21.4cm circumference, 0.6cm rope would need 210/.6=350 turns at 21.4cm each=7490/100=75m?
Sounds reasonable to me. You have assumed you have a minimal helix angle, but that seems like a good assumption to make. I'd get yourself some spare too of course, just in case...
@hamrack started
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21.4cm circumference, 0.6cm rope would need 210/.6=350 turns at 21.4cm each=7490/100=75m?