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Water Tight Bulkheads and Doorson Ships: Construction and

Arrangement

• The Safety of any ship highly depends on its water tight integrity and structural strength. That is why ships are so heavily stiffened and strengthened to survive rough weather, accidental grounding, or collision.

• However, the structure of a ship can still get damaged, allowing water ingress and instability problem. If the water ingress is not constrained in time, the ship will capsize and sink. For this reason, water tight bulkheads are fitted on ships to avoid such situations.

What are Watertight Bulkheads?

• Watertight bulkheads are vertically designed watertight divisions/walls within the ship’s structure, starting from ship’s double bottom top until the upper main deck. The bulkheads avoid ingress of water in a compartment if the adjacent compartment is flooded due to damage in ship’s hull, structure etc.

• Bulkhead Types• Contruction of bulkheads mainly depend on the

utility and type of the ship.• 1) Based on integrity and strength, they are

classified mainly into following types:• Watertight • Non-watertight• Tank (Oiltight)• 2) Based on design, they are classified mainly into

following types:• Plain or Flat• Corrugated

Advantages of Watertight Bulkheads

• Subdivision: Divides the vessel into small compartments so that in case of flooding after a collision or grounding etc. the ingress of water will be restricted to a particular compartment. Prevents progressive flooding and ultimate foundering of the vessel.

• It helps in increasing the transverse strength of the ship which helps in reducing raking stresses, and are important in preserving the transverse shape of a vessel. These are important contributors to the strength of the hull girder. They resist the tendency to deform the shape of the shell. In the case of longitudinal bulkheads, they contribute to longitudinal strength of the hull.

• Help to spread hull stresses over larger areas.

• In the case of liquid carriers, the bulkheads divide the vessel into tanks and reduce free surface effects on stability. This is especially so in the case of longitudinal bulkheads in tankers. Also, when the vessel is in motion in seaway, liquid cargoes slosh in the tanks. The bulkheads reduce the damage which could be caused due to sloshing of cargo in an open unrestricted space.

• Fire division: In case of fire in a compartment, these bulkhead help to control the spread of fire to neighboring compartments. They are specially designed to withstand high temperatures for this purpose.

• In order to fulfill these functions, watertight bulkheads must extend from the bottom plating right up to the bulkhead deck (uppermost continuous deck). Some exceptions are allowed however. Bulkhead plating and stiffening scantlings are adjusted according to the construction rules.

Construction and Design of Watertight bulkhead

• The watertight bulkhead is made stronger and thicker than other bulkheads to sustain the water pressure in case of water ingress.

• They are large area bulkheads, incorporated with a number of strakes of plating, which are welded to the ship’s structure at side shell, tank top and deck.

• The plating is arranged horizontally and stiffening is done vertically.

• The thickness of water tight bulkhead increases towards the bottom as with increase in depth the pressure of the water increase. The horizontal plating’s(strake’s) thickness is gradually increased towards the bottom of the bulkhead.

• Strengthening is increased by vertical plate bulb stiffeners or toe angle bar, welded and spaced about 760 mm apart. The ends of bulkhead stiffeners are bracketed to the deck beams and tank top.

• The collision bulkheads are 12% thicker than other watertight bulkheads and stiffener spacing is reduced to 600 mm to give extra strength to sustain collision.

Arrangement of Watertight Bulkheads on Ships

• The minimum number of water tight bulkhead depends upon the length of the ship and the location of its machinery space. All sea going merchant ships must have at least following bulkheads:

• 1) Collision bulkhead placed at forward of the ship at 0.05L (L is length of the ship) and it should be continuous to upper deck.

• 2) An aft peak bulkhead which protects and encloses the stern tube and rudder trunk of the ship.

• 3) Bulkheads enclosing the engine room at each end(fore and aft) if the location of the engine room is at mid ship.

• If the engine room is located at the aft of the ship, the aft peak bulkhead forms the part of aft bulkhead of engine room. Hence only one bulkhead is required to be placed at fore part of the engine room, separating it from the cargo space.

