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Risk of ships structure damage during cargo operation and how to prevent
Damage prevention check items on board bulk carriers
: The traditional design and configuration of single-side skin bulk carriers presents obstacles to safe and efficient cargo handling, especially discharge with grabs. The usual types of damage that occur during grab discharge operations are grab and payloader damage in the holds, damage to hatch coamings and covers, and damage to deck fittings and equipment.
Grab damage in the holds can be classified into three categories:
1. Damage to ladders or coamings during free digging.
2. Damage to frames and hopper side during the second phase of digging.
3. Damage to the tank top during the third phase of digging.
Deck crane mounted with grab
Prevention of damage to ladders
When free digging the Operator should: Check for the location of sloping ladders with intermediate platforms extending into the hold space, check if it is going to the outboard or inboard side, and check for the location of platforms.
Check location of vertical ladders and look out for intermediate platforms.
Work carefully across each end of the hold in turn, keeping clear of the ladders until the cargo falls away and the handrails and intermediate platforms can be seen.
i) Ladder may be buried under the cargo with only the top section visible. ii) Grab may topple over and strike the ladder, so make due allowances.
Fig: bulk terminal grab-operation
Prevention of damage to hoppers and sides frames by grab
a) Grab evenly over the full area of the hold to avoid development of steep banks in the wings.
b) Avoid pendulum swinging of the grab into the wings so that it will not strike the ship's side shell frames.
c) Grab should be straight and parallel to the ship's side.
d) Do not land the grab on the hopper side where bare steel is visible.
e) Do not attempt to land the grab close to the foreward and after bulkheads, as there may be an outward sloping stool plate under the cargo.
f) Operate grab from the highest point of the cargo at all times.
g) Any damage to the frames may affect the seaworthiness of the ship, and has to be reported to the master.
h) Avoid swinging the grab in at an angle, as the corner of the grab may strike the hopper tank first. This will cause heavy indents or puncture holes in the tank plate.
Prevention of damage to inner bottom plating (tanktop)
Lower the grab carefully and evenly on to the tank top. Never drop the grab at speed. Be particularly careful where there are mounds of cargo on the tank top. One side of the grab will land safely on the cargo but the other side may drop corner first on to bare steel. If it lands heavily it can puncture the tank top.
Prevention of damage to hatch coamings and covers
The operator should always check along the line of hatches that the covers are completely opened clear of the coaming. The travel of the grab into the hold should be controlled so that the grab and the grab trolley are in line as the grab is moving out and down into the hold. This will ensure that the swing is under control at all times.
When working in the wings the grab trolley should be positioned so that the grab ropes and the grab itself are raised clear of the coaming.
This is caused by grab or rope contact with the coamings or covers. Ship's crew may:
Leave covers slightly closed over the top of the coaming to prevent spillage getting into the drain channels.
Fail to secure the open covers in place, which can allow them to roll closed.
Always be aware that the ship can move in or out, fore and aft, and up and down due to wind, tide, movement of cargo and ballast, or crew adjusting mooring ropes.
Raising or lowering the grab close to the coaming may result in the grab or the grab rope shackles catching on the lips of the hatch cover. This will result in the cover being lifted and dropped heavily, causing major damage to the coaming, the cover and the cover drive mechanism.
Damage to the cross-joint sealing arrangement could also occur.
Prevention of damage by payloader to bottoms of ladders, stool plates and bulkheads
In co-ordination with the master, the operator should be informed of:
Location of the bottoms of ladders.
Location of any pipes or pipe guards.
Location of bilge covers plates.
Payloader drivers should:
Operate carefully around ladders and projections. Remove material manually where necessary.
Avoid grinding the corners of the payloader bucket along the bottom of the bulkheads and hopper tanks, as this kind of heavy pressure can cause unseen damage.
The master should point out the position of any obstructions on the tank top. On some ships the locations of bilge cover plates are marked by a line of paint on the bulkhead.
Prevention of damage to deck fittings and equipment
Before travelling the unloader to a new location.
Check that the grab is well clear of all deck fittings and equipment before moving.
Check that it is clear for the unloader to long travel.
When working close to the bridge front or foremast make due allowances for aerials and other obstructions to the unloader boom and keep well clear.
Derrick and crane jibs not in use should be lowered below the level of the unloader boom.
As the ship rises up as the cargo is unloaded, the unloader operator should always check that there is safe clearance over all obstructions before attempting to move the unloader. The unloader boom should always be raised before moving if there is any doubt.
Error inducing conditions
The following conditions may lead to operator error or misjudgement:
Overfilled or unevenly filled holds having ladders and platforms buried under the cargo.
Environmental conditions poor lighting, dust, glare, fog.
Mechanical or control problems on the unloader faulty grab controls, slipping winch brakes, slipping long travel brakes.
Poor working conditions such as poor conditions in the operator cab, faulty indicators, inadequate means of communications with ship and/or co-workers, faulty seat, dirty windows.
Never grab from the foreward and aft ends of the holds without being sure of where the ladders are.
Do not work unless the cargo in the hold is clearly visible.
All equipment faults should be reported to the terminal representative or relevant maintenance person immediately.
Unloader operation is a demanding job that requires concentration and care. Deficiencies and problems that distract the operator should be rectified immediately.
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- Bulk carrier hull damage - causes and preventive measures
- How to avoid damage during cargo operation
- How to arrange repair of damage during cargo loading/unloading
- Causes of bulk carrier hull damage and failure in operation
- Bulk carrier water ingress problem
- Encountering hazards in bulk carriers - Possible sources
- Preparation for ships carrying bulk cargo & standard loading condition
- Design of ships longitudinal subdivisions & of transverse watertight bulkheads
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- Definitions of available Bulk carrier sizes
- Tank construction & required strength for ships carrying bulk cargo
- Handling water ingress problems in bulk carrier, investigation and countermeasures
- Survival and safety procedure for bulk carriers
- Hatch cover strength requirement for a seagoing bulk carrier
Our detail pages illustrated many safety aspects of Bulk carrier
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Operation of sea going bulk carriers involved numerous hazards . Careful planning and exercising due caution for all critical shipboard matters are important . This site is a quick reference to international shipping community with guidance and information on the loading and discharging of modern bulk carriers so as to remain within the limitations as specified by the classification society.
It is vital to reduce the likelihood of over-stressing the ship's structure and also complying with all essential safety measures for a safe passage at sea. Our detail pages contain various bulk carrier related topics that might be useful for people working on board and those who working ashore in the terminal. For any remarks please Contact us
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