Ship Construction- Bulkhead

Mohd. Hanif Dewan, Chief Engineer and Maritime Lecturer & Trainer, Bangladesh.

SHIP CONSTRUCTION-

BULKHEAD

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 transverse and longitudinal bulkheads dividing the ship into a number of compartments. There are others, which are of little structural importance, but they act as screens further dividing compartments into small units of accommodation and stores.

The three basic types of bulkheads found on most ships, are: i. watertight, ii. non-watertight and iii. oiltight or tank bulkheads. i. Watertight: The main transverse watertight bulkheads divide the ship into a number of watertight compartments and their number is dictated by classification society regulations. ii. Non-watertight: Non-watertight bulkheads are any other bulkheads such as engine casing, accommodation partitions or stores compartments.

iii. Oiltight bulkhead: Oiltight bulkheads form boundaries of tanks used for the carriage of liquid cargoes or fuels.

BULKHEADS

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Maritime Lecturer & Trainer, Bangladesh.

BULKHEADS

Functions of bulkheads • subdivision • contain flooding in the event of damage, • transverse strength member • protection against racking stresses • effective barrier against the spread of fire. • resisting any tendency for transverse deformation of the ship

BULKHEADS

• Transverse Watertight Bulkheads

- subdivide a ship against flooding and spread of fire

- support decks

- resist racking stresses

- maintain transverse form

- number and spacing of WT bulkheads governed by

statutory requirements

• Longitudinal Watertight Bulkheads

- provide longitudinal strength

- control width of flooding & prevent excessive list

- subdivide liquid cargoes & reduce free surface effect

- prevent spread of fire



BULKHEADS

• Transverse W/T Bulkheads – Requirements in Cargo

Ships

• Governed by statutory regulations for subdivision, floodability and damage stability with minimum 3 (for ships with machinery aft) or minimum 4 (for ships with machinery amidships), including:

• A Collision Bulkhead watertight to freeboard deck,

spaced between 5% (or 10m whichever is less) and not

more than 8% of ships length from FP – allowance made

in case of extensions like bulbous bow forward of FP

• An Aft Peak Bulkhead enclosing the stern tube and

rudder trunk in a W/T compartment - may extend to

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Mohd. Hanif Dewan, Chief Engineer and


BULKHEADS

• Transverse W/T Bulkheads – Requirements in Cargo Ships

• A Bulkhead at each end of the machinery space

watertight upto the freeboard deck (one of these could be the aft peak bulkhead on ships with machinery space aft)

• Additional bulkheads are fitted as required by class rules, depending on ships length at uniform intervals.

• Any changes in intervals will need suitable transverse stiffening

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BULKHEADS • Transverse W/T Bulkheads – Requirements in Passenger

Ships

• Governed strictly by statutory regulations for subdivision,

floodability and damage stability with minimum 3 (for ships

with machinery aft) or minimum 4 (for ships with machinery

amidships), including:

• A Collision Bulkhead watertight to the bulkhead deck,

spaced not less than 5% and not more than 3m + 5% of

ships length from FP – allowance made in case of

extensions like bulbous bow forward of FP

• An Aft Peak Bulkhead watertight to the bulkhead deck

but may be stepped below bulkhead deck if subdivision

safety is not compromised



BULKHEADS

• Transverse W/T Bulkheads – Requirements in

Passenger Ships

• A Bulkhead at each end of the machinery space

watertight upto the bulkhead deck

• stern tube to be enclosed in a W/T compartment

• stern gland to be situated in a W/T shaft tunnel, or space

separate from the stern tube compartment, of specifically

calculated size



BULKHEADS

Construction of plain watertight bulkheads

Watertight bulkheads because of their large area are formed of several strakes of plating. They are welded to the shell, deck and tank top. The plating strakes are

horizontal and the stiffening is vertical. Since water pressure in a tank increases

with depth and the watertight bulkhead must withstand such loading, the

bulkhead must have increasingly greater strength towards the base. This is

achieved by increasing the horizontal strakes of plating towards the bottom.

The collision bulkhead must have plating some 12% thicker than other watertight

bulkheads. Also, plating in the aft peak bulkhead around the sterntube must be

doubled or increased in thickness to reduce vibration. The bulkhead is stiffened

by vertical bulb plates or toe-welded angle bar stiffeners spaced about 610mm for

collision and oiltight bulkheads.

The ends of stiffeners are bracketed to the tanktop and the deck beams. In tween

decks, where loading is less, the stiffeners may have no end connections.

