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Author Topic: Flat sails  (Read 6731 times)
Ken Smith

Posts: 289

sail often, travel light

« on: April 17, 2011, 10:29:21 AM »

Wayne asked (sell folder):

 I am very interested in purchacing one of your sails but I do not know what a speed sail is.  Could you please explain the difference between a jd speed sail and a jd bb01 for me and the rest of the ignorant masses.also could you reccomend the type of  mast which these sails have been designed for (deflection @100lbs)
 please and thanks. wayne matheson

Re the deflection question. Lots of masts are out there with a variety of deflection numbers. These sails would work well on most of them. Mast bend is determined by tuning. Heavy folk and light folk can tune different with the same mast and achieve same or similar mast bend shapes. Lots of other discussions on tuning masts.
Key:  the mast has to bend to go fast. It should be tuned to not bend excessively until the boat lifts a runner at your weight. Wind changes in velocity, tuning may be required.

A speed sail is cut flatter, especially up high. A all- round sail is a little fuller (more curvature) up high and a lot more at the bottom full batten. Speed sails have less low- end power (think acceleration) and less high end drag (warp speed).

The first boat sailed the course at the best VMG, velocity made good- a combination of speed and sailing angle. Sail angle and VMG are solely controlled by the whole boat L/D. Lift over drag ratio. At high drag ice or low wind, full sails are needed. At high wind or fast ice, all sails have too much power, so low drag is desired. Speed sails, being flatter, develop less form drag.

Since sail angles are a function of VMG,

Ken Smith
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