Outline: An Epic sea battle using surfboards

Divide the kids into teams:

U-Boats:
Paddle around with a ball shooting at cruisers. Board is inverted.

Crusiers:
Must avoid being sunk as long as possible. If the board is hit by a U-boat's ball, then the crew must abandon ship.

Lifeboat:
Paddles around looking for survivors in the water. Survivors must keep piling up on the lifeboat board. This gets very unstable and very funny.