Answer Construction Question 21

Question 21: With reference to collision bulkhead explain the following using sketches as required:

A. Purposes of collision bulkhead.

B. Construction of collision bulkhead.

C. Regulations governing the position and construction of such a bulkhead.

Answer: A. The purpose of the collision bulkhead is to protect the ship from sinking by complete loss of reserve buoyancy in the advent of a head-on collision. It also protects the holds and cargo positioned after of the bulkhead.

B. The number of bulkheads in a ship depends upon the length of the ship and the position of the machinery space. Each ship must have a collision bulkhead at least one twentieth of the ship's length from the forward perpendicular, which must be continuous up to the uppermost continuous deck. The stern tube must be enclosed in a watertight compartment formed by the stern-frame and the after peak bulkhead which may terminate at the first watertight deck above the waterline. A bulkhead must be fitted at each end of the machinery space although, if the engines are aft, the after peak forms the after boundary of the space. In certain ships this may result in the saving of one bulkhead. In ships more than 90 to in length, additional bulkheads are required, the number depending upon the length. Thus a ship 140 m long will require a total of 7 bulkheads if the machinery is amidships or 6 bulkheads if the machinery is aft, while a ship 180 m in length will require 9 or 8 bulkheads respectively. These bulkheads must extend to the freeboard deck and should preferably be equally spaced in the ship. It may be seen, that the holds are not usually of equal length. The bulkheads are fitted in separate sections between the tank top and the lowest deck, and in the 'tween decks'.

Watertight bulkheads are formed by plates which are attached to the shell, deck and tank top by welding. Since water pressure increases with the head, and the bulkhead is to be designed to withstand such a force, it may be expected that the plating on the lower part of the bulkhead is thicker than that at the top. The bulkheads are supported by vertical stiffeners spaced 760 mm apart. Any variation in this spacing results in variations in size of stiffeners and thickness of plating. The ends of the stiffeners are usually bracketed to the tank top and deck although in some cases the brackets are omitted, resulting in heavier stiffeners. The stiffeners are in the form of either bulb plates or toe welded angles. It is of interest to note that since a welded bulkhead is less liable to leak under load, or alternatively it may deflect further without leakage, the strength of the stiffeners may be reduced by 15%. It may be necessary to increase the strength of a stiffener which is attached to a longitudinal deck girder in order to carry the pillar load.
The bulkheads are tested for watertightness by hosing them using a pressure of 200 kN/m1.The test is carried out from the side on which the stiffeners are attached. It is essential that the structure should be maintained in a watertight condition. If it is found necessary to penetrate the bulkhead, precautions must be taken to ensure that the bulkhead remains watertight. The after engine room bulkhead is penetrated by the main shaft, which passes through a watertight gland, and by an opening leading to the shaft tunnel. This opening must be fitted with a sliding watertight door.

When pipes or electric cables pass through a bulkhead, the integrity of the bulkhead must be maintained.

C. Regulation regarding collision bulkhead are given in SOLAS-II-1 regulation 12.1
a. The bulkhead is watertight from the bottom of the ship, upto the main deck.
b. The collision bulkhead should be located within 0.05L or 10m whichever is less from the forward perpendicular.
c. No openings are allowed like doors, manholes, access openings, ventilation ducts etc.
d. Single pipe line is allowed to penetrated through the collision bulkhead for filling and emptying of fore peak tank.