Why units have their own rules on board
At sea you meet units that rarely go together ashore: nautical miles and knots, fathoms and feet for depth, Beaufort for wind. Whoever converts between them confidently avoids gross errors in distance, speed and water depth.
The most important conversions
- Nautical mile (nm): 1 nm = 1852 m = 1.852 km. It corresponds (approximately) to one minute of arc on a great circle — which is why navigation reckons in nautical miles.
- Knots (kn): 1 kn = 1 nm/h. Speed in knots and distance in nautical miles feed directly into the ETA calculation.
- Beaufort ↔ knots: the Beaufort scale describes wind strength in steps (0–12). It can be converted approximately into knots — useful for comparing forecasts (often in Bft) with instruments (often in kn).
- Depth: metres, fathoms (1 fathom = 1.8288 m) and feet (1 ft = 0.3048 m) — depending on the chart.
- Temperature: degrees Celsius and Fahrenheit, for air and water.
Where mistakes happen
- Nautical mile vs. statute mile: the statute mile (1609 m) is not the nautical mile. Confusing them means being off by about 15%.
- km/h instead of knots: a speed value without a unit is worthless — 6 kn is about 11 km/h.
- Chart datum and the unit of depth overlooked, especially on old or foreign charts.
- Taking Beaufort as exact: Bft is a step, not a precise value — the conversion is an approximation.
Offline and without retyping
You often need conversions quickly and without a signal. In NauticCalc the Nautical conversions are available offline; the values flow straight into other calculators such as ETA or course correction — without retyping tables. How this works independently of the network in general is described under Offline navigation. How to convert individual units step by step is shown in the Guide: Convert units.
Common mistakes
- Unit left off and guessed at later.
- Nautical mile and statute mile mixed up.
- Depth in fathoms read as metres.
- Beaufort treated as an exact knot value.
Conclusion
Nautical conversions are basic craft: nautical mile, knots, Beaufort, fathom, degree. Whoever keeps the units cleanly apart and converts instead of guessing in case of doubt navigates more precisely — and turns forecasts and instrument readings into one coherent picture.
Read more: Nautical conversions · ETA calculator · Offline at sea
