Types of Boat Hulls
Posted: February 16, 2022
Types of Boat Hulls: The Complete Guide
If you’re considering buying a boat, there is a lot to know and even more to learn, especially if you’re new to the boating scene. We want to simplify this information and take the overwhelm out of what you need to know about boats.
In the Types of Boats blog, we featured 24 recreational powerboats and detailed what you should know about them. We also included the types of hulls each boat has for your reference.
You may be asking, “What is a hull?” That’s a great question, and we are answering this question and more in this blog.
The hull is the bottom of a boat is why it can float. When the boat is built, the hull is sealed to prevent water from getting into your vessel, which is how it stays afloat.
The hull type determines how your boat will ride in the water at various speeds. Will it glide effortlessly through the water, or will you experience a rough and choppy ride?
We will break it all down for you in this blog.
3 Categories of Hulls
While there are many types of hulls, and it is a feat of great design and engineering when it comes down to what hulls do, they do one of two things: either displace water or ride on top of the water.
What do these terms mean?
We break this down into hull categories:
A displacement hull helps boats move through the water by pushing the water aside and is designed to cut through the water with minimal propulsion. The weight is the boat’s displacement, and boats with these types of hulls cannot go fast. An example of a displacement hull would be a cruise ship. Displacement hulls are very stable on the water and don’t require as much propulsion relative to the weight of their load to other hulls.
These hulls ride on top of the water, also known as planing hulls. These hulls are designed to rise up and glide on top of the water when power is used, which is why powerboats have planing hulls.
Yes, we originally indicated that there are two types of hulls, but there are three. The semi-displacement hulls are a hybrid of both displacement and planing hulls. These hulls displace water at low speeds, but they can lift when at a cruising speed. Typically, these hulls are faster than displacement hulls and more stable than a planing hull. Examples of boats with this hull include motor cruisers and trawlers.
Other Factors Affecting Boat Stability
The hull needs the help of other parts of the boat. Think of it as an orchestra - you need the strings, woodwinds, and percussion for an orchestra to be complete. The same is true for a boat.
Let’s look at the five key parts of a boat. For an exhaustive list, check out our complete guide to boat parts.
Deadrise is an important measurement related to the boat's stability. It is the angle measurement between the bottom of the vessel and the horizontal plane on either side of the center keel. It lets boaters know how well the boat rides.
You will find the keel that runs in the middle of the boat from bow to stern. It is a structural beam whose purpose is to keep the ship stable and in control while moving forward.
For example, the deadrise is zero on a flat-bottomed boat, and on a deep v-hull, the deadrise can be as high as 20 degrees or higher.
The keel is the long, flat blade that goes down into the water from the bottom of the boat. The keel provides counterbalance to the boat, which controls it from being blown sideways in high winds.
The beam is an important part of a boat because it, too, determines the boat's degree of stability on the water. The beam is the width of a ship at its widest part of the waterline. Its formal name is "beam overall" or BOA. To correctly measure the beam of a boat, measure the widest part from the port (left side) to the starboard (right side).
A boat with a narrow beam can go faster than a boat with a wider beam. Yet, a narrow beam does not handle heavy waves.
A wider beam handles rough and choppy water but cannot go as fast since it must displace more water as it moves forward.
Draft is simply the distance between the boat’s keel and the waterline. It is determined by how deep the boat sits in the water. Boats either have a shallow or deep draft.
A boat with a shallow draft can easily navigate in calm and shallow waters, such as a fishing boat, as it easily glides and will not take on any damage from snagging rocks or debris. Shallow draft boats cannot handle rough conditions and are very unstable.
Boats with a deep draft perform well in choppy and wavy waters and are considered seaworthy. Deep draft boats do not do well in inland waters.
Freeboard is the distance from the waterline to the lowest point on your boat’s deck, also known as the gunwales. The freeboard’s measurement is significant to know when operating your boat on certain waters for safety reasons.
