Hull Speed Calculator
Calculate theoretical hull speed for displacement boats and required waterline length
Calculate Hull Speed
Length of the hull at the waterline (load waterline length)
Hull Speed Results
Formula: Hull Speed (knots) = 1.34 × √(Waterline Length in feet)
Hull Speed Tips
Hull speed is theoretical maximum efficient speed
Loading boat heavier increases waterline length
Planing hulls can exceed hull speed efficiently
Longer, slender hulls can surpass theoretical hull speed
Example Hull Speeds
Small Sailboat (25 ft waterline)
Waterline Length: 25 feet
Formula: 1.34 × √25 = 1.34 × 5 = 6.7 knots
Hull Speed: 6.7 knots (7.7 mph, 12.4 km/h)
Boat Type: Day sailer, weekend cruiser
Medium Cruiser (35 ft waterline)
Waterline Length: 35 feet
Formula: 1.34 × √35 = 1.34 × 5.92 = 7.9 knots
Hull Speed: 7.9 knots (9.1 mph, 14.6 km/h)
Boat Type: Coastal cruiser, charter boat
Large Yacht (50 ft waterline)
Waterline Length: 50 feet
Formula: 1.34 × √50 = 1.34 × 7.07 = 9.5 knots
Hull Speed: 9.5 knots (10.9 mph, 17.6 km/h)
Boat Type: Ocean cruiser, racing yacht
Hull Types & Speed
Displacement Hull
Limited by hull speed formula
Semi-Displacement
Can exceed hull speed moderately
Planing Hull
Can greatly exceed hull speed
Multi-Hull
Slender hulls surpass formula
Sailing Performance Tips
Hull speed is most efficient speed for displacement hulls
Exceeding hull speed requires exponentially more power
Measure waterline length at normal load condition
Racing boats optimize length-to-displacement ratio
Wave conditions affect achievable speeds
Weight distribution affects waterline length
Understanding Hull Speed
What is Hull Speed?
Hull speed is the theoretical maximum speed a displacement hull can travel efficiently. At this speed, the boat's waterline length equals the wavelength of its bow wave, creating optimal wave interference patterns.
The Physics Behind It
As a displacement boat moves faster, it creates longer waves. When the wave length equals the waterline length, the bow and stern waves synchronize, allowing efficient movement. Beyond this speed, the boat tries to climb its own bow wave, requiring exponentially more power for small speed gains.
Hull Speed Formula
Hull Speed = 1.34 × √(Waterline Length)
Speed in knots, length in feet
Limitations & Exceptions
- •Modern hull designs can exceed theoretical hull speed
- •Planing hulls are not limited by this formula
- •Multi-hulls and ultra-light designs can surpass hull speed
- •Wave conditions and load affect actual achievable speeds