A bulkhead is a wall inside the boat. Some only divide the cabins. Structural ones are bonded to the hull and deck and stiffen the whole shell. On many sailing yachts the main bulkhead also carries the chainplates, so the rig pulls on it every time the boat sails.
Bulkheads are usually plywood or a cored panel, bonded in with tabbing: strips of glass laid over the joint. Naval architect Dave Gerr notes that tabbing makes a secondary bond, which is never as strong as a primary one. Done well, with ground surfaces and filleted corners, it lasts. Done badly, flexing grows any crack until it lets go.
What a surveyor checks
Each bulkhead where it meets the hull and deck: tabbing lifted, cracked or hollow when tapped, and gaps at the joint. Then the signs of movement nearby, such as doors that bind or a chainplate bulkhead that shifts under rig load. Water stains and soft plywood at the foot of a bulkhead point to rot.
In the report
"Main bulkhead, starboard side, tabbing lifted along about 300 mm at the hull. Bulkhead firm. Grind back and retab." See loose bulkhead tabbing.