Before you purchase your first boat, it’s helpful to familiarize yourself with basic boat terminology. Start by looking at the most fundamental part of a boat’s design – the hull. This is the portion of the boat’s body or watertight frame that rides over the surface, not including the deck, propulsion system, fitting and rigging. Here we’ll dive into the major hull types and designs.
Boat Hull Types
Hulls are constructed from materials like fiberglass, aluminum, wood and steel. They vary significantly in shape, size and design, which often determine their best application. The core categories of hull types are flat bottoms, deep-Vs, modified-Vs, and multihulls.
Flat Bottom Hulls
A flat bottom hull has almost no deadrise, or angle between the horizontal plane at the keel and the surface of the hull. Flat bottom hulls are stable in calm water and usually have a very shallow draft, which is the depth or distance between the waterline and the bottom of the hull. Flat bottom hulls have no V-shape beneath the waterline.
Deep-V Hulls
V-hulls are wedge-shaped hulls that part the water and reduce pounding when they run at speed. The sharpness of the V is measured in degrees of deadrise. Typically, a V-hull is considered a deep-V when it has 21 or more degrees of deadrise at the transom. Most modern high-speed powerboats like the Intrepid 407 Panacea pictured below ride on a deep-V hull.
Modified-V Hulls
A modified-V hull, also known as a semi-V hull, has a combination of deep forward and flatter aft sections. These hulls have attributes of both the deep-V hull and the flat bottom hull. They have somewhat of a V-shape, though it is not sharp enough to qualify as a deep-V. Boats with a transom deadrise of 21 degrees or less are usually considered modified-Vs. For example, the Robalo Cayman pictured below would fall into the modified-V category with 16-degrees of transom deadrise.
Multihulls
Multihulls are boats with two to three hulls connected by a deck. They come in a wide range of types, shapes, and sizes. A popular example of a multihull boat is the catamaran. Check out our Catamarans Guide: The ABCs of Multihull Boats, to get the full scoop on power and sail catamarans and multihulls.
Boat Hull Designs
A boat’s performance under power or sail depends on the hull’s design. All boat hull types will fit into one of three design categories: displacement hulls, semi-displacement hulls, or planing hulls.
Displacement Hulls
Displacement hulls are hull bottoms that remain in the water at all speeds. These are usually found on slower boats like sailboats and trawlers.
Semi-displacement Hulls
A semi-displacement hull mostly stays in the water, though it benefits from a moderate amount of lift at higher speeds.
Planing Hulls
A planning hull rises up and glides on top of the water at high speed. Planing hulls are designed to move fast when enough power is supplied.
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Editor’s Note: This article was originally published in March 2019 and was last updated in May of 2022.
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