My sailing buddy (who owns the boat) has a 1970s 18. It has a 28' one piece mast. The main halyard is a single continuous line attached to a ring. We could never get it hooked when fully raised, then pain to unhook. Last year we cut the line and just raised the main without latching it or whatever. It works well when raising and lowering. We will continue to do this now esp since we have to reef often due to unpredictable winds.
The issue is the halyard is very old and stretches something fierce. usually after an hour or so, the boom is so low we have to crawl to the other side when tacking/jibing. I'd like to replace it with some very low stretch line and continue to not use the continuous loop configuration. I can find stuff labeled VLS like this
https://www.murrays.com/product/39-1410/ at about .4 to .8 cents per foot. What diameter should it be? I think 5mm 3/16 and 60 feet. What do you recommend? I don't' want to ask him because it will be a gift for often taking me sailing.