If you are boating on bigger lakes or in saltwater, both bodies of water have sizeable waves; and if your boat's freeboard is low, this could be dangerous. The waves could wash over the deck, and your ship could take on water and sink.
An Overview of Hull Shapes
There are many shapes of hulls. Today, more than ever, boatbuilders are expertly engineering and crafting various hulls to offer their customers top-performing boats. They are creatively combining different types of boat hulls in their designs to elevate the boater’s experience.
To make this simple, we are breaking the shapes of hulls down into four designs. These shapes are aligned with a specific hull category.
Let’s dive right in!
Flat-bottomed hulls fall into the planing category. Flat-bottomed boats are ideal for use in shallow water and are extremely popular among anglers who fish in inland freshwater. This hull shape offers a stable ride on calm water, and because they quickly get on plane, they perform well at higher speeds. Flat-bottom hulls do not do well in choppy or rough waters, and you would not use them in the ocean.
Let’s look at the flat-bottomed hull pros:
- Shallow draft can navigate shallow rivers, lakes, and ponds
- This hull sits on the water, giving it excellent stability
- Easily slide over any obstacles in the water
Let’s look at the flat-bottomed hull cons:
- Don’t perform well in rough waters
- Designed for freshwater only
- Not a versatile hull
Round-bottomed hulls fall into the displacement hull category. They offer a soft ride but are not as stable as a flat-bottomed boat and tend to rock back and forth. Examples of round-bottom hull shapes are canoes and sailboats.
Let’s look at the round-bottomed hull pros:
- The rounded shape allows easy travel through the water at slower speeds
- Restricts the quantity of drag on the boat
Let’s look at the round-bottomed hull cons:
- Can be very unstable and can roll and even without a deep keel
Multi-hulls are in the displacement and planing hull categories, and you will find them on pontoon boats, sailboats, and power catamarans. As the name suggests, this shape has more than one hull and offers more stability.
Let’s look at the multi-hull pros:
- Stability because of its wide beam
- Multi-hulls can be up to 30% faster than monohulls
- Creates more space on the boat
Let’s look at the multi-hull cons:
- Large turning radius requiring a bigger area
- Not all are designed for saltwater, such as pontoon boats
- Propellers on planing multi-hulls offer holding ability and higher pitch
V-shaped hulls, a common speed boat hull design, are in the planing category and are the most popular hull shape, especially in the recreational boat arena. Examples of V hulls are powerboats and fiberglass motorboats.
Let’s look at the V-shaped hull pros:
- Smooth ride at higher speeds
- Performs well in choppy or rough waters
- Ideal for inland and offshore
Let’s look at the V-shaped hull cons:
- Can roll or bank when making sharp turns
- More power to go at higher speeds (not fuel-efficient)
- Require larger engine(s)
You now know the basics about hulls and what to consider when you’re buying a boat. Understanding these concepts will help you make the best decision for the type of boat you need.
1. What is a boat hull?
A boat hull is its outer body and gives the boat its shape and is designed to keep water out. Hulls are made of fiberglass, wood, or metal.
2. What type of planning handles rough water the best?
For those boaters who are adventure seekers and love to go fast, especially in choppy water, V-shaped planing hulls perform the best in these conditions. The deeper the V-shape, the better the boat, typically powerboats, can handle rough water since it is a wedge shape from stem to stern and cuts through the water.
3. What is the fastest boat hull design?
This could be an entire blog! We will offer you the simple answer. Going fast in a boat depends on the conditions. The v-hull design performs well as far as speed is concerned in choppy waters such as the ocean. If you prefer calmer waters such as an inland lake or river, flat-bottom hulls can operate at higher speeds.
4. What type of boat has a planing hull?
Planing hulls are designed to rise up and skim on top of the water at high speeds. Boats that have a planing hull include:
- Personal watercraft (PWC)
- Some smaller sailboats