Fig :Handling heavy weight
The calculations are based on the ship being upright in calm conditions (i.e. in port) and take account of the static weight of the stack due to gravity.
The figures also take into consideration the anticipated dynamic stack loads acting on the deck or hatch covers in adverse weather due to the various ship motions described earlier.
However, stack weight limits do not ensure that the dynamic loads acting on the container securing system will remain within the margins of safety during heavy weather.
Loading the cargo so that each stack does not exceed its total permissible weight is relatively easy to achieve. It is far more difficult to optimize the stack in terms of weight distribution, port rotation and estimated forces, ensuring that at all times the safe working load of the securing equipment is not surpassed.
Therefore it is vital that the Cargo/Container Securing Manual is consulted for guidance.
The manual gives illustrations of typical safe stack weight distributions and total safe stack weights based on the design limits of the shipís securing system.
Metacentric height (GM)
The higher the GM, the greater is the righting moment when the ship is rolling.
Consequently, the transverse acceleration forces acting on a container deck cargo and the securing system intensify with any rise in GM. Such forces are at their highest at the extremity of each roll.
It is always important to consider the effect of GM on the securing system when estimating the forces, bearing in mind that GM may not remain constant throughout the voyage.
Estimating the forces
Examples of GM values are featured in the Cargo/Container Securing Manual together with acceptable weight distributions in each case. This information should be compared with the actual figures as calculated by the ship. If there are any significant differences, stack weights and/or securing equipment should be adjusted until both are deemed to be within prescribed safe limits.
For reliability and accuracy, many vessels are now equipped with a container securing software package. There are several programs of this type on the market, most of which are designed to interface with cargo management or loading computer software.
Securing programs will calculate the applicable forces for any given stowage plan, comparing the data with the safe working criteria as specified by class. The effect of wind strength on the outboard stacks is also taken into account, allowing the corresponding load on the securing system to be adjusted accordingly.
Most programs will warn if any securing components or individual container frames are likely to be overloaded, and the result of applying additional lashings can be shown.
Inspection, Inventory and Maintenance
The type of securing equipment used on board depends on the shipís design, capacity and trade. Accurate records regarding the quantity, location, inspection, maintenance, repair and replacement of such equipment should always be kept.
In general terms there will be a need to:
Ensure that the amount of securing equipment and lashing material retained on board is sufficient to properly secure the maximum number of containers to be carried. There should also be an adequate safe margin of spares and replacements.
Inspect all portable securing equipment (e.g. turnbuckles, lashing rods, twistlocks, twist stackers etc) for signs of distortion, buckling, corrosion, cracking and/or excessive wear. As far as practicable, such checks should be carried out as a matter of routine before the equipment is reused.
Lubricate turnbuckles and twistlocks frequently. The spring which holds the twistlock in the closed position should be examined regularly as it may become less effective over time, causing the device to unlock if the ship or stow begins to flex on passage.
Examine all fixed fittings (e.g. container sockets, elephantís feet, dovetail connections) routinely for signs of wastage, cracks, distortion and/or general deterioration, including base plates where applicable. Particular care should be paid to the condition of D rings, mindful that wastage of the main shaft may be concealed by the retaining sleeve.
Maintain a file of all certificates of approval relating to the portable securing equipment carried on board.
Suspect fittings or equipment should always be removed from service when found, and repaired or replaced as necessary.
Containership operation : Cargo Securing
Containership operation : Common reasons for stowfall
Basic guideline for Container Ship Operation
Containership operation: Cargo hold ventilation Containership operation: Safety of personnel Containership operation: wet damage in cargo hold
Reefer cargo Handling In PortReefer cargo care at seaCommodities Shipped In Reefer ContainersReefer Cargo Temperature RecordingReefer Cargo Maintaining RecordsReefer Cargo DefrostingBasic check item prior stowing Reefer Cargo Preventing Reefer Cargo deterioration
Container handling additional guideline:
Containership cargo stowage and planning
Stacking Weights Restrictions Lashing strength calculation Dangerous goods stowage and segregation Reefer Container Stowage
Out of Gauge Container Stowage
Special Container Stowage
20 or 40 or 45 feet Compulsory Stowage Locations
Irregular Stowage of Containers
Over-stow of Containers
Hatch Cover Clearance (High cube containers Under Deck )
Other matters regarding cargo stowage as necessary
How to load maximum number 20 feet container on deck ?
What are the extra precaution should be taken prior loading a 45 feet container on deck ?
Container damage in ''2 in 1'' cargo Operation
Modern containership & loading of various container types
How to load containers coming in different forms/sizes
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How to prevent injury onboard
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Reefer cargo handling
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DG cargo handling
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