How far away can a ship be seen across an ocean?
The distance that you can see an object on the horizon depends partly on the height of your eye. So – although we don’t recommend it – if you’re an average-sized adult and you stood up in a row boat on the ocean, you should be able to see the horizon line about three miles away. That’s assuming you have perfect weather conditions. If you sit down, your horizon suddenly comes a mile or so closer in. Now suppose there’s a ship in the view. If a ship moves away from you toward the horizon line, you can indeed watch it disappear over the curve of the Earth. How far away the ship can get until you lose sight of it depends partly, again, on how high up your eyes are – and partly on how tall the ship is. Let’s consider a standard-sized sailing ship – say, about 24 feet tall. With conditions of perfect visibility, you should see the tip of the ship’s mast disappear when the ship is nearly nine miles away.
