Most C-30 owners would say that 3/8 is perfectly good for all halyards and sheets. Some (like me) use 7/16 on the sheets for a more comfortable "hand" (grip and feel). The use of 1/2 is overkill.What year C30 do you have? My main sheet was 82' with a 7/16" diameter. The jib sheet I use is 1/2" (or some metric equivalent) I think the specs call for 80'. I have a rigging spec sheet for your boat but I can't upload it for some reason. I can email it to you if you send me your email PM.
If he had the lines already he wouldn't be asking us.Most C-30 owners would say that 3/8 is perfectly good for all halyards and sheets. Some (like me) use 7/16 on the sheets for a more comfortable "hand" (grip and feel). The use of 1/2 is overkill.
As far as length, you should just measure what you already have and adjust accordingly.
No confidence in the existing setup versus design specification if available. Also some practical familiarity (local Knowledge) is always helpfulThe jib/genoa sheet can be 1 1/2 times the length of the boat. The main sheet depends on the configuration you have. Why not just measure the old one?
Design spec is a good basis, also practical experience is useful: 1.5xbl for sheets is generic, what if 150% genoa vs trisail ? A storm is the wrong time to adjust your sheets.If he had the lines already he wouldn't be asking us.
There is no such thing as overkill when it comes to comfort.
Stu-the 80' jib sheet length is the longest in the specs. 70' is a jib sheet 80' is for the genoa.
Isosceles showed us that A(squared)+B(squared)=C(squared), the hypotenuse of the 'right triangle'. Therefore the square root of C(squared) plus a length for a knot, five turns around the drum a tail of some length and a stop knot... There, you have it!!! At $1.5 to $4.0 per foot I wish to avoid both spaghetti under foot and chasing the tail up to the sheave when I tack.If you have cheek blocks at the aft end of your cockpit, the sheets will have to be longer. All this is good advice, including my earlier one, but why not simply MEASURE on your boat?
This is a good reason to have a long length of some cheap line - or leftover old line - in your boating kit. Just run the line wherever you will be using it and measure the length needed, then get the good stuff in the size that you want (obviously, don't sail with the junk). For a sail, do this with a very light wind, or no wind....why not simply MEASURE on your boat?