Leeway Calculator
Calculate the effect of sailing leeway on your actual course and determine the lateral distance your boat travels because of wind-induced sideways drift.
Leeway Results
What is leeway?
Leeway is the sideways movement of a boat caused mainly by wind pushing the vessel away from the direction its bow is pointing. A boat can therefore be heading in one direction while its actual track across the water is slightly different.
The leeway angle describes the difference between the boat's heading and its actual direction of travel through the water.
How is leeway calculated?
When the leeway angle and boat speed are known, the boat's velocity can be separated into forward and sideways components using basic trigonometry.
$$V_{forward} = V \times \cos(\theta)$$
$$V_{lateral} = V \times \sin(\theta)$$
$$D_{lateral} = D \times \sin(\theta)$$
- V: Boat speed through the water.
- θ: Leeway angle.
- Vforward: Component of boat speed in the intended direction.
- Vlateral: Sideways velocity caused by leeway.
- D: Distance traveled through the water.
- Dlateral: Estimated sideways displacement over that distance.
Why does leeway matter in sailing?
Leeway can cause a sailing boat to miss its intended track, particularly when sailing close-hauled in strong crosswinds. The effect becomes more important over longer distances because a small sideways angle can produce a significant lateral displacement.
Example of leeway
Suppose a boat is traveling at 6 knots with a 5° leeway angle. Its sideways velocity can be estimated as:
$$V_{lateral} = 6 \times \sin(5^\circ)$$
$$V_{lateral} \approx 0.52\ knots$$
This means that approximately 0.52 knots of the boat's velocity is directed sideways rather than directly along its intended heading.
What is the difference between leeway and current?
Leeway is the sideways movement of the boat relative to the surrounding water, primarily caused by wind acting on the hull and sails. Current moves the surrounding water itself relative to the Earth. In real navigation, both effects may need to be considered when determining the boat's actual track over the ground.
Is this calculator suitable for marine navigation?
This calculator provides a mathematical estimate based on the supplied leeway angle and boat speed. Actual leeway depends on factors such as wind strength, wind angle, hull design, keel type, sail trim, heel angle, loading, and sea state. For navigation, measured or experimentally determined leeway is generally more useful than relying on a single assumed angle.