Depending on length, your boat should have at least four watertight bulkheads, with watertight doors. This is the lesson learned from Titanic. Titanic’sSecond bulkheads stopped short of the deck. When one compartment filled with water, it slopped over into the next. This was fixed in Britannica’s design, but all the doors and port lights were open when she struck the mine. Ever since Titanic, all ships have had watertight bulkheads, most with manual and automatic means of closure on any openings.

The four bulkheads are arranged as follows. There should be an aft bulkhead, at a distance from the stern of 5-8%percent of the boat length, a collision bulkhead (doubling as a chain locker) in the forepeak, and two other bulkheads in between. The space in the stern can be filled with polyurethane foam. Ideally, none of these bulkheads should have doors in them. They should be entered through deck-level hatches. But from a practical standpoint, doors are unavoidable. Any doors in bulkheads should be watertight. The engine-room door should have a fire-proof view port, so you can peek before charging in.

Make sure bulkheads cannot be breached by back-pressure through the plumbing system.

Bulkheads should be isolated acoustically.