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.

Distance to mark (nm)

Distance from the boat to the mark.

Understand (°)

Angle by which the layline is undershot.

Tacking angle (°)

True wind angle sailed when beating.

Compute the distance gained by footing below the layline from the distance to the mark, understand angle, and tacking angle. 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]

Understand distance (nm)

Distance gained by understanding the mark.

• 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.

• Overstand Distance Calculator

  Compute the extra distance sailed when overstanding the mark from the distance to the mark, overstand angle, and tacking angle.

• Layline Distance Calculator

  Compute the distance along a layline to the mark given the lateral offset and tack angle.

• Distance to Layline Calculator

  Calculate the distance along the course centerline to a layline from the lateral offset and half of the total angle between port and starboard tacks.