Safety Factor

By Will van 't Hek

Using safety factors to lash and secure loads is getting out of hand. Companies use it to increase their safety in load-outs, or is it because they are not sure of themselves?

When cargo is loaded onto a vessel according IMO Annex 13, acceleration factors will be taken from a table or calculated by using formulas. The achieved lashing acceleration is always very high. This is done to have a single guideline for all sort of vessels. However, if you engineer the acceleration forces they are always a lot less than the IMO. According IMO this is done to add safety in the load-out. Understandable. Now we have to lash and secure the cargo against various forces and when using a chain we can only use 50% of the MBL (Maximum break load), again for safety. Then after this 50%, we again have to apply a lashing safety factor of 1.35 or 1.5 to obtain a calculated strength (CS). Why? Again for safety.

In reality, this means that if you have a chain of 200kN break load, you only have 100kN in MSL (Maximum Securing Load). Again, you have to apply a factor of 1.35 to obtain the calculated strength. This brings the chain back to 74kN. If this chain is applied in transverse direction with an angle of 45 degrees, you will get the following equation 74 x (Cos 45 = 0.707) = 52.3kN what can be used…

Now, using a GP shackle of 85tons SWL for lifting, you can only use it for 85tons. A factor 5 is applied to retrieve the break load so. 85 x 5 = 425tons Break load. When the same shackle is used for lashing & securing, we can use 50% of the break load which is 212.5tons. The safety factor is used in many ways, WLL, MSL, SWL, break load. When it gets to offshore safety it flies to the top. Safety on safety on safety.

BargingLashing & securing


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