1/2 is too big for sure. For halyards 7/16 is about right for typical double braid and is what I have now. When I replace, will will go with something hi-tech(spectra or dyneema) , and smaller, probably 3/8. With hi-tech lines you have plenty of strength, you want it large enough to be comfortable in your hand.
My reef lines are 3/8 now, and with hi-tech I would probably stay that size, only because it's too hard to handle line smaller than 3/8.
Thanks Warren, I am glad to think 1/2" is too big as I am finding lots of options for 7/16" with Spectra for reasonable costs and the 1/2" halyards are much more (per foot and come in longer lengths for premade halyards). I really appreciate this forum as I get started with this new-to-me vessel.
I had to replace my two head sail halyards last year. Reason, mice found their way into my mast, not at the base which I cover but through the sheves at the top of the mast. The mast was obviously out of the boat. I replaced both with Dynema ropes from R&W ropes in New Bedford Massachusetts. both are 5/16 for the ability to easily handle it, not for its strength, as Warren says 1/4 inch would be strong enough. I would suggest checking with R&W for a price when you make your selections. They have amazing prices and do ropes for all imaginable applications. Will do splices And mount shackles supplied by you or bought from them. I have no interest in R&W, simply enjoy doing business with them.
interesting aside my halyards are New England ropes. That company was founded by Herb Repass the father of Randy the founder of West Marine.