Watertight Bulkhead is an integral part of the modern ship construction and serves as a strengthening member. It is to be noted that it also gives protection to the ship from any kind of fire or grounding. It won’t let the other compartment fill in case grounding takes places in one part.
To simplify this, consider you have a box of rectangular size. Now when you put this box in water, there will be racking stress which will push the side plates inside. But if you divide the box transversely, by adding plates, not only they give strength but also prevents from flooding other spaces if there is a breach of hull. Also same goes with the fire. Here in this post we will understand the requirements of watertight bulkheads and also how they are made when it comes to construction.
Watertight Bulkheads Regulations
1) A forward or COLLISION bulkhead to be present not less than 5 % of the ship length and not more than 8%.
2) One bulkhead forward and aft of machinery space.
3) A water tight bulkhead to enclose the shaft cooling tank or called as stern tube cooling tank.
For passenger ships, in addition to the above regulations, several other sub watertight bulkheads to be constructed considering the permeability of each main water tight bulkhead.
Note: Above minimum standards are for ship of length till 90 meters. Ships having length needs to be divided in more water tight bulkheads.
Watertight Bulkheads Construction
For collision bulkhead, it should reach till freeboard deck. While the aft bulkhead can reach till upper or 2nd deck and not need to extend to freeboard. Other bulkhead should reach till the flat deck (used for walking).
The plating for the bulkhead fitted is very important. The side frame is removed and the bulkhead plating is fitted at that position. The thickness of the plate is more at the bottom than at top and gradually increases from bottom to top. This is done to give strength at the top.
Since simple plating of bulkhead is of no use. It needs to be strengthened. Bulkhead stiffeners are used to strengthen the bulkhead. They are fitted 75 centimeters apart and 60 centimeters apart in collision bulkhead.Stiffeners can be of any type like angles, bulb angles etc. They are welded at the bottom tank top to all the way up to the upper deck.
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Dry Cargo or tanker ships use corrugated bulkheads and they don’t need stiffeners for strengthening. Corrugation can be horizontal or vertical depending upon the construction. But longitudinal bulkheads always have horizontal corrugations. Below diagram shows a corrugated bulkhead.
Whenever there is a pipe passing through the watertight bulkhead, they are welded. Or the studs that join the piece are tightened to the plate by tapered threads. In no case pipes are joined by through holes, because if the bolts break, they will leave a clear hole leading to disturbing the water tight integrity.
Peak and aft collision bulkheads are tested by filling them till top of the water line or load line. While other bulkheads are tested by the pressurized hose sprayed over it. This was all from this article on water tight bulkheads. Hope you enjoyed reading every bit of it.
