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Sail trim for rookies
Ahoy, Art. Keep the wing concept stuck in your head. The sail and the wing operate on the same principle, the Bornoulli effect. Notice, as existence, that some planes (planes on the air) use sails, and some boats use wings.
May I muse?
I attach the following:
RichH: ...light weight sheets....
(Jeff agreed. I concurr.)
JeffH: You sometimes do better
sailing a hot reaching angle
flying a light, flat cut
JeffH: ...you can get outrageous
gradient phenominas and so
twist becomes critical.
The bag concept holds for light air. The bag, though constructed of light material, is heavy. It is matter. It takes a weight greater than its own weight to alter its inertia. Some weight must hold it up and press it into shape before it can be an air foil per Bernoulli. Then, airflow over it must produce lift.
It isn''t that there is something wrong with the concept assymetrical spinnaker. In certain conditions, they are excellent.
It is, just as we always underestimate the impact of an increase in wind speed, we always underestimate the impact of the decrease as the wind speed deminishes.
All that running around and bobbing up and down and rolling to and fro is disturbing both the air and the water. IN VERY LIGHT AIR, EFFICIENCY IS PREMIUM. As another indicated, you need the same shape main (and Jeff about the Genoa) that you need for heavier air. Very light air is very light because it has very little weight. It has very little weight because it is either not dense (warm air), or it has little velocity (cold air). Strong systems are highly energetic, but that are also, highly stable. Very light systems have little energy, and little weight, and are therefore easily disturbed.
Also, if I bubble a part of the sail and it begins to bellow, it will have to life dead sail to expand.
Next, the wind strikes a convex surface at the edges first. This tends to straighten the convex, bringing it square to the wind, increasing the area perpendicular to the wind. If I have a flat sail,trimed square to the wind in a calm, the first air will hit it flush, billow the sail easily, and, if the sheets do not cause drag, will push the sail into position and shape quickly.
If you are racing in very light air, accelerators have advantage. It is making hay while the sun shines. I don''t like assymetricals in very light air.
Prior to conclusion: (Jeff will not like this, I am sure, but I found it useful.)
Recall that if the center of effort of the sails is forward of the center of later resistance of the hull, the boat will wind-vane down by the bow - now the larger push - causing lee helm. Recall that heeling places the drive of the sails outside the centerline of the boat, adding turning moment, as the heel changes the underwater shape of the boat, summing to a tendency to head up.
I like to add a slight forward bend in the mast, moving the center of effort forward just a little. I balace that against heel. I strive for the heeling effect (turn up) to balance the pushing off effect of moving the coe forward, producing no helm,eliminating that drag.