Plain Bulkhead



BULKHEADS

Corrugated watertight bulkheads (construction)

The use of corrugations or swedges in a plate instead of welded stiffeners produces as strong a structure with a reduction in weight. The troughs are vertical on transverse bulkheads but on longitudinal bulkheads they must be horizontal in order to add to the longitudinal strength of the ship.

The corrugations or swedges are made in plating strakes prior to fabrication of the complete bulkhead. As a consequence, the strakes run vertically and the plating must be of uniform thickness and adequate to support greater loads at the bottom of the bulkhead. This greater thickness

of plate offsets to some effect the saving in weight through not adding stiffeners to the bulkhead. The edges of the corrugated bulkhead which join to the shell plating may have stiffened flat plate fitted to increase transverse strength and simplify fitting the bulkhead to the shell. On high

bulkheads with vertical corrugations, diaphragm plates are fitted across the troughs. This prevents any collapse of the corrugations.

Corrugated bulkhead



Bulkheads, attachments



Corrugated Bulkheads

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Maritime Lecturer & Trainer, Bangladesh. 16

Cofferdam bulkheads

These bulkheads extend from the keel to deck

across the full breadth of the ship.

A "cofferdam" is an isolating compartment

between two adjacent steel bulkheads.

Strengthening of this bulkhead is normally on

one side (i.e.) in the cofferdam, with the side

facing the hold being flush.

BULKHEADS



BULKHEADS

• The strength of a bulkhead is tested by filling up the tank with water up to the bulkhead deck

• Access is provided through the bulkheads by watertight doors

• All openings of bulkhead are to be made watertight in order to maintain the watertightness of the bulkheads

• Watertightness of bulkhead opening is determined by the types of watertight doors used



BULKHEADS

• The strength of a bulkhead is maintained in way

of opening by the following method:

a. insert plate around the opening

b. face bar to be fitted on the opening for Class 1

watertight door and brass facing strip for Class 2

& 3. The corners of the opening are radiused

c. web frames fitted beside the class 1

watertight door opening to strengthen the

bulkhead

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BULKHEADS

BULKHEADS

Penetration of bulkhead by electrical cables

• The electrical cables passed through a conduit or

pipes that are threaded near the bulkhead

• A gland and packing arrangement is used to

prevent the leakage of liquid along the conduit

• A gasket is placed on the bulkhead and tightened

up with a nut that run on the threaded gland on top

to ensure watertightness on the bulkhead opening





BULKHEADS

WATERTIGHT DOORS

Watertight doors in bulkheads

Watertight doors are sometimes required to be fitted on bulkheads,

examples of such doors include the one being fitted so that a direct

access is provided between the engine room and the shaft tunnel. The

number of doors on a ship must be an absolute minimum as possible

compatible with the safe working of the ship.

Door operation

Doors to have two sources of power. Hydraulic fluids to be non-

freezing. Door control to be operable from both sides of the door and

power control within reach of the doorway.

WATERTIGHT DOORS

Speed of operation

All power operated doors must be capable of being closed

from the remote position within one minute. When being

closed it must be accompanied by an audible alarm.

Doors must be closed promptly in an emergency to prevent

progressive flooding – potentially very hazardous,

especially Ro-Ro ships.

Doors should close at a uniform rate in not less than 20

secs, but not more than 40 secs when the ship is upright.

WATERTIGHT DOORS

Watertight doors inspections and instructions

• W.T. doors and control gear must be inspected at least once in seven days.

• All doors in normal use must be opened and closed daily. • All crew members should be instructed on the safe operation of W.T. doors.

• Written instructions must be available.

Watertight doors doors types

Type A – a door which may be left open.

Type B – a door which should be closed it may remain open only whilst personnel are working in the adjacent compartment

Type C – a door which should be closed. It may be opened for sufficient time to permit through passage.

All doors must be closed in a potentially hazardous situation except for the passage of personnel.

Watertight doors – classification

There are 3 classes of watertight doors, which are

as follows:

- Class 1, Hinged doors

- Class 2, Hand operated Sliding Doors

- Class 3, Power operated, (hand operated) sliding

doors

WATERTIGHT DOORS

Class 1 Watertight Door

• It is categorized as Hinged/Weathertight Door

• It shall be fitted with quick action closing devices,

such as catches, workable from each side of the

bulkhead.

• It is fitted into structures above the freeboard deck

• The doors are steel suitably stiffened, with a rubber

gasket fitted to effect watertightness.

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WATERTIGHT DOORS


• Hand operated sliding doors that may have a

vertical or horizontal motion.

• It is possible to operate the mechanism at the door

itself from either side, and above the bulkhead

deck.

