Hull Speed Calculator

Hull speed is the theoretical maximum speed at which a displacement hull vessel can travel efficiently. At this speed, the vessel's waterline length equals the wavelength of its own bow wave. Trying to exceed hull speed requires disproportionately large amounts of power because the boat is effectively trying to climb over the wave it creates.

The standard hull speed formula is V_hull = 1.34 × √LWL(ft), where LWL is the waterline length in feet and the result is in knots. If you're working in metres, convert first: LWL(ft) = LWL(m) × 3.28084. An equivalent metric constant is approximately 2.43 × √LWL(m).

Hull speed sets a practical upper limit on how fast a displacement vessel can travel without a massive increase in engine power or sail area. Naval architects and sailors use it to understand a boat's performance envelope and to compare different hull designs. Exceeding hull speed is possible but typically inefficient for displacement hulls.

Yes — planing hulls and semi-displacement hulls can exceed hull speed by rising up on top of the water rather than pushing through it. Displacement hulls can also technically exceed hull speed with enough power, but the energy required increases dramatically. Catamarans and other slender multi-hulls often have a high length-to-beam ratio that allows them to push past the theoretical limit more efficiently.

Since hull speed depends solely on waterline length, the only way to increase it without modifying the hull shape is to increase the effective waterline length — for example by trimming the boat bow-down so more of the hull contacts the water. Adding ballast or weight distribution changes can have a small effect, but structural hull changes yield the most significant gains.

The standard hull speed formula applies less reliably to catamarans and other multihulls. Their narrow, slender hulls have a high length-to-beam ratio that reduces wave-making resistance, allowing them to sail faster than the formula predicts. As a result, performance catamarans routinely exceed their theoretical hull speed.

A displacement hull travels through the water, supported entirely by buoyancy. It pushes water aside as it moves, creating a bow wave whose wavelength limits speed. A planing hull, at higher speeds, rises up and skims across the water's surface, greatly reducing drag and allowing much higher speeds. Hull speed only constrains displacement hulls.

The formula V = 1.34 × √LWL is a useful approximation, not an exact physical law. The constant 1.34 can range from about 1.1 for full, beamy hulls to 1.5 or higher for very slender or lightweight designs. It provides a reliable rule-of-thumb for typical monohull sailboat and powerboat design, but should be treated as a guide rather than a precise limit.