Estimated Time of Arrival

This formula calculates how long a voyage will take if you know the distance to travel and the vessel’s average speed over the ground. It works because time is the amount of distance covered divided by how fast that distance is being covered, so larger distances take longer and higher speeds reduce the travel time. In nautical work, speed is usually measured in knots, meaning nautical miles per hour, so the units match directly and the result comes out in hours.

Use this when planning passage times, estimating arrival times, or checking whether a route can be completed within a tide window or daylight period. It is also useful for rough navigation calculations when you know the distance between two points and the boat’s expected average speed.

• Using kilometres or miles instead of nautical miles without converting them first
• Forgetting that knots already mean nautical miles per hour, so no extra unit conversion is needed
• Mixing up speed over the ground with speed through the water when currents are significant