Tom-
I'm not sure which windlass you have there, maybe a Lewmar V-700?
But anyway, most all of those suitably sized for a C-Dory 19, 22, 25, or TC are set up with the chain/rope gypsy set up for 1/2" nylon three strand line, or something very similar in texture and stiffness.
A line too small or too large will not fit in the "V" that also forms the chain link pockets. Either may slip.
Too soft a line will jam in the V, creating a snarl, and too stiff a line can simply slip, or jump out of the down turning entrance port to the locker below.
Lewmar sells, through various marine dealers, ready-made rope/chain rodes that are the proper stiffness and have splices that pass through the gypsy on the windlass pretty well.
I like to make my own out of New England Ropes (from West Marine) Premium 1/2" three strand Nylon Yacht Braid. I made my own type of splice to avoid the big "wad" that is typical of the most common (back-splicing) splicing technique, but have never really tested it under extreme conditions. It discussed
HERE.
They (WM) also have their own ready-made, pre-spliced rope/chain rodes for windlasses. You can return it if it doesn't work, at least!
Most of these windlasses when sold in the US, also have their chain pockets sized for 1/4" GS 40 High Test Marine Grade (hot zinc dipped) chain. The chain must fit the pockets, period! A few have gypsies that will also or otherwise accept BBB, Proof Coil, or other grade chain. Special gypsies can also be ordered for special needs. Windlasses sold in Europe and other parts of the world my have different gypsies, often sized for metric rope and chain, although gypsies can sometimes be designed to fit both metric and English sized rode components.
For exact recommended rope/chain requirements, look at the instructions that came with the windlass, and/or call the technical rep listed at the manufacturer's/importers website or manual. I prefer to talk directly to them, myself, and while email also works, it is definitely slower for a lot of give and take type of questions.
You can also just put chain in the windlass for the test, of course. Just be sure you've laid it out to cleanly feed into the windlass and that the tail of the incoming chain has somewhere to go!
Have fun with your project! Nice talking with you!
Joe. :teeth :thup