That is the mainsheet fine tune. There is a 6:1 purchase inside the boom that allows the main to be trimmed easily, for upwind trimming. The added purchse is very helpful for controlling leach twist in medium to heavy air.
I believe this is standard on the 37/40R and was an option on the XL. Hope this helps. Bruno Mannsberger C&C 37/40 R Wave Train Ladysmith BC
_______________________________________________ This list is supported by the generous donations of our members. If you like what we do, please help us pay for our costs by donating. All Contributions are greatly appreciated!
