Bulkhead Information PDF

Bulkheads Bulkheads Vertical partitions in a ship arranged transversely or fore and aft are referred to as bulkheads. Those bulkheads which are of greatest importance are the main hull transverse and longitudinal bulkheads dividing the ship into several watertight compartments. Other li...

Bulkheads Bulkheads Vertical partitions in a ship arranged transversely or fore and aft are referred to as bulkheads. Those bulkheads which are of greatest importance are the main hull transverse and longitudinal bulkheads dividing the ship into several watertight compartments. Other lighter bulkheads, named ‘minor bulkheads’, which act as screens further subdividing compartments into small units of accommodation or stores, are of little structural importance. Watertight Bulkheads Transverse watertight bulkheads which divide a ship into a number of watertight compartments are important fpr the following reasons: 1. Strength: provide large structural support, resist any tendency to deformation (racking) and assist in spreading the hull stresses over a large area. 2. Fire: provides a very effective barrier to the spread of a hold or machinery space fire. 3. Subdivision: contains any flooding in the event of a compartment on one side of the bulkhead being bilged. Watertight Bulkheads As a rule the strength of the transverse watertight bulkheads is maintained to the strength deck which may be above the freeboard deck. Fire divisions Fire divisions “H” class divisions – Bulkheads and decks that are constructed of steel or other equivalent material, suitably stiffened, and are designed to withstand and prevent the passage of smoke and flame for the 120-minute duration of a hydrocarbon fire test. - “A” class divisions – Bulkheads and decks constructed of steel or other equivalent material, suitably stiffened, and designed to withstand and prevent the passage of smoke and flame for the duration of the one-hour standard fire test. - “B” class divisions – Bulkheads, decks, ceilings or linings that are designed to withstandand prevent the passage of flame for at least the first half hour of the standard fire test. - “C” class divisions – Divisions constructed of approved non- combustible materials. “A” class division There are 3 class of division :- 1. :- are those division formed by bulkheads and decks which comply with the following : They shall be constructed of steel or other equivalent material. They shall be suitable stiffened. They shall be so constructed as to capable of preventing the passage of smoke and flame to the end of the one-hour standard fire test. “A” class division They shall be insulated with approved non-combustible materials such that the average temperature of the unexposed side will not rise more than 140 degree celsius above the original temperature, nor will the temperature at any one point , Including any joint, rise more than 180 degree celsius above the original temperature within the time listed below: CLASS”A-60″ 60 MINUTES CLASS “A-30” 30 MINUTES CLASS “A-15” 15 MINUTES CLASS “A-0” O MINUTES “B” class division Are those division formed by bulkheads, decks , ceiling or lining which comply with following : They shall be so constructed as to be capable of preventing the passage of flame to the end of the first half hour of the standard fire test. “B” class division They shall have an insulation value such that the average temperature of the unexposed side will not rise more than 140 degree celsius above the original temperature, nor will the temperature at any one point, including any joint, rise more than 225 degree celsius above the original temperature within the temperature within the time listed below : CLASS “B-15” 15 MINUTES CLASS “B-0” 0 MINUTES “C” class division Are the divisions constructed of approved non combustible materials. They need meet neither requirements relative to the passage of smoke and flame or limitations relative to the temperature rise. Combustible veneers are permitted provided they meet the requirement. Spacing Of Watertight Bulkheads—cargo Ships The minimum number of transverse watertight bulkheads which must be fitted in a dry cargo ship are stipulated. A collision bulkhead must be fitted with: Collision bulkhead forward, An after peak bulkhead enclosing the stern tubes in a watertight compartment and A bulkhead at either end of the machinery space. Spacing Of Watertight Bulkheads—cargo Ships This implies that for a vessel with machinery amidships the minimum possible number of watertight bulkheads is four. With the machinery aft this minimum number may be reduced to three, the aft peak bulkhead being at the aft end of the machinery space. Collision Bulkhead Of these bulkheads perhaps the most important is the collision bulkhead forward. It is a fact that the bow of at least one out of two ships involved in a collision will be damaged. For this reason, a heavy bulkhead