once entering planing mode.
- Not good at handling choppy waters resulting in a rough ride.
When it comes to sailboats, you’re most likely going to run into monohull sailboats that have a displacement style hull with a round bottom. While these are the most common hull bottom for sailboats, they can also be found on smaller boats that are used for fishing, canoeing, and other similar kinds of boats.
- Easily moves through the water due to being a displacement hull type.
- When accompanied by a keel, it produces a great amount of stability from the ballast.
- Without a keel, it can roll when entering and exiting the boat as well as when waves are present.
- Less maneuverable compared to other hull styles.
Deep ‘V’ Bottom
If you’re operating a powerboat, then in all likeliness your boat has a planing hull with a deep ‘V’ bottom. Since deep ‘V’ bottoms are found on planing hulls, these types of boats will be able to pick up speed quickly and at high maximums. This is the most common setup for powerboats out on the water.
This is the most common type of powerboat hull. This hull type allows boats to move through rough water at higher speeds and they provide a smoother ride than other hull types.
- Provides a smooth ride compared to its flat bottom rival.
- Good at handling rough water.
- Requires more power to plane compared to its flat bottom rival.
- Cannot handle sharp turns very well resulting in potential rolling or banking.
We took a good look at multi-hull styles like the catamaran and the trimaran earlier, which are the exact style of hulls that have a multi-chine bottom. A multi-chine bottom is a great example of a displacement hull on either a catamaran or trimaran as it’s the most common bottom you’ll find.
- Easily moves through the water due to being a displacement hull type.
- In a multi-hull boat, it has a great amount of stability due to its wide beam.
- In a multi-hull boat, it needs a large area when either tacking or jibing.
Main Parts of a Hull
There’s some terminology I threw around while describing the many types of hulls a sailboat and other types of boats have. As is the case with a lot of activities, learning the terminology is just something you have to do. Thankfully, the terminology will eventually sink in overtime and eventually you’ll be able to ring off any hull terminology that comes up.
The bow is simply the most forward part of a sailboat and, thus, the very front of the hull.
The stern, conversely to the bow, is the most backward part of a sailboat and, thus, the very end of the hull.
The port side of a hull is the left side. I always remember this with the phrase “I left my port on the table”, with the port being wine. This just so happens to also be the side where boats will have a red light turned on at night, which is the color of port wine.
The starboard side of a hull is on the right side. Opposite the port side, in the evening boats will have a green light turned on and will be located on the starboard side of the boat.
Fore is a sailor’s way of saying “forward”.
Aft is a sailor’s way of saying “back”.
A transom is the aft-most (see what I did there?) section of the boat that connects the port and starboard sections of the boat.
The flare of a hull is where the hull starts to form a large angle the closer the hull gets to the deck.
The waterline is the line around the hull where the water touches when under a normal load.
The waterline length, once referred to as the Load Waterline Length (LWL), is the length of the hull where the waterline is located. This is not the entire length of the boat.
Length Overall (LOA)
The length overall (LOA) is, you guessed it, the overall length of the boat. This is measured from the tip of the bow to the end of the stern.
The freeboard is the space on the hull of a boat above the waterline and below the deck.
The draft is the length from the bottom-most part of a boat (the tip of the keel on a sailboat) and the waterline.