A watertight bulkhead is a transverse bulkhead mounted on the tank top and it must extend right to the uppermost continuous deck.
Watertight bulkheads are installed to:
- Divide the ship into watertight compartments and thereby limit flooding if the hull plating is damaged;
- Improve the transverse strength of the structure;
- Prevent distortion of the hull plating;
- Support the deck girders and longitudinals;
- Rigidly attach the tank top to the upper deck;
- Greatly slow the spread of fire.
The number and location of watertight bulkheads on a ship depend on the length and type of ship and the location of the machinery space. The SOLAS Convention determines the number and location of these bulkheads. But in general, there is a watertight bulkhead (collision bulkhead) at the bow that should be located between 0.05L and 0.075L (L = length between perpendiculars of a ship), a watertight bulkhead at the stern that should form a watertight aft compartment (after peak) that encloses the stern tube, and a watertight bulkhead at each end of the machinery space (where the aft bulkhead may be the after-peak bulkhead).
All members that pass through a watertight bulkhead, such as ventilation ducts, piping and electric wiring, must be mounted so as to maintain the watertight integrity of the bulkhead. That is why remote controlled stopcocks are generally found on certain pipes that pass through watertight bulkheads.
