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.

Search radius (NM)

Radius of the area to sweep around the datum.

Determine the first leg length of an expanding square search pattern so the squared spiral reaches the requested search radius after two legs from the datum. 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]

First leg length (NM)

Length of the first leg leaving the datum.

• 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.

• Sector Search Leg Length

  Calculate the chord between successive radials of a sector search pattern as twice the radius times the sine of half the sector angle.

• Search Pattern Area

  Calculate the area swept by a square search pattern as the square of its side length.

• Anchor Circle Radius Calculator

  Estimate the maximum anchor-to-bow radius from water depth and rode scope. Add the vessel length when checking the full area swept by the stern.