Tanker Notes ||
Container Ship Operations ||
Ocean Navigation ||
Severe Wind and Rolling affecting hull strength & stability of Container ship
Purpose of IMO severe wind and rolling criterion is to evaluate the vesselís ability to survive severe beam seas and wind. Such a situation may be assumed to occur should the vessel lose steering or propulsive capability in a storm, in which case it will likely end up wallowing in beam seas.
If the vessel can roll freely back to leeward under the combination of all of these forces (assumed wind, beam seas and vessels momentum gathered in a roll) without rolling past its range of positive stability (capsize point), or taking on water though open down flooding points (such as the Engine room air inlets), it passes the requirement.
Most cargo stowage and stability calculation software provide Alarms / Highlights for stability conditions not complying with IMO severe wind and rolling criterion. Compliance must be confirmed.
Forces on containers during transportation
Cargo transportation often involves different modes of transport,
by road, rail and/or sea. Often, combined cargo transport units like
containers will set out by road, continue by sea and perhaps conclude
as rail freight. Cargo transported by combined means must
be stowed and secured so as to withstand the forces involved in all
the modes of transport used.
In adverse weather, outboard and partially exposed container
stacks may be exposed to wind. The degree of force depends on
the velocity and direction of the wind, and the profile of the stacks
affected. The higher the stacks, the greater the surface area and
consequently force generated.
When container ships are exposed to heavy weather, accidents
often involve overturned container stacks in the aft stacks. This is
despite acceleration at the fore end being greater than in the aft.
Aft stack problems
One reason for the problems with aft stacks can be that, due to the
required line of sight from the bridge, stack stowage height aft of
the superstructure is greater than it is to the fore.
Another reason may be that large, wide container ships can suffer
stern slamming when there are following or quartering seas.
This can drastically raise forces on the securing equipment in the
aft container stacks. The intensity of acceleration and forces during
sea transports is affected by different types of seas. Sheltered waters,
shallow seas and deep oceans cause different
levels of acceleration.
Early avoidance essential
To avoid excessive acceleration and forces,
course and speed may have to be adjusted to
ease the shipís motion in heavy seas. Early
avoidance of adverse weather and sea conditions
is always recommended. Taking into account
the actual stability conditions, it may
also be necessary to ballast or de-ballast the
ship, thus improving its behaviour and avoiding
Factors for consideration:
Weather and sea conditions.
- Excessive transverse metacentric height
- Incorrectly stowed containers.
- Overloaded (under-declared) containers.
- Excessive container weight.
- Deteriorated securing equipment.
- Defective container structure.
- Cargo securing arrangements.
- Loss of equipment and containers over
board, lashing by stevedores, positioning
of securing equipment.
Other relevant factors:
- Non-standard securing equipment.
- Improperly maintained securing
- Inadequate supply of correct securing
- Overloading of securing equipment.
Draft, Trim and Heel affecting Hull Strength and Stability of containership
Visibility from Bridge affecting navigation of containership
Propeller immersion affecting navigation of containership
Shearing forces, Bending moments and Torsional moment affecting Hull Strength and Stability of containership
Other factors affecting Hull Strength and Stability as necessary
Other Info Pages
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Container Ship Operation Basic guidance
Cargo stowage and planning How to plan effctively
Cargo care at sea Precautions to be taken
Reefer cargo handling Troubleshoot and countermeasures
Safe Cargo operation and various guidelines
Cargo securing Check items prior departure port
Safe navigation Various factors affecting ships navigation at sea
Hull strength & stability Prior loading how to ensure hull strength & stability of ship
stevedores injury How to prevent injury onboard
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IMO Intact Stability Criterion for containership
Corrected GoM for Hull Strength and Stability of containership
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