12 erection of bulk units

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12 ERECTION OF BULK UNITS

12.1 AIMS OF THE LECTURE

a) To outline the procedures of lifting the blocks,units and modules to the building berth or

dock.

b) To explore the erection scheduling methods.

c) To examine the hazards in lifting bulk structure

12.2 LIFTINGPROCEDURES

Lifting procedure is a method of lifting the ships bulk structure such as blocks, units, and

modules to the building berth or dock. The procedure should be well considered because it

involves large and heavy structures, which conceives many hazards both to the production

process as well as to the human safety.

The lifting procedure considerations would include the followings:

a)

Lifting facilities

The lifting facilities available for lifting the blocks onto the berth or dock should be identifiedfar before the blocks are ready to be lifted. It was when the size and weight of the blocks

were determined prior to their construction in the assembly shop.

Cranes that are commonly used for lifting the blocks are gantry crane which is also known as

Goliath crane, telescopic mobile crane, hammerhead crane, floating crane, and level luffing

crane.

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The decision of using the type and capacity of certain crane is based on investment cost and

utilisation of the crane, the type and size of ships will be built, the efficiency and practicality

of using it etc., some considerations of choosing the type of crane are shown in the following

matrix of merits and drawbacks:

No Type of crane Merits Drawbacks

1 Goliath crane -High lifting capacity

-Can cover the whole area of

dock or berth

-Very stable

-

Good operator visibility

-High invesment cost

-Not applicable on side

launch berth

2 Telescopic mobile

crane

-Can move around easily

-Suitable for lifting small

units

-Lower investment cost

-Can be hired

-Limited in lifting capacity

-Not very stable

-Limited operator visibility

-Limited coverage

3 Hammerhead crane -High lifting capacity

-Very stable

-Good operator visibility

-Good coverage

-Applicable for side launch


-Operate only from one side

4 Floating crane -High lifting capacity

-Can be operate from water

front

-Good for complementary

task

-Limited coverage

-Limited stability


-Not applicable on end

launch

-Limited operator visibility

-

5 Level luffing crane -High lifting capacity

-Can work in tandem

-

Applicable in all type oflaunch

-Limited stability

-Limited coverage

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b)Size and weight of blocks

In most modern shipyards that implement advanced outfitting method blocks and modules are

completed in the assembly shop or on the assembly yard, in order to minimise the joining

process on the berth or dock. It is a common practice to construct the blocks as large as

possible as the lifting facilities allow.

There are some advantages in having large and complete blocks to be erected to the berth or

dock, but the drawbacks should also be considered.

Advantages and disadvantages of large block structure

Advantages Disadvantages

Minimum work on berth/dock Need high capacity of cranage

Shorter construction time on berth/dock Demand high accuracy of block structure

Better product quality More difficult to align the blocks

Less disruption to complete the block Need higher skill to lift the blocks

Some considerations that should be made in deciding the size and weight of the blocks with

regard to the efficientcy, practicallities, and cost effectiveness of the shipyard are as follows:

The capacity of the transporter available to transfer the blocks to the berth or dock.

The lifting capacity of cranes available on the berth or dock.

The access available for transporting the blocks to the berth or dock.

The alignment methods that will be implemented on berth or dock.

The lifting methods that will be implemented.

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d)Preparation of reference lines and points

For proper alignment of the blocks on building berth or dock reference lines are drawn on the

floor and walls (for dock) with some indication of their positions relative to the centerline for

floor reference lines, and relative height and distances from the floor for horizontal and

vertical reference lines as shown in the following illustration:

Reference lines and reference points are not only drawn on the floor and walls of the berth or

dock, but also drawn on the blocks and on some of their structural members.

Prior to joining the block is positioned on the prepared stools or on top of other blocks, the

reference lines and reference points are used as guidance for its correct position.

e)block alignment

Unlike building a boat or conventional method where the ship was constructed piece by

piece, most of the ships now are built in blocks and modules. The blocks and modules are

aligned on their designated positions prior being tack welded and joined one to another.