• When operating a hand gear, the time necessary

for the complete closure of the door with the

vessel upright, shall not exceed 90 seconds



WATERTIGHT DOORS



WATERTIGHT DOORS

WATERTIGHT DOORS


• Power operated sliding door which may have a

vertical or horizontal motion.

• If it is being operated from a central control, the door

must also be operated by power at the door itself

from both sides.

• The door will close automatically if opened by local

control after being closed from the central control.




• It is provided with hand gear workable at the

door itself on either side and on bulkhead deck.

• Warnings by sound signal that the door has

begun to close and will continue to move until it

is completely closed.

• The door shall take a sufficient time to close to

ensure safety.

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WATERTIGHT DOORS


• There shall be at least two independent power sources capable of opening and

closing all the doors under control

• A de-wedging device may be fitted to release the door from the wedge frame and

to avoid overloading the power unit if the door meets an obstruction



WATERTIGHT DOORS



WATERTIGHT DOORS

Testing of watertight door

• Each watertight door is tested by water pressure to a head of water up to the

bulkhead deck (either before or after the door is fitted)



WATERTIGHT DOORS

BULKHEADS

• Some important definitions:

– Margin line

• an imaginary line drawn parallel to and at least 76mm below the

upper surface of the bulkhead deck at side a ship is deemed to

remain afloat after flooding if calculations show that the margin line is

not submerged used for passenger ship subdivision criteria

– Bulkhead deck

• Uppermost deck to which transverse W/T bulkheads are carried

• Normally the freeboard deck

– Weather deck

• Uppermost continuous deck exposed to weather and sea

• Openings on the weather deck are weathertight and below it are

watertight



BULKHEADS

• Some important definitions: – Weathertight

• means that in any sea condition water will

not penetrate into the ship

– Cofferdam

• an isolating compartment formed between

two adjacent W/T or oiltight bulkheads

• strengthening is usually on the side inside

the compartment

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BULKHEADS

• Testing of Watertight Bulkheads/Tanks

Bulkheads

– hose tested, unless they form boundary of a tank subjected to

head of liquid

Collision Bulkheads and Aft Peak Bulkheads

– If not used as tanks, tested by filling with water upto the load waterline or maximum head in case of damage

– If used as tanks, tested by subjecting to water head to which they might be in service (ie top of airpipe)

Deep tanks

– They are tested by subjecting them to a maximum head of water to which they might be in service (i.e. to the top of the airpipe). This should not be less than 2.5m above the crown of the tank.



BULKHEADS

Testing of Watertight Bulkheads/Tanks

Double Bottom Tanks:

They are tested on completion with a head of water representing the maximum pressure head which may be experienced in service, i.e. to the top of the air pipe. Alternatively air testing is carried out before any protective coatings are applied. The air pressure may be raised to 0.21 kg/cm2, and then lowered to a test pressure of 0.14 kg/cm2. Any suspect joints are then subjected to a soapy liquid solution test. Water head structural tests will be carried out on tanks selected by the surveyor in conjunction with air tests carried out on the majority of tanks.

WATERTIGHT FLOOR

A watertight floor is fitted directly below every main transverse bulkhead.

Regulations regarding openings in a watertight bulkhead

1. Where frames or beams pass through a bulkhead, such a bulkhead shall be made structurally watertight without the use of wood or cement

2. Pipes piercing the collision bulkhead shall be fitted with suitable valves operable from above the freeboard deck and the valve chest shall be secured at the bulkhead inside the forepeak. The valves may be fitted on the after side of the collision bulkhead provided that the valves are readily accessible under all service conditions and the space in which they are located is not a cargo space. All valves shall be of steel, bronze or other ductile material. Valves of ordinary cast iron or similar material are not acceptable. Two pipes may be allowed to pierce the collision bulkhead if

the forepeak is divided into two compartments. These compartments must be designed to hold two different liquids.

WATERTIGHT FLOOR

3. No door, manhole, ventilation duct or other opening shall be

fitted on the collision bulkhead.

4. Pipes passing through bulkheads are either welded, or

fastened to the bulkhead by studs or bolts screwed through

tapped holes in the plating. They must not be secured by ordinary

bolts passing through clear holes in the plating. This ensures that,

if the bolt breaks, part of it will be left in the bulkhead; otherwise a

clear hole might be left in the plating.

5. Where a ventilation trunk passes through, a watertight shutter

is provided.

ANY QUESTION?

THANK YOU! 8/23/2014



Ship Construction- Bulkhead

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Transcript of Ship Construction- Bulkhead