🚤 Hull Speed Calculator
Calculate theoretical hull speed and analyze displacement hull performance limits.
Understanding Hull Speed
What is Hull Speed?
Hull speed is the theoretical maximum speed of a displacement hull, occurring when the bow and stern waves created by the boat merge into a single wave system. At this speed, the boat sits in the trough between its bow and stern waves.
The Hull Speed Formula
Hull Speed (knots) = 1.34 × √(LWL in feet)
This formula, derived from wave theory, shows that longer boats have higher hull speeds. Doubling the waterline length increases hull speed by about 41%.
Speed/Length Ratios
- < 1.0: Slow cruising, very efficient
- 1.0-1.2: Normal cruising speed
- 1.2-1.34: Fast cruising, approaching hull speed
- 1.34: Theoretical hull speed
- > 1.34: Exceeding hull speed (requires exponentially more power)
Breaking the Hull Speed Barrier
While displacement hulls struggle to exceed hull speed efficiently, it's possible with enough power. However, fuel consumption increases dramatically. Light, flat-bottomed boats can transition to planing mode and exceed hull speed more easily.
Frequently Asked Questions
Can sailboats exceed hull speed?
Yes, sailboats can exceed hull speed when surfing down waves or with sufficient sail power in strong winds. Light, flat-hulled boats and multihulls can exceed hull speed more easily than heavy displacement boats. Racing boats regularly sail at 1.5-2.0 times hull speed.
Why is hull speed important for cruising?
Hull speed helps you plan realistic passage times and fuel consumption. Most cruising sailboats motor at 0.9-1.0 times hull speed for efficiency. Trying to exceed hull speed under power wastes fuel with minimal speed gain. Understanding your hull speed helps set realistic expectations for boat performance.