ship construction- bulkhead
TRANSCRIPT
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
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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
Maritime Lecturer & Trainer, Bangladesh.
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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Mohd. Hanif Dewan, Chief Engineer and
Maritime Lecturer & Trainer, Bangladesh.
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
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Maritime Lecturer & Trainer, Bangladesh.
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
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Maritime Lecturer & Trainer, Bangladesh.
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
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Maritime Lecturer & Trainer, Bangladesh.
Plain Bulkhead
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Maritime Lecturer & Trainer, Bangladesh.
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
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Bulkheads, attachments
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Maritime Lecturer & Trainer, Bangladesh.
Corrugated Bulkheads
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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
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Maritime Lecturer & Trainer, Bangladesh.
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
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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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Maritime Lecturer & Trainer, Bangladesh. 19
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Maritime Lecturer & Trainer, Bangladesh. 20
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
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Maritime Lecturer & Trainer, Bangladesh. 21
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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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Maritime Lecturer & Trainer, Bangladesh. 29
WATERTIGHT DOORS
Class 2 Watertight Door
• 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
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WATERTIGHT DOORS
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WATERTIGHT DOORS
WATERTIGHT DOORS
Class 3 Watertight Door
• 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.
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Class 3 Watertight Door
• 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
Class 3 Watertight Door
• 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
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Maritime Lecturer & Trainer, Bangladesh. 34
WATERTIGHT DOORS
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Maritime Lecturer & Trainer, Bangladesh. 35
WATERTIGHT DOORS
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Maritime Lecturer & Trainer, Bangladesh. 36
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)
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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
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Maritime Lecturer & Trainer, Bangladesh.
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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Mohd. Hanif Dewan, Chief Engineer and
Maritime Lecturer & Trainer, Bangladesh.
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.
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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
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Maritime Lecturer & Trainer, Bangladesh. 44