All ships go to drydock for regular cleaning and repairing and painting. This is what happens: The ship noses into a place surrounded by three concrete walls. Huge water-tight gates swing shut behind her, penning her in. Mooring lines hold her steady in the exact center of the dock, and pumps go to work taking out all the water in which she floats. Slowly the ship settles into a sort of cradle that has been prepared on the floor of the dock to fit her hull just right. When the water is all out, there she stands, balanced and braced. Now men can work under her and all over her—and inside. They scrape off the barnacles, paint the hull, and repair any parts that have begun to wear out. To reach some parts of the hull painters use long-handled brushes—really long. They’re often three times as tall as a man!

Experts go over the ship as carefully as doctors examine people. But many men work at top speed in shifts around the clock, and a ship often spends only twenty-four hours in drydock. Then the gates open. Water flows back into the dock. The ship floats again, ready to go to sea.

Sometimes a ship can’t get to drydock. Then a floating drydock comes to the ship. It works the same way as a regular one. Floating drydocks have traveled to distant parts of the world, pulled by seagoing tugs.