Do telltales tell all?
james nolan (nolan_laboratories@email.msn.com)
Tue, 27 Jul 1999 22:33:15 -0600
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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