Here's a passage from 1 manufacturer as to why:
"there should not be so much line on the drum that it binds against the drum cover when fully wound for any particular sail. Start with the sail rolled up. There should not be more than 3 wraps on the drum when the sail is tightly furled with the sheets wrapped around it twice. If you cannot get enough line on the drum to completely unfurl the sail, then the line you are using is too large. Reduce line size or, remove the core in the forward third of a braided line. "Coring" the line will reduce the amount of space it takes up and cause it to lie flatter on the drum. This should be done in all furling installations using standard braided line, as it reduces fouling and overrides while still giving you a full diameter line in the cockpit." You will need to cut the line with knife so it's not heat sealed, put tape around outer braid so it don't unravel,pull core from outer braid for appropriate length & cut core using heat to seal. Pull outer braid back over and seal end with heat. Some take a few stitchs thru core & cover where core ends to keep them from slipping but I have not found that necessary. I've used Sta-Set for furling line and it's probably 5/16 or 3/8 for your boat.
