Calculating passage time, arrival, current and night passages
Calculating your arrival is simple: distance divided by speed over ground gives the passage time;
a foul current comes off your speed, not off the distance.
Calculator
Two knots of foul current cost you more than an hour over forty nautical miles at ten knots through the water. Work from the log distance instead of speed over ground and you make port after dark. Every passage plan therefore has to answer when darkness falls and whether you can still enter the destination harbour at that hour.
Some policy wordings restrict night passages, for instance as a condition on where the boat is kept. Theft happens at night, and collisions happen in poor visibility.
Night hours matter mainly for jet skis: some policies contain a night clause, for example between 22:00 and 08:00, so check the wording. For boats and yachts there is no night clause; hull cover applies around the clock in every tariff. What remains is seamanship: the prescribed navigation lights, an attentive lookout and a speed to suit the conditions.
Frequently asked questions
Do boat policies have a night clause?
Only for the jetski.
Some jet ski policies contain one, for example between 22:00 and 08:00; check your wording.
For boats and yachts there is no night clause.
How do I allow for current?
Take a foul current off your speed and add a fair one; the distance stays the same,
but it is your speed over ground that changes.
Worked out for your type of boat
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