Arrive about 13:18
20 nautical miles, 4 h 3 min under way, plus 45 min stopped.
| Leg | Miles | Knots | Time | Leave | Arrive |
|---|---|---|---|---|---|
| Out of the harbour | 2 | 4 | 30 min | 08:30 | 09:00 |
| Across the bay | 14 | 5.5 | 2 h 33 min | 09:00 | 11:33 |
| Into the river | 4 | 4 | 1 h 0 min | 12:18 | 13:18 |
The speed is the one you expect to make through the water. Tide and wind will change what you make over the ground, and this sum leaves them out.
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How to use it
Put one leg on each line: a name if you like, the distance in nautical miles, the speed in knots, and the minutes you will stop at the end of it. A stop could be lunch, a lock, or waiting for the tide. Add the time you will leave. To see how fast you need to go, add the time you want to arrive by.
How it is worked out
A knot is one nautical mile an hour, so time is distance divided by speed. Twelve miles at 4 knots takes 3 hours. Each leg starts when the last one ended plus its stop. A trip that runs past midnight says "next day".
The speed needed is the total distance divided by the time you have, less the stops. If the stops alone take you past your time, the tool says so.
What it leaves out
This is the sum only. It doesn't know about tidal streams, wind, sea state or your route. Tidal streams and wind will change your speed over the ground, so plan with a tidal stream atlas and the forecast as well.
Sources
- BIPM, SI Brochure, Table 8: the knot is one nautical mile per hour, read 30 October 2026
Craig Fearn runs Still & Wake. He writes the guides and journal.