How to calculate Lashing Strength onboard container ships
Lashing strength of deck cargo shall be ascertained by using the appropriate lashing strength calculation software where provided.
All resulting values for lashing strength must be within the tolerance limits prescribed by vessels classification society.
Lashing strength calculation software provides alarms/highlights for containers that are affected by excessive forces. Such situation may be corrected by adjusting the vessels Ballast / Fuel condition or alternatively by advising Terminal planner / Central planner and having the cargo stow plan appropriately modified.
In case such anomaly is noticed, the master shall notify all concerned parties and have the condition corrected at the earliest prior departure or at the next port as instructed by Vessel operator / Central planner. In such case, master shall also take this special case into account during maneuvering in heavy weather.
If lashing strength calculation results are exceeding tolerance limits, failure of lashing gear or failure of the container itself may occur. Probability of this happening is highly enhanced in inclement weather and attendant heavy rolling, pitching or heaving.
Each lashing gear component has a safe working load and is likely to fail if forces exceed this value. Failure of lashing gear components will then besides freeing restraints, also likely result in forces on containers exceeding tolerance limits.
Sea freight containers are designed to withstand a defined minimum racking force, side wall racking force, vertical compression, vertical tension, corner post and shearing force at twist lock.
Forces exceeding these defined minimum values (tolerance limits) will likely result in structural damage or collapse of the container. If one container in a stack collapses, it is likely that the entire stack will collapse.
Other factors should be taken into account before accepting a containership cargo stowage plan, :
Stacking Weights
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
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