To check a hull for damage: look along the waterline in good lighting for gelcoat cracks, repair patches, or color inconsistencies (sign of past repairs). Tap along the hull with a plastic mallet or your knuckles — a hollow sound indicates delamination or voids. Check the keel and running surface on powerboats for impact damage. On trailered boats, look under the trailer bunks where impact damage is often hidden. A moisture meter used by a marine surveyor detects subsurface water intrusion invisible to the eye.
