Construction of bulkhead:
- Bulkheads are constructed of plates joined together and stiffened by vertical and horizontal stiffeners.
- As the water pressure increases with depth, the thickness of the plating in the lower part needs to be increased accordingly.
- The thickness of the plates used in the construction will also depend on the size of the stiffeners used to stiffen the bulkhead plating.
- In practice plate thickness could range from7mm at the top to 12 mm at the bottom.
- Plate bulkheads would usually be stiffened vertically with angle bars ,channels or offset bulb plates.
- Scantlings of stiffeners depend on the stiffener spacing and type of connection at the ends.
- Stiffeners are normally connected to the deck and bottom by welding directly or by a bracket.
- Separation between stiffeners is 750 -760 mm which can be increased if horizontal stringers are inserted between the vertical stiffeners.
- The plating of the bulkheads is connected to the surroundings plating-deck, ship’s side and tank top by welding after being double Veed at the edges.
- Modern Shipbuilding practice and technology enables more efficient corrugated bulkheads to be constructed.
- Because the plates are corrugated the bulkheads need not be fitted with stiffeners.
- Normally the corrugation is vertical or horizontal for transverse bulkheads and horizontal for longitudinal bulkheads.
- In areas where it is difficult to connect the corrugated bulkhead directly to the shell plating a flat plate with stiffening may be fitted at the sides.
- In order that watertight subdivision is continued below the level of the tank top the double bottom is fitted with a water tight floor.
- This floor must be as close to the watertight bulkhead above it.
- Bulkheads which form boundaries of oil carrying compartments will be of heavier scantlings ,the reason being that it may be necessary to carry a full tank cargo while the neighboring tank remains empty.
- Oil tightness must be guaranteed because often cargoes of different density/quality may be carried sharing the same separating bulkhead.
- Cargo contamination must not occur through leakage across the bulkhead.
- Adjacent tanks may be carrying water ballast.
- This must not get contaminated under any circumstances.
- In such case, precautions have to be taken to ensure water-tightness.
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Spacing and the number of bulkheads:
- The number of transvers bulkheads in a ship depends on her length and the position of the machinery space.
- The minimum bulkheads fitted on a ship are asf:
- The forward-most transverse water tight bulkhead is called collision bulkhead and is designed to protect the vessel in case of a collision .It is usually fitted between 5% of the length of the vessel(or 10 mtrs, whichever is less) and 8% of the length of the vessel from the forward perpendicular.
- In practice this bulkhead is placed as far forward as possible ( without violating the above requirements) so that as much cargo carrying space is available.
- The space forward of this bulkhead is the Fore Peak Tank,Abaft this bulkhead is the first hold or tank.
- The After Peak Bulkhead is situated aft and serves to enclose the stern tube in a watertight compartment.
- Other bulkheads are fitted on the forward and after sides of the machinery spaces .If the machinery space is aft ,then either the afterpeak bulkhead or the bulkhead abaft the machinery space can be dispensed with.
- The cargo spaces are also sub divided uniformly so that the vessel can survive being bilged anywhere along her length.
- Example a ship of 105 m shall have 5 or 6 bulkheads depending of position of machinery spaces.
- A ship of 145 m shall be fitted with 7 or 8 bulkheads.
- The sub division rules specify the separation and number of bulkheads to be fitted on a ship
Number Of Bulkheads(Cargo Ship)
|Length of Ship(Mtrs)/ Number Of Bulkheads||Midship M/S||Aft M/S|
- Some adjustment can be made to permit special requirements for example holds being sized to carry containers.
- Passenger ships which have to comply with SOLAS will have their case specially considered as flooding due to damages is to be controlled more stringently in such ships.