is specified and located so that it is not so far forward as to be damaged on impact. Neither should it be too far aft so that the compartment flooded forward causes excessive trim by the bow. Lloyd’s Register gives the location for ships whose length does not exceed 200 m as not less than 5 and not greater than 8 per cent of the ship’s length (Lloyd’s Length) from the fore end of the load waterline. Watertight Bulkheads As a rule, the collision bulkhead is fitted at the minimum distance to gain the maximum length for cargo stowage. The aft peak bulkhead is intended to enclose the stern tubes in a watertight compartment preventing any emergency from leakage where the propeller shafts pierce the hull. It is located well aft so that the peak when flooded would not cause excessive trim by the stern. Machinery bulkheads provide a self-contained compartment for engines and boilers preventing damage to these vital components of the ship by flooding in an adjacent hold. They also localize any fire originating in these spaces. Watertight Bulkheads The minimum number of watertight bulkheads will only be found in smaller cargo ships. As the size increases the classification society will recommend additional bulkheads, partly to provide greater transverse strength, and also to increase the amount of subdivision. These should be spaced at uniform intervals, but the shipowner may require for a certain trade a longer hold, which is permitted if additional approved transverse stiffening is provided. Watertight Bulkheads The following table indicates the number of watertight bulkheads recommended by Lloyd’s Register for any cargo ship. Watertight Bulkheads It is possible to dispense with one watertight bulkhead altogether, with the Classification society’s approval, if adequate approved structural compensation is introduced. In container ships the spacing is arranged to suit the standard length of containers carried. Watertight Bulkheads Each of the main watertight hold bulkheads may extend to the uppermost continuous deck; but in the case where the freeboard is measured from the second deck they need only be taken to that deck. The collision bulkhead extends to the uppermost continuous deck and the aft peak bulkhead may terminate at the first deck above the load waterline provided this is made watertight to the stern, or to a watertight transom floor. Watertight Bulkheads In the case of bulk carriers, a further consideration may come into the spacing of the watertight bulkheads where a shipowner desires to obtain a reduced freeboard. It is possible with bulk carriers to obtain a reduced freeboard under The International Load Line Convention 1966 if it is possible to flood one or more compartments without loss of the vessel. For obvious reasons, many shipowners will wish to obtain the maximum permissible draft for this type of vessel and the bulkhead spacing will be critical. Types of freeboards Freeboard Deck The freeboard deck is normally the uppermost complete deck exposed to weather and sea, which has permanent means of closing all openings in the weather part thereof, and below which all openings in the sides of the ship are fitted with permanent means of watertight closing. The freeboard deck is the deck below which all bulkheads are made watertight. Freeboard Deck Lower deck as a freeboard deck At the option of the owner and subject to the approval of the Administration, a lower deck may be designated as the freeboard deck provided it is a complete and permanent deck continuous in a fore and aft direction at least between the machinery space and peak bulkheads and continuous athwartships. Discontinuous freeboard deck, stepped freeboard deck Where a recess in the freeboard deck extends to the sides of the ship and is more than one metre in length, the lowest line of the exposed deck and the continuation of that line parallel to the upper part of the deck is taken as the freeboard deck Spacing Of Watertight Bulkheads - Passenger Ships Where a vessel requires a passenger certificate (carrying more than 12 passengers), it is necessary for that vessel to comply with the requirements of the International Convention on Safety of Life at Sea, 1974. Under this convention the subdivision of the passenger ship is strictly specified and controlled by the authorities of the maritime countries who are signatories to the convention. The calculations involved in passenger ship subdivision are based on the basic principle that watertight bulkheads should be so spaced that when the vessel receives reasonable damage, flooding is confined. No casualty will then result either from loss of transverse stability or excessive sinkage and trim. Construction Of Watertight Bulkheads Construction Of Watertight Bulkheads The plating of a flat transverse bulkhead is generally welded in horizontal strakes, and convenient two-dimensional units for prefabrication are