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

Radius (NM)

Required number in NM. Radius of the circular search area.

Sector angle (°)

Optional number in °. Angle between successive search legs.

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

Calculate the chord between successive radials of a sector search pattern as twice the radius times the sine of half the sector angle. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Chord length (NM)

Returned number in NM. Straight line distance crossed on each leg.

• 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.
• Sector angle must be at least 30.
• Sector angle must be no greater than 120.
• 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.

• 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.

• Search Pattern Area

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