Bill Longyard
Winston-Salem, NC
james nolan wrote:
>
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> West Wight Potter Website at URL
> http://www.lesbois.com/wwpotter/
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> I've been looking at the telltale system for sails and been scratching my
> head. People have been adjusting the sails so that the telltales are about
> to droop. All this shows is a stalled air flow on one side of the sail.
> Isn't it better to adjust the sail for maximum pressure differential between
> the two sides of the sail? To measure this one could simply use what is
> known as a differential water manometer. They cost about $20 and are used to
> measure the pressure drop across air filters in building air conditioners.
> I've used them to measure pressure differentials smaller than .05 inches of
> water. All you would need to do is install a series of small diameter tubing
> to the luff of the sail on opposite sides and run the tubes to a Leur
> fitting manifold in the cockpit. You would then switch in the correct pairs
> of tubing to measure the pressure differential across the sail. To even
> further enhance the system, a strain gauge (or simply a fish weighing scale)
> could be attached in series with the backstay. The backstay tension would be
> proportional to the forward drive of the sail. You would want to adjust the
> sail then for maximum pressure differential on the manometer and maximum
> backstay tension on the fish scale. For less than $100 you could have a
> precision sail monitoring system that would even make Rube Goldberg
> jealous. Are systems like this used on racing boats?
>
> Jim Nolan