Thanks for the comments. I saw the same drawing from the F18 rules but since I don't have the boat to measure beam-to-bow, I didnt' know if a pole should be 11, 12, 13, or 14 feet. The 3600 mm number puts it right close to 12 feet, just the length of the pole I have. I won't be sailing F18, I just want to find a modern used (cheap) F18 spin and not struggle with geometries too much. There seems to be no easy way to sneak into the spin world without hurling money at it.