On the subject of boats
There is a boat floating on a lake at low tide. There are 4 rungs of a ladder on the side visible above the water. They are all exactly 5 cm apart. At high tide, the water in the lake is 10 cm higher than at low tide. How many rungs are visible above the water at high tide?
This is a boat we're talking about.
What do boats do best?
Don't forget boats float.
4 still. Boats float, so no more rungs would go beneath the water.