Wednesday, 20 June 2012

Bulkheads

Bulkheads
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There are three basic types of bulkhead, watertight, non watertight and tank.
Different types of bulkheads are designed to carry out different functions.

    The watertight bulkhead several important ones;
    1. It divides the ship into watertight compartments giving a buoyancy reserve in the event of hull being breached. The number of compartments is governed by regulation and type of vessel
    2. cargo separation
    3. They restrict the passage of flame
    4. Increased transverse strength, in effect they act like ends of a box
    5. Longitudinal deck girders and deck longitudinal are supported by transverse watertight bulkheads which act as pillars

Number of bulkheads (cargo ship)


Length of ship (m)Number of bulkheads
AboveNot exceedingMachinery midshipsMachinery Aft
9010555
10511565
11512566
12514576
14516587
16519098
190To be considered individuallyTo be considered individuallyTo be considered individually
The number of bulkheads depends upon the lenght of the ship and the postion of the machinery. There must be a collision bulkhead positioned at least 1/20th of the distance from the forward perpendicular. This must be continuous 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 continuous deck above the waterline. The engineroom must be contained between two watertight bulkheads one of which may be the after peak bulkhead.
Each main hold watertight bulkhead must extend to the uppermost continuous deck unless the freeboard is measured from the second deck in which case the bulkhead can extend to the second deck.
A water tight bulkhead is formed from plates attached to the shell, deck and tank top by means of welding. The bulkheads are designed to withstand a full head water pressure and because of this the thickness of the plating at the bottom of the bulkhead may be greater than that at the top. Vertical stiffeners are positioned 760mm apart except were corrugated bulkheads are used.

Watertight bulkheads must be tested with a hose at a pressure of 200 Kn/m2 . The test being carried out from the side on which the stiffeners are fitted and the bulkhead must remain watertight.
Water tight bulkheads which are penetrated by pipes, cables etc. must be provided with suitable glands which prevent the passage of water.

Water tight doors


Vertically mounted watertight door

watertight doors To allow the passage for personnel water tight doors are fitted , openings must be cut only were essential and they should be as small as possible. 1.4m high, 0.7m wide being the usual. Doors should be of mild steel or cast steel, and they may be arranged to close vertically or horizontally.
The closing action must be positive i.e. it must not rely on gravity. Hinged water tight doors may be allowed in passenger ships and in watertight bulkheads above decks which are placed 2.2m or more above the waterline. Similar doors may be fitted in weather decks openings in cargo ships.

Hinged water tight door

Dogs mounted on watertight door Hinged water tight doors consist of a heavy section door which when closed seals on a resilient packing mounted in channel bar welded to the door frame. The door is held firmly in the door frame when closed by the dogging arrangements shown which allow the doors to be opened from either side.Normally six of these dogs are spread equally around the periphery.

Automatic watertight operating gear

automatic watertight operating gear Automatic operating gear allows the remote operation of watertight doors. These are fitted on many vessels including passenger ships.
In the event of fire or flooding, operation of switches from bridge/fire control area sends a signal to an oil diverter valve. Oil from a pressurised hydraulic system is sent to a ram moving the door.
The door may also be operated locally by a manual diverter valve. In addition, in the event of loss of system pressure the door may be operated by a local manual hand pump
remote door position indicators are fitted as well as were appropriate alarms to indicate operation.

Bulkhead definitions

Class A Are divisions forming bulkheads and decks that;
    • Constructed of steel or equivalent
    • suitably stiffened
    • Prevent passage of smoke and flame to the end of one hour standard fire test
    • Insulated using non-combustible material so that average temperature on exposed side does not rise above 140oC and point temperature above 180oC. The time the bulkhead complies with this governs its class
      A-60 60min
      A-30 30Min
      A-15 15Min
      A-0 0Min
Class B
These are divisions formed by bulkheads, decks, ceilings and lining
    • Prevent passage of flame for first half hour of standard fire test
    • Insulated so average exposed side temperature does not rise more than 139oC above original and no single point rises more than 225oC above originalThe time the bulkhead complies with this governs its class
      B-15 15Min
      B-0 0Min
    • Constructed of non-combustible material and all materials entering the construction are similarly non-combustible except where permitted
Class C
These are divisions constructed of approved non-combustible materials. Combustible veneers are allowed were they meet other criteria

Main vertical zones Divided by Class A bulkheads and not exceeding 40m in length

1 comment:

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