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.

Compass heading (°)

Compass heading by the ship's compass.

North deviation (°)

Deviation recorded on north; positive east, negative west.

East deviation (°)

Deviation recorded on east; positive east, negative west.

South deviation (°)

Deviation recorded on south; positive east, negative west.

West deviation (°)

Deviation recorded on west; positive east, negative west.

Interpolate magnetic compass deviation between a vessel's cardinal calibration values. The defaults reproduce the included example card and should be replaced with the vessel's own swing data. 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]

Deviation (°)

Positive east, negative west deviation.

• 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.

• Shift Rate Calculator

  Compute the signed rate of the shortest compass-direction change between two mean wind headings, correctly handling the wrap across north.

• Oscillation Amplitude

  Compute half the shortest circular separation between the two extreme compass headings, including oscillations that cross north.

• 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.