• SOLAS CH2-1, Part B- 2 - Subdivision, watertight and weathertight integrity

• 9 Double bottoms in passenger ships and cargo ships other than tankers • 10 Construction of watertight bulkheads • 11 Initial testing of watertight bulkheads, etc • 12 Peak and machinery space bulkheads, shaft tunnels, etc • 13 Openings in watertight bulkheads below the bulkhead deck in passenger

ships • 13-1 Openings in watertight bulkheads and internal decks in cargo ships • 14 Passenger ships carrying goods vehicles and accompanying personnel • 15 Openings in the shell plating below the bulkhead deck of passenger ships

and the freeboard deck of cargo ships • 15-1 External openings in cargo ships • 16 Construction and initial tests of watertight doors, sidescuttles, etc • 16-1 Construction and initial tests of watertight decks, trunks, etc • 17 Internal watertight integrity of passenger ships above the bulkhead deck • 17-1 Integrity of the hull and superstructure, damage prevention and

control on ro—ro passenger ships

Definitions(Reg 2)• 14 Permeability of a space is the proportion o f the

immersed volume o f that space which can be occupied by water.

• 16 Weathertight means that in any sea conditions water will not penetrate into the ship.

• 17 Watertight means having scantlings and arrangements capable of preventing the passage of water in any direction under the head of water likely to occur in intact and damaged conditions. In the damaged condition, the head of water is to be considered in the worst situation at equilibrium, including intermediate stages of flooding.

• 19 Bulkhead deck in a passenger ship means the uppermost deck at any point in the subdivision length (Ls) to which the main bulkheads and the ship's shell are carried watertight and the lowermost deck from which passenger and crew evacuation will not be impeded by water in any stage of flooding for damage cases defined in regulation 8 and in part B - 2 of this chapter. The bulkhead deck may be a stepped deck. In a cargo ship the freeboard deck may be taken as the bulkhead deck.

• Margin Line. A line drawn parallel to the bulkhead deck at side lines and 76 millimeters (equivalent to 3 inches) below the upper surface of that deck. The term is used in connection with the method of subdividing merchant ships.

• Peak and machinery space bulkheads, shaft tunnels, etc.(Regulation 12)

• 1 A collision bulkhead shall be fitted which shall be watertight up to the bulkhead deck. This bulkhead shall be located at a distance from the forward perpendicular of not less than 0.05L or 10 m, whichever is the less, and, except as may be permitted by the Administration, not more than 0.08L or 0.05L + 3 m, whichever is the greater.

• 2 Where any part of the ship below the waterline extends forward of the forward perpendicular, e.g., a bulbous bow, the distances stipulated in paragraph 1 shall be measured from a point either:.1 at the mid-length of such extension;.2 at a distance 0.015L forward of the forward perpendicular; or.3 at a distance 3 m forward of the forward perpendicular,whichever gives the smallest measurement.

• 3 The bulkhead may have steps or recesses provided they are within the limits prescribed in paragraph 1 or 2.

• 4 No doors, manholes, access openings, ventilation ducts or any other openings shall be fitted in thecollision bulkhead below the bulkhead deck.

• 5.1 Except as provided in paragraph 5.2, the collision bulkhead may be pierced below the bulkhead deck by not more than one pipe for dealing with fluid in the forepeak tank, provided that the pipe is fitted with a screw-down valve capable of being operated from above the bulkhead deck, the valve chest being secured inside the forepeak to the collision bulkhead. The Administration may, however, authorize the fitting of this valve on the after side of the collision bulkhead provided that the valve is readily accessible under all service conditions and the space in which it is located is not a cargo space. All valves shall be of steel, bronze or other approved ductile material. Valves of ordinary cast iron or similar material are not acceptable.

