<P> kilometres from him, which comes to about 11.3 kilometres away . The ship is a further 8.7 km away . The height of a point on the ship that is just visible to the observer is given by: </P> <Dl> <Dd> h ≈ (8.7 3.57) 2 (\ displaystyle h \ approx \ left ((\ frac (8.7) (3.57)) \ right) ^ (2)) </Dd> </Dl> <Dd> h ≈ (8.7 3.57) 2 (\ displaystyle h \ approx \ left ((\ frac (8.7) (3.57)) \ right) ^ (2)) </Dd> <P> which comes to almost exactly six metres . The observer can therefore see that part of the ship that is more than six metres above the level of the water . The part of the ship that is below this height is hidden from him by the curvature of the Earth . In this situation, the ship is said to be hull - down . </P>

How far can you see into the horizon