formed. Smaller bulkheads may be erected as a single unit; larger bulkheads are in two or more units. Construction Of Watertight Bulkheads It has always been the practice to use horizontal strakes of plating since the plate thickness increases with depth below the top of the bulkhead. The reason for this is that the plate thickness is directly related to the pressure exerted by the head of water when a compartment on one side of the bulkhead is flooded. Construction Of Watertight Bulkheads Apart from the depth the plate thickness is also influenced by the supporting stiffener spacing. Vertical stiffeners are fitted to the transverse watertight bulkheads of a ship, the span being less in this direction and the stiffener therefore having less tendency to deflect under load. Construction Of Watertight Bulkheads Stiffening is usually in the form of welded inverted ordinary angle bars, or offset bulb plates, the size of the stiffener being dependent on the unsupported length, stiffener spacing, and rigidity of the end connections. Rigidity of the end connections will depend on the form of end connection, stiffeners in holds being bracketed or simply directly welded to the tank top or underside of deck, whilst upper tween stiffeners need not have any connection at all. Stiffeners Construction Of Watertight Bulkheads Vertical stiffeners may be supported by horizontal stringers permitting a reduction in the stiffener scantling because of the reduced span. Horizontal stringers are mostly found on those bulkheads forming the boundaries of a tank space. Swedged or Corrugated bulkheads Most modern ships used swedged or corrugated bulkheads. Both swedges and corrugations are arranged in the vertical direction like the stiffeners. Since the plating is swedged or corrugated prior to its installation, the bulkhead will be plated vertically with a uniform thickness equivalent to that required at the base of the bulkhead. This implies that the actual plating will be somewhat heavier than that for a conventional bulkhead, and this will largely offset any saving in weight gained by not fitting stiffeners. The swedges like the troughs of a corrugated bulkhead are spaced to provide sufficient rigidity to the plate bulkhead in order that conventional stiffeners may be dispensed with. Swedged Bulkheads Superstructure bulkheads are occasionally swedged, the spacing of the vertical swedges being similar to that of stiffeners. The swedges like the troughs of a corrugated bulkhead are spaced to provide sufficient rigidity to the plate bulkhead in order that conventional stiffeners may be dispensed with. Corrugated Bulkheads Corrugated plating is frequently used for bulkheads, mainly in tankers, bulk carriers and tank spaces of other ships. The corrugations are usually trapezoidal in shape and such bulkheads afford considerable savings in welding, are less susceptible to corrosion and provide easier tank cleaning and cargo flow. Corrugated Bulkheads Corrugated transverse bulkhead Corrugated Transverse Bulkhead on Bulk Carrier The bulkhead is constructed between lower and upper Stools. 1/23/2025 Ship Con 1&2 39 Boundaries of the bulkheads The boundaries of the bulkhead are double continuously fillet welded directly to the shell, decks, and tank top. Fitting of decks to a bulkhead A bulkhead may be erected in the vertical position prior to the fitting of decks during prefabrication on the berth. At the line of the tween decks a ‘shelf plate’ is fitted to the bulkhead and when erected the tween decks land on this plate which extends 300 to 400 mm from the bulkhead. The deck is lap welded to the shelf plate with an overlap of about 25 mm. Note The lap joint weld involves overlapping two pieces of metal, with the weld applied along the intersection. It is ideal for connecting components with different thicknesses, providing a reliable bond for many sheet metal and repair applications. Pipes through bulkheads In the case of a corrugated bulkhead, it becomes necessary to fit filling pieces between the troughs in way of the shelf plate. If possible, the passage of piping and ventilation trunks through watertight bulkheads is avoided. However, in several cases this is impossible and to maintain the integrity of the bulkhead the pipe is flanged at the bulkhead. Where a ventilation trunk passes through, a watertight shutter is provided. Pipes through bulkheads Testing Watertight Bulkheads Both the collision bulkhead, as the fore peak bulkhead, and the aft peak bulkhead provided they do not form the boundaries of tanks are to be tested by filling the peaks with water to the level of the load waterline. All bulkheads, unless they form the boundaries of a tank which is regularly subject to a head of liquid, are hose tested. Since it is not considered prudent to test ordinary watertight bulkheads by filling a cargo hold, the hose test is considered satisfactory. The end