Kayak Hull Speed Calculator

Hull speed is the theoretical maximum speed of a displacement hull, the point at which the bow wave becomes as long as the waterline and the hull is effectively trapped between its own waves, requiring exponentially more power to go faster.

The formula is: Hull speed (knots) = 1.34 × √(LWL in feet)

Or in metric: Hull speed (km/h) = 4.50 × √(LWL in meters)

Where LWL is the waterline length of the hull.

This explains why longer kayaks are faster: a 5-meter kayak has a hull speed of ~10.1 km/h, while a 4-meter kayak tops out at ~9.0 km/h. The longer boat requires much less paddling effort to cruise near its hull speed.

Practical kayak hull speeds:

• 2.5 m (8 ft) play boat: 7.1 km/h (3.8 kts)
• 3.7 m (12 ft) recreational: 8.7 km/h (4.7 kts)
• 4.6 m (15 ft) touring: 9.7 km/h (5.2 kts)
• 5.5 m (18 ft) sea kayak: 10.6 km/h (5.7 kts)
• 6.1 m (20 ft) racing kayak: 11.1 km/h (6.0 kts)

Can you exceed hull speed? Narrow, light kayaks (especially racing designs) can be paddled slightly faster than theoretical hull speed because their fine entry allows the bow wave to extend. Racing kayaks can sprint 2-3 km/h above their theoretical hull speed.

Surf skis sit on top of waves rather than displacing water, bypassing hull speed limitations entirely when surfing. Speeds of 20+ km/h are possible in good conditions.

The catch, and it is a big one for short boats. Hull speed is a wave-making limit borrowed from displacement sailboat design, and it assumes you have the power to reach it. A sailboat usually does. A paddler often does not.

Look at the top of the table above. A 2.5 m playboat has a “hull speed” of 7.1 km/h, but nobody paddles a playboat at 7.1 km/h. Short, wide, high-rocker whitewater hulls are dominated by form drag long before wave-making becomes the limiting factor, and a strong paddler in one will struggle past about 5 km/h on flat water. The number is arithmetically correct and practically meaningless at that end of the range.

The formula earns its keep for long, narrow boats, where wave-making really is what stops you: a 5.5 m sea kayak’s 10.6 km/h is a genuine ceiling that a fit paddler can approach in a sprint. Below roughly 4 m, treat the result as trivia rather than a target.

For trip planning in a touring or sea kayak, assume you will cruise at 60-75% of hull speed with comfortable effort, and 80-90% with hard paddling. In a recreational or whitewater boat, ignore the percentage and use a real cruising figure instead: 4 to 5 km/h is honest for most people.