You're probably right, but given that most of us sail with some kind of aft rake, past efforts have shown on almost all classes that if you go from the tip of the bow, the aft measurement ends up behind the boat - not a lot of use! <img src="http://www.catsailor.com/forums/images/graemlins/frown.gif" alt="" />

Therefore cat sailors have established this 'protocol' that the forward trap measurement is always taken at EITHER the bow tang or at the deck above the bow tang in the case of boats with lowered tangs.