Block alignment is important for obtaining a good shape of the ships hull, and for proper

joining of the internal structural and outfiting parts.

In block aligning reference lines and points both on the berth and on other blocks are used as

guidnace for its position, and a number of tools are also being used such as theodolite and

laser beam.

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12.3 ERECTION SCHEDULE

The completion of blocks joining dependent on the launching method that will be

implemented. If the ship is launched on the slipway for safety reasons, most of the super

structure usually will be completed on the quay after the launching, but if the ship is floated

out the whole structure would be completed on the berth or dock.

The effectiveness of blocks joining process among other things will be determined by the

block erection schedule. Many aspects should be considered in order to obtain an optimum

block erection schedule these include:

The position of blocks in the ship structure

The blocks joining sequences

The work content and the time needed to construct each block in the shop

The work content and the time needed to join each block

Traditionally block erection schedule was done manually using past project or experienced

data, which generally very time consuming and very unaccurate. Some computer

programmes have been introduced to do the scheduling task using numerical algorithm and

visual simulation.Information for block erection schedule would come in many ways include:

Network diagram

Blocks layout sketches

Block erection matrix

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BlockNumber

PrecediBlock

DB 3 PS DB 4 S

DB 3 SB DB 3 P

DB 2 PS DB 3 S

DB 2 SB DB 2 P

DB 1 PS DB 2 S

DB 1 SB DB 1 P

.

g SuccessingBlocks

Erection Due Joini(

B DB 3 SB 3 Jan 09

S DB 2 PS 6Jan 09

B DB 2 SB 9 Jan 09

S DB 1 PS 12 Jan 09

B DB 1 SB 15 Jan 09

S FP 1 19 Jan 09

.

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ng timeays)

3

3

3

3

4

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12.4 LIFTING HAZARDS

There are some hazards that need to be anticipated in lifting a bulk structure such as block,

module, and unit, because of the potential risks that might create fatal consequences both to

the human safety as well as to the work being carried out.

a)

Identified hazards

The lifting hazards that may be identified among other things are:

Unsymmetrical shape of the module, unit, or block being lifted that might causeunballance lifting and the structure fall down.

Size and weight of the structure being lifted that make the lifting process more dificult

to control.

Cranes working in tandem might cause unsynchronised movement and lifting speed

and break the ropes or lifting points.

Improper securing of lifting points which might caused the lifting points pulled off thestructure.

Inaccurate positioning of the structure which can cause mismatch of the joining parts.

Unqualified operator being emplyed may violate the lifting procedures

b)Potential risks

The potential risks due to lifting hazards can be categorised into two groups as follows:

Production risks Safety risks

Rework Injury to the people

Damage of the structure Inconvenient working conditionLengthen the production time Work disruption

Extra working cost

Work does not meet the standards

c)Risks reduction

Actions that could be made to reduce the risks due to lifting hazards are:

Implement proper lifting procedures

Employ qualified lifting operators

Examine the structure and the facilities before undertaking the task

Arrange the lifting points properly by considering the shape and weight of the

structure

12.6 CONCLUDING REMARKS

a) Lifting procedure is a method of lifting the ships bulk structure to the building berth or

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b) The lifting procedure considerations would include:

Lifting facilities

Size and weight of blocks

Arrangement of lifting points

Preparation of fererence lines and ponits

Blocks alignment

c)Considerations on erection schedule should include:

The position of blocks in the ship structure

The blocks joining sequences

The work content and the time needed to construct each block in the shop

The work content and the time needed to join each block

d)

Hazards that need to be identified in lifting bulk structure include:

Unsymmetrical shape of the structure

Size and weight of the structure

Cranes working in tandem

Improper securing of lifting points

Inaccurate positioning of the structure

Unqualified operator being employed

e)Potential risks in lifting bulk structure can be grouped into production risks and safety

risks.

f) Some consideration for reducing risks include:

Implement proper lifting procedures

Employ qualified lifting operators

Examine the structure and the facilities before undertaking the task

Arrange the lifting points properly by considering the shape and weight of the

structure

12 erection of bulk units

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