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

Distance run (NM)

Required number in NM. Distance sailed since the last fix.

Compass error (°)

Optional number in °. Assumed steering or deviation error of the compass.

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

Estimate the radius of the position error circle from a compass steering error as distance run times the error in degrees divided by fifty seven point three. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Error circle radius (NM)

Returned number in NM. Radius of the circle containing the probable position.

• 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.
• Compass error must be at least 0.
• Compass error must be no greater than 10.
• 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.

• AIS Range Estimate

  Estimate the range at which an automatic identification system target is received as one point one seven times the sum of the square roots of the own and target antenna heights in feet.

• Cross Track Error Calculator

  Calculate the signed perpendicular distance from a desired course given distance run and the bearing back to the start point.

• Horizon Distance Calculator

  Compute the distance to the visible horizon in nautical miles as the coefficient one point one seven times the square root of eye height in feet.