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.

Recognition angle (arcmin)

Angular size required to recognize the shape, rather than merely detect a point.

Shape size (m)

Linear size of the day shape such as the diameter of a ball or side of a diamond.

Calculate the distance at which a day shape subtends a chosen recognition angle. Weather, contrast, eyesight, and obstructions can reduce actual recognition range. 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]

Visibility range (NM)

Approximate range at which the day shape can be recognised.

• 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.

• Anderson Turn Course

  Calculate the return course reached by an Anderson turn, which rotates the heading two hundred forty degrees toward the chosen turn direction to bring the vessel back along its original track.

• 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.

• EPIRB Satellite Footprint Radius

  Calculate the geometric horizon footprint of an EPIRB search-and-rescue satellite from its orbital altitude. Actual detection also depends on the satellite network, beacon view, and link conditions.