The ETA (estimated time of arrival) follows from distance, speed and departure time — it sounds simple, but it decides harbour approaches, lock times and tidal windows. This guide shows how to plan it realistically in NauticCalc and align it with the tides.
Prerequisites
- Distance in nautical miles (nm)
- Realistic speed in knots (kn) — an experience value rather than a wish value
- Departure time (local)
Step 1: Determine the distance
Take the nm for the leg from the chart, plotter or log. On coastal passages you sum the waypoints instead of measuring in a straight line — detours around shoals and restricted areas count.
Step 2: ETA calculator
Open the ETA calculator and enter nm, kn and the departure. Use a realistic average for the speed, not a peak value — calms and manoeuvres pull the average down.
Step 3: Interpret the result
The app gives passage time and ETA. Plan a margin for current, wind and manoeuvres (harbour, locks). An arrival just before dark or low water is a reason to leave earlier or adjust the passage.
Step 4: Align with the tides
For the harbour entry, check the time window via the Tides and, if needed, the WorldTides key. That way the ETA does not land in the middle of low water or the strongest foul current.
Common mistakes
- Using a wish speed instead of a realistic average
- Planning no margin for current, wind and manoeuvres
- Measuring the straight-line distance instead of the actual waypoint distance
- Not aligning the ETA with tide/daylight
Read next: Blog: calculating ETA · ETA feature