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.

Current (kt)

Current strength at the casualty position.

Time in water (h)

Hours the person has been in the water.

Wind (kt)

Wind speed driving windage drift.

Windage coefficient

Fraction of the wind speed converted to drift per knot per hour.

Estimate how far an overboard crew member drifts as current speed times time in the water plus wind speed times time scaled by a one percent windage coefficient. 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]

Total drift (NM)

Total distance drifted from the falling-overboard point.

• 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.

• MOB Drift Distance

  Estimate the maximum down-drift distance when current and windage act in the same direction. Vector set and wind directions are required for a position estimate.

• 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.

• Mooring Windage Load Calculator

  Compute the wind load on a moored vessel from wind speed, windage area, and drag coefficient.