• 5.2 If the forepeak is divided to hold two different kinds of liquids, the Administration may allow the collision bulkhead to be pierced below the bulkhead deck by two pipes, each of which is fitted as required by paragraph 5.1, provided the Administration is satisfied that there is no practical alternative to the fitting of such a second pipe and that, having regard to the additional subdivision provided in the forepeak, the safety of the ship is maintained.

• 6 Where a long forward superstructure is fitted, the collision bulkhead shall be extended weathertight to the deck next above the bulkhead deck. The extension need not be fitted directly above the bulkhead below provided it is located within the limits prescribed in paragraph 1 or 2 with the exception permitted by paragraph 7 and that the part of the deck which forms the step is made effectively weathertight. The extension shall be so arranged as to preclude the possibility of the bow door causing damage to it in the case of damage to, or detachment of, a bow door.

• 7 Where bow doors are fitted and a sloping loading ramp forms part of the extension of the collision bulkhead above the bulkhead deck, the ramp shall be weathertight over its complete length. In cargo ships the part of the ramp which is more than 2.3 m above the bulkhead deck may extend forward of the limit specified in paragraph 1 or 2. Ramps not meeting the above requirements shall be disregarded as an extension of the collision bulkhead.

• 8 The number of openings in the extension of the collision bulkhead above the freeboard deck shall be restricted to the minimum compatible with the design and normal operation of the ship. All such openings shall be capable of being closed weathertight.

• 9 Bulkheads shall be fitted separating the machinery space from cargo and accommodation spaces forward and aft and made watertight up to the bulkhead deck. In passenger ships an afterpeak bulkhead shall also be fitted and made watertight up to the bulkhead deck. The afterpeak bulkhead may, however, be stepped below the bulkhead deck, provided the degree of safety of the ship as regards subdivision is not thereby diminished.

• 10 In all cases, stern tubes shall be enclosed in watertight spaces of moderate volume. In passenger ships the stern gland shall be situated in a watertight shaft tunnel or other watertight space separate from the stern tube compartment and of such volume that, if flooded by leakage through the stern gland, the bulkhead deck will not be immersed. In cargo ships, other measures to minimize the danger of water penetrating into the ship in case of damage to stern tube arrangements may be taken at the discretion of the Administration.

• Regulation 10• Construction of watertight bulkheads• 1 Each watertight subdivision bulkhead, whether

transverse or longitudinal, shall be constructed having scantlings as specified in regulation 2.17. In all cases, watertight subdivision bulkheads shall be capable of supporting at least the pressure due to a head of water up to the bulkhead deck.

• 2 Steps and recesses in watertight bulkheads shall be as strong as the bulkhead at the place where each occurs.

• Regulation 11• Initial testing of watertight bulkheads, etc.• 1 Testing watertight spaces not intended to hold liquids and

cargo holds intended to hold ballast by filling them with water is not compulsory. When testing by filling with water is not carried out, a hose test shall be carried out where practicable. This test shall be carried out in the most advanced stage of the fitting out of the ship. Where a hose test is not practicable because of possible damage to machinery, electrical equipment insulation or outfitting items, it may be replaced by a careful visual examination of welded connections, supported where deemed necessary by means such as a dye penetrant test or an ultrasonic leak test or an equivalent test. In any case a thorough inspection of the watertight bulkheads shall be carried out.

• 2 The forepeak, double bottom (including duct keels) and inner skins shall be tested with water to a head corresponding to the requirements of regulation 10.1.

• 3 Tanks which are intended to hold liquids, and which form part of the watertight subdivision of the ship, shall be tested for tightness and structural strength with water to a head corresponding to its design pressure. The water head is in no case to be less than the top of the air pipes or to a level of 2.4 m above the top of the tank, whichever is the greater.

• 4 The tests referred to in paragraphs 2 and 3 are for the purpose of ensuring that the subdivision structural arrangements are watertight and are not to be regarded as a test of the fitness of any compartment for the storage of oil fuel or for other special purposes for which a test of a superior character may be required, depending on the height to which the liquid has access in the tank or its connections.