Sailing Passage Planner (Distance, Tacking, Speed, ETA, Daylight Arrival & Fuel)
Plan a coastal or offshore passage: effective distance with the upwind legs tacked out, realistic average speed against hull speed and current, hours and ETA from your departure time, whether you arrive in daylight, engine hours and fuel with reserve, and a watch rota for the crew.
How it works
effective distance = D × (1 − upwind share) + D × upwind share ÷ cos(tacking angle ÷ 2) · average SOG = 1 ÷ [(sail time share ÷ sail SOG) + (motor share ÷ motor SOG)] · hours = distance ÷ SOG; ETA = departure + hours · fuel = motoring hours × burn × 1.3 reserve · hull speed = 1.34 × √LWL
Passage time is the sum of honest numbers: the miles you will actually sail (upwind legs are 40% longer at a 90° tacking angle), an average speed that is well below hull speed once light patches and reefed nights are counted, the current, and the share of the trip you will motor. From that fall the arrival time — which matters, because entering an unfamiliar harbour in the dark is the classic avoidable mistake — the fuel to carry with a reserve, and the watch system that keeps the crew rested. Use the calculator as a check on the plan, then update it with real speeds as the passage unfolds.
Worked example
A 180 nm passage with 30% of it dead upwind at a 90° tacking angle is really about 202 nm. Averaging 5.5 knots sailing and 6 motoring for a quarter of the time gives 5.6 knots over the ground and about 36 hours; leaving at 06:00 the ETA is about 18:00 on day 2, in daylight, after one night at sea. Nine hours of engine at 3.5 L/h uses about 32 L — carry at least 41 L, well within a 150 L tank whose motoring range is about 257 nm. Three crew run a 3-on/6-off rota.
Frequently asked questions
What average speed should I plan on?
Take your boat's comfortable cruising speed in a good breeze and multiply by about 0.75 for a 24-hour average — a 30 ft waterline boat that does 7 knots on a reach averages 5–5.5 over a passage. Plan pessimistically and be pleasantly early; the daylight-arrival check tells you if being early is a problem.
How much fuel reserve?
The rule of thirds: a third out, a third back, a third in reserve — for a one-way passage, plan to arrive with at least 25–30% of the fuel you expected to use still in the tank, more if the destination fuel dock is uncertain or the forecast is for calms.
How do I avoid a night arrival?
Adjust the departure time first (leaving after dark is much easier than arriving in it), then slow down late in the passage — heave-to or stand off — rather than pressing on. Many cruisers time departures so the ETA lands mid-morning, giving a margin for both faster and slower passages.
Related calculators
Boating figures are planning estimates based on published rules of thumb and standards (USCG, ABYC, manufacturer tables). Your boat's capacity plate, builder documentation and local regulations govern; conditions at sea vary.