Converting nautical miles, cable lengths, fathoms and chart measurements

The nautical mile is not an arbitrary unit but one minute of arc on the globe. That is why you can measure distances directly on any chart, using the latitude scale. Cable lengths turn up in harbour information and fathoms for depths on older charts, and you still come across them on British and American charts today.

For insurance contracts, nautical miles are the language of cruising ranges. Limits are described in nautical miles from the coast, twelve-mile zones define coastal waters, and extensions of cover state radii in nautical miles around a given point. If you cannot convert the unit, you cannot check your cruising range.

That is more than theory: a passage that crosses the agreed limit is not covered. Our policy conditions allow a worldwide cruising range with no time limit and no geographical restriction, and anyone who chooses it need never do the sums. Where the range is limited, it is worth reading the exact wording before you cast off.