Boat Speed Calculator – Calculate Maximum Hull Speed for Any Boat
Find your boat's theoretical maximum hull speed with our Boat Speed Calculator. Enter waterline length to calculate hull speed in knots, mph, and km/h — essential knowledge for sailors and powerboat operators planning passages.
Length at waterline, not overall length (LOA)
Typical LWL Examples:
- • Small sailboat (25'): ~22' LWL
- • Cruiser (35'): ~28' LWL
- • Large yacht (50'): ~40' LWL
Hull Speed Results
Enter waterline length and click Calculate to see hull speed
Understanding Hull Speed
Hull speed is the theoretical maximum efficient speed for displacement hulls:
- Formula: Hull Speed (knots) = 1.34 × √LWL (feet)
- Physics: Boat creates bow and stern waves; at hull speed, wavelength equals waterline length
- Beyond hull speed: Boat must climb its own bow wave, requiring exponentially more power
- Planing hulls: Can exceed hull speed by rising onto water surface
Note: Some modern designs with fine entries can exceed traditional hull speed. The 1.34 factor varies with hull shape (1.2-1.5).
How It Works
Enter your boat's waterline length
Measure the length where the hull meets the water surface, not the overall boat length.
Select your hull type
Choose between displacement, semi-displacement, or planing hull based on your boat design.
Get your hull speed instantly
See maximum efficient speed in knots, mph, and km/h with tailored recommendations.
Key Features
Multiple Hull Types
Supports displacement, semi-displacement, and planing hull calculations.
Unit Conversion
Results displayed in knots, mph, and km/h for easy reference.
Planing Speed Estimate
Calculates the speed threshold where planing hulls rise onto the water surface.
Smart Recommendations
Get tailored advice based on your hull type and calculated speed.
Hull Speed by Boat Type Reference
| Boat Type | Typical LWL | Hull Speed |
|---|---|---|
| Small Sailboat | 20-25 ft | 6.0-6.7 knots |
| Cruising Sailboat | 28-35 ft | 7.1-7.9 knots |
| Large Yacht | 40-50 ft | 8.5-9.5 knots |
| Trawler | 30-45 ft | 7.3-9.0 knots |
| Motor Yacht | 35-60 ft | 7.9-10.4 knots |
Frequently Asked Questions
What is hull speed and why does it matter?
Hull speed is the theoretical maximum efficient speed for displacement hulls. Beyond this speed, resistance increases dramatically, requiring exponentially more power and fuel.
Can a boat go faster than hull speed?
Displacement hulls cannot efficiently exceed hull speed. Planing hulls can exceed it by rising onto the water surface, but this requires significantly more power.
What is the 1.34 factor in the hull speed formula?
The 1.34 factor is derived from wave physics and represents the speed-length ratio for typical displacement hulls. It can range from 1.2 to 1.5 depending on hull shape.
How do I measure waterline length accurately?
Measure the length of the hull at the water surface when the boat is loaded normally. This is typically shorter than the overall length (LOA) due to bow and stern overhangs.
What hull speed should I cruise at for fuel efficiency?
For displacement hulls, cruising at 70-85% of hull speed offers the best fuel efficiency. Pushing beyond 90% dramatically increases fuel consumption.
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