Variables
Hi there,
Your inner engineer is far too easily appeased. "Hasn't broke yet" is not engineering, though in this case the rope size is right. Regarding this and the previous thread, knowing what the load is and responding appropriately is a good working definition of good rigging.
For sheets, the loads are highest when the runs are shortest, so elasticity, while it matters, is less of an issue than with halyards; handling, and dealing with shock loads matter more. Also, it is a bit erroneous to think purely in terms of tensile strength; what matters more is that the design load (typical working load) is a fairly small (20% or less) percentage of the tensile strength. This is not to provide a safety factor, but to keep elasticity down. That's why you can usually afford to tie knots in sheets. The result also usually happens to be a line that is comfortable to hold, but diameter is something to engineer in, as there are lots of lines that will be absurdly strong, and too (shock loads) inelastic if they're comfy to hold.
I can't stress it enough: run the numbers. Play them off against cost, handling, elasticity, strength, and any other variables that you can think of. Block and winch selection, as well as rope selection, can then be rational exercises.
Fair leads,
Brion Toss
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