Allan Wayne Harrison, age 9, of Gastonia, N.C., for his question:

HOW DOES THE DRY DOCK WORK?

A dry dock is an area where a ship can lie out of the water while repairs are being made below its water line.

The most common dry dock looks very much like a large concrete bathtub sunk into the ground near aharbor or other waterway. The dock area is filled with water with one end going to the waterway. A vessel then enters the dock and shipyard workers place a huge floating or sliding gate against the open end. Pumps then remove the water until the ship's bottom comes to rest on wooden blocks placed on the floor of the dock. Long pieces of wood are wedged between the ship and the sides of the dock to help support it.

After the repair work is completed, workers flood the dry dock with water until the vessel is again floating. The gate is then opened and the ship sails out.