Use this sailing calculation for planning or education when the vessel, units, reference directions, environmental conditions, and assumptions are explicitly known.

Side length (NM)

Required number in NM. Side length of the square search pattern.

The cited overview of Navigation supplies background for the terminology and domain context used by this tool.^[1]

Calculate the area swept by a square search pattern as the square of its side length. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Pattern area (NM²)

Returned number in NM². Area covered by the square pattern.

• Vessel design and loading, sea state, wind, current, tide datum, weather, chart accuracy, equipment, crew, and safety margins can make real conditions differ from a simplified result.
• Use finite inputs in the displayed units, preserve source measurements and assumptions, and independently verify consequential decisions.

Cross-check current charts, tide and weather services, instrument data, vessel manuals, and applicable navigation rules, and retain a conservative alternative plan.

• Expanding Square Leg Length

  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.

• 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.

• 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.