Mark Ayers

JH, I would use the originial blocks as a reference for size/ ratio. the Fiddle blocks should be easy to locate and the measurements are going to mostly relate to line size. Sheave diameter will affect your ratio, but distance between the sheaves should not. Most sheaves should have a max line size. On the Blocks, you can always go up in value, for example if you have 3:1 blocks you can always go to 4:1 it will require slightly more line, but will be easier to sheet in, and give you more power, but if you go down for example from 3:1 to 2:1 you can sheet in faster with less line, but your power goes down and effort goes up. Line size is really a personal preference as long as the working load is within range of what your boat needs. In either case, your original blocks should be a good place to start. I hope this helps Mark