The engine turns a drive shaft with a propeller. The water moves through the propeller like air moves through a fan, causing the boat to move forward. As the speed increases, the hull of the boat rises higher in the water reducing the friction. That allows the boat to go even faster. The airfoil design of a speedboat is important because once the speed gets high enough, the boat is essentially flying. The challenge for the operator in a race is to maximize the speed without allowing it to rise out of the water enough for the air under it to flip it over on it's back.
Answered Oct 08, 2012
Edited Oct 08, 2012