Navigation Calculators

Distances, bearings, dead reckoning and course correction. 12 calculators usable at sea, in the air or on land.

Great circle distance uses the Haversine formula, and the result surprises people looking at a flat map. The shortest path between London and Tokyo goes near the Arctic, not east across Asia, and it is around 1,500 km shorter than the rhumb line that looks straight on a Mercator projection. That is why long-haul flight paths bend north, and why a rhumb line course, which the site also provides, is a different and usually longer route that has the advantage of a constant compass bearing.

Magnetic declination is the correction between true and magnetic north, and it is not a constant. It varies by location, and it drifts year on year as the magnetic pole moves, which has been unusually fast this century. A chart’s printed declination comes with a date and an annual change rate for exactly that reason. Using a 20 year old figure can put a long leg well off.

Anchor scope works from depth plus tidal range plus bow height, not depth alone. Anchoring to a scope calculated at low water is how boats drag on the flood.