75%/25% skew load for 4 point lifts

[TheJing]

When there is a 4-point lift, you need to account for skew loads due to sling length inaccuracies etc. Sometimes a 75/25% split in sling forces is used. It's been 15 years since I've done such a calc and I'm looking for a reference to the 75/25 split and _only_ the 75/25 split. I know about the API 2A factor of 2 or the DNV factor of 1.25 but in this case it is a reference to the 75/25 split which I'm after.

It's the same 75/25 split that this guy is talking about

http://www.eng-tips.com/viewthread.cfm?qid=215491

I remember reading this 75/25 factor in a design code but I just can't remember which design code. Does anybody know?

 

[Ussuri]

I cannot think I have seen it written in a code before. It is mentioned in Chakrabarti's Handbook of Offshore Engineering on p 1107, but it doesn't give a reference. It does give references for the other methods though.

 

[BMart006]

We typically simplify matters to use a 50%/50% split between two slings; though this sometimes can be unnecessarily conservative at times, more often than not the differences in sling sizes (talking wire rope diameter, synthetic sling size, etc.) is not significant. Typically the forces to the structure being lifted controls. If it is of great importance to reduce the sling loads, you can use a flounder plate or other equalizing method so everything distributes evenly (neglecting friction in hardware).