Submitted on October 22, 2001 by Marta Roque

Question: 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.

Answer: 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. At North Sails we have predefined cruising mainsail roach profiles with midgirth measurements of approximately 55%, 64%, 71% and 77%. The largest roach profiles are only available on full batten mainsails.

With your input, your North Sails rep will specify one of these 4 profiles, in order to identify the range of sail area and backstay overlap you are looking for. Then the sail design staff will adjust the roach profile depending on the aspect ratio of your sailplan and the position of the backstay relative to the boom end and masthead. The mainsail measurement form includes all the information that the sail designers need for these calculations. The basic information needed to determine the amount that the mainsail will overlap the backstay at each batten includes 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

Email North Sails with your question today!

Go BACK to Solutions for Sailors Main Page.