I own a Cal 34 III and would like to know what physical measurements I need to provide to my sailmaker to determine the maximum mainsail roach I can put on my sloop.
Hi Marta, Mainsail roach is described in terms of the sails girth measurements as a per cent of the foot length. There are 4 commonly used girth locations at 25%, 50%, 75% and 87.5% heights along the luff of the sail, starting at the tack. The girths are measured at 90 degrees to the luff.
A mainsail built with a midgirth measurement (girth at 50% of luff length) of 55% (.55* foot length) will clear the backstay without touching on most boats. A mainsail with a midgirth of 65% will generally overlap by a few inches at each of the top 2 or 3 battens. Even larger girths are possible and practical but generally require full battens and you will have to accept that the sail hits the backstay during tacking gybing and hoisting or dropping maneuvers.
Your sailmaker can tell you how much the sail will overlap the backstay at each batten if you provide the following:
* Luff Length
* Foot length
* Distance from back of mast to backstay, measured along the top of the boom.
* Length of masthead crane and height of the crane above the top of the mainsail at full hoist.
I hope this answers your question. Regards, Dan Neri