We opted for the Rocna 15 (33 lb) on our R-31CB, and are delighted with it. It is larger than the standard recommended for the boat, but the windlass does fine in hauling it up. Fits in the original bow roller with no modification. If you want even more security you might consider a longer chain. We installed 100’ of chain plus the 200’ of rope rode. We felt very secure with this package anchoring all the way up to Skagway Alaska. I give the windlass a rest periodically when weighing anchor, both to let it cool (not sure what the duty cycle is) and to give me opportunity to rearrange the chain in the locker so that it doesn’t jam.
John