Use this sailing calculation as a planning or educational cross-check for navigation, wind and current, rig loads, stability, anchoring, tides, visibility, performance, or recovery under explicitly stated conditions.

Heel angle (°)

Heel angle to windward.

Boat speed (kt)

Boat speed through the water.

K factor

Empirical leeway coefficient depending on hull shape and keel.

Estimate leeway angle with the empirical relation leeway = K times heel divided by boat speed squared. Calibrate K for the hull, keel, and knot-based speed data in use. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Leeway angle (°)

Leeway angle between heading and track.

• Actual conditions change with vessel design and loading, sea state, wind, current, tide datum, weather, chart accuracy, equipment, crew, regulations, and safety margins. Simplified formulas do not replace seamanship, approved stability data, or current navigation information.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Cross-check official charts, tide and weather services, instrument data, vessel manuals, and collision regulations; maintain conservative margins and a safe alternative plan.

• Lee Bow Effect Calculator

  Project current onto the desired course as current speed times the cosine of the relative angle. This along-course proxy does not model the true lee-bow effect, which also depends on heading, boat speed, and apparent wind.

• Downwind VMG Calculator

  Compute downwind velocity made good as target boat speed times the absolute cosine of the true wind angle.

• Upwind VMG Calculator

  Compute upwind velocity made good as target boat speed times the cosine of the true wind angle.