The following problem was given to cadets at naval academy to have a check
on their knowledge of sea dynamics.
A ship is at anchor. Over the side hangs a rope ladder with rungs a foot apart.
The tide rises at the rate of eight inches an hour. At the end of six hours
how much of the ladder will remain above water when the tide begins to rise?
The answer is as follows. Since the ship's afloat, the water level in relation
to the ship stays the same. Therefore, eight feet are above water at the end
as at the beginning.