It seems like this:
- The lashing capacity LC according to the norm (EN 12195-2) means the maximum allowed force on the strap in straight pull.
- When buying lashing straps, you might get an additional second LC measure that is double of the normal LC. This is the lashing capacity in round pull.
- Why is round pull LC double that of straight pull LC? Think of an application where you connect two points have 180° deflection of the lashing strap (around a tube or similar) at each, in effect making the lashing strap go a full round. A model for this is a small set of pulleys with two barrels and double string. Each of the strings of the one lashing strap (one going forward, the other going back) now has only to bear half of the force between these two points that you pull together, which doubles the lashing capacity compared to straight pull. And as in a pulley system, the force on the belt is the same everywhere as it can distribute evenly, so the part in the 180° deflection point also bears just half the load of the full system.
- To make the confusion complete, there is a code concerning straight line seams on the lashing straps. They are called “ton lines” (German: Tonnenstreifen) and people think that they indicate: one stripe per 1000 daN lashing capacity in round pull (not in straight pull). But I have yet to see the norm text for that and could not find any source (Hey regulators! You still don’t have these as open content? C’m on, nobody wants to pay 224 USD for the EN 12195-2). In case of lifting loops, they are called “load bearing capacity stripes” (German: Tragfähigkeitsstreifen) and there, indeed, one stripe seems to mean 1000 kg of capacity, but in direct pull.
See also another (German) site with explanations of the lashing strap norm’s abbreviations (LC, HF, SHF, STF, BF, BFmin).
Before using information in this text for security critical applications, check the facts for yourself. I do not take any responsibility!