Hull Speed Calculator
Calculate maximum displacement speed
📐 Formula Used
Hull Speed = 1.34 × √LWL
Where LWL is waterline length in feet. This formula gives the theoretical maximum efficient speed for displacement hulls before wave resistance dramatically increases.
What is Hull Speed?
- ⚓ Hull speed is the speed at which a displacement vessel’s bow wave wavelength equals its waterline length
- 📈 Above hull speed, power required to go faster increases dramatically
- ⛵ Applies to sailboats, trawlers, and displacement cruisers
- 🚤 Planing hulls can exceed hull speed by rising onto plane
Our hull speed calculator helps you find the maximum velocity your boat can reach without planing. This simple tool applies the hull speed formula to calculate your vessel’s theoretical limit based on design. Enter your boat’s waterline length to begin understanding how physics create a natural speed barrier for any ship that moves through rather than over the water.
What Is Hull Speed?
Hull speed is the speed at which a displacement hull produces a bow wave equal in height to the vessel length. As the bow wave’s wavelength increases, the stern drops into a trough. To go faster, the craft must climb its own wave — demanding exponentially more power and energy. This explain why a boat with longer waterline length can reach higher velocities efficiently. Every foot of additional length allows the vessel to travel at greater speeds before hitting this threshold.
The Formula: 1.34 × √Waterline Length (feet) = Hull Speed in knots
How to Calculate Hull Speed
Measure Your Boat
Find your waterline length — the row from bow to back
Input the Value
Enter the measurement and select your preferred unit
Get Results
See displacement speed instantly with accurate hull speed calculation
Hull Speed by Boat Length
| Waterline | Hull Speed | Example |
|---|---|---|
| 25 ft | 6.7 knot | Daysailer |
| 36 ft | 8.0 | Cruiser |
| 49 ft | 9.4 | Trawler |
Displacement vs Top Speed
A displacement hull pushes medium aside as it moves. The wave pattern determines how efficiently your boat can operate. Near hull speed, fuel economy remains optimal for any voyage. Attempting to break past this limit is possible but impractical — consumption figures rise dramatically for minimal gains in velocity.
Planing craft can soar above their bow wave and achieve much greater velocities. But traditional displacement configurations — from sailing yachts to trawlers — operate best at or below their calculated threshold, which is why our calculator matters for realistic planning and performance expectations. The stern region remains in the trough at optimal cruising conditions.
Why This Calculator Matters
- Fuel efficiency — operating near hull speed maximizes range
- Voyage planning — understand realistic journey times accurately
- Vessel selection — evaluate performance potential before purchasing a new boat
- Engine sizing — match your hull appropriately for optimal results
FAQs
Can a boat exceed hull speed?
Yes, but wave resistance grows sharply as you approach that threshold. Displacement hull speed is the speed at which efficiency drops — not an absolute ceiling. Going beyond requires enormous fuel and thrust, making it impractical for most vessels. Fast planing boats escape this entirely by riding on the surface.
Does hull speed apply to all boats?
Only to traditional non-planing vessels. Planing boats can escape wave resistance by riding above rather than pushing through it, allowing them to exceed these calculated thresholds completely.