I forgot to mention that F16's are up to 16'5" long. As for main beam location the length of your mainsail foot will be a significant factor as the longer it is the further forward the main beam will have to be moved. So as previously mentioned have a quick check on the F16 website for sail dimensions (I hope you'll find them). <img src="http://www.catsailor.com/forums/images/graemlins/confused.gif" alt="" />