Repairing a ship is a good deal easier when the vessel is in dry-dock. Out of the water, it is easier to spot cracks and loose boards and other problems with the hull, and offers the chance to clear out the accumulation of foul-smelling bilge that can be found in even the best-made ships. But Milliways has no dry-dock for a vessel the size of the Pearl, and that makes work on the hull rather difficult...but not impossible.

This line of thought would explain why Merriman is slowly walking around the perimeter of the ship, carefully examining the hull for cracks and holes near the water-line.

If the fact that he's walking on the surface of the water is at all out of the ordinary -- well, he doesn't seem to be troubled by it.