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Boat sails

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RBosque

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RBosque, good luck to you and your friends.

I'd like to digress off-topic for a moment. For the last 20+ years I've been working on the flapping flight mechanics of articulated high aspect ratio extensible tension battened membrane wings. There are some similarities and a LOT of differences to the somewhat inextensible sail materials you guys use. At your convenience, I'd like to chat with you by PM about the methods and techniques you guys use to adjust the chordwise and spanwise progression of your sail camber and your control of the tendency for the line of maximum camber to progress aftward along the chord toward the trailing edge with increasing speed. I'm looking for informed advice and do not intend to presume to offer suggestions to you guys. Basically, I'm interested in delaying and inhibiting the onset of local flutter due to declining aeroelastic number as the lift coefficient decreases with increasing speed.
Thanks,
Jim

Back on topic - my family unit of six is currently self quarantined near Augusta, GA (where there are currently two confirmed Covid-19 cases and one probable). We have no known exposure - just being cautious. At the end of the week three of us will relocate to the Memphis area (to return my grandson to his dad), and will continue to self quarantine there.

I am somewhat concerned about looking after my disabled brother who lives alone two hours from me in southeast Arkansas. I'm the only one he's got, and I see no way to cover for him without going to see him once or twice a week.
I wish the absolute best for you and your family and fully understand your concerns. It sounds to me like you're taking all the reasonable precautions that can be taken. As to sail control, I'll give you a brief rundown, even though it's off-topic.

We control sail shape by adjusting tension in the luff, leech and foot of the sails, as well as by bending the mast in the case of sails whose luffa are attached to a mast. Of course, the sails are cut in such a way as to make our adjustments work. The main aspects we want to control are:

1.) The draft of the sail (how curved or flat it).
2.) The position of the draft (where the maximum "curvature" of the sail is).
3.) The twist of the sail (how the angle of the sail changes in relation to the centerline of the boat and the speed and direction of the relative wind in proportion to the height of the sail).

By controlling the shape of the sails, we control the amount of "lift" they generate when they are in "lift mode" (sailing to windward) and how much drag they create when they are in "drag mode" (sailing downwind) and thus the amount of power available to the boat. This also controls where the "center of effort" (the sum of the lift or drag created by all the sails) is in relation to the "center of lateral resistance" (the "lift" generated by the keel). It's part art and part science. Honestly, we mostly "eyeball it" and "feel it" based on experience. Of course, we do have instrumentation that quantifies any adjustments we make so that we're not fooled by our senses. That's pretty much all there is to it.

You might want to ask some sailmakers about the cut and shape of sails. North Sails is probably one of the most technically advanced sailmakers.
 

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