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Old 01-07-2009, 23:36   #46
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Originally Posted by anotherT34C View Post
Remember that at sea level, and room temperature, the density of air is about 1kg/m^3, while the density of water is about 1000kg/m^3.

Three orders of magnitude is an awful lot.
And that's why keels and sails aren't the same size or shape.

John
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Old 02-07-2009, 04:02   #47
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Additionally, I am not convinced that a symmetrical foil, top and and bottom or in the case of a keel port and starboard, provides much lift especially with such a small angle of attack.
Aerobtic airplanes have symetrical airfoils. They generate lots of lift upside down or rightside up. Often at low angles of attack.

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I suspect those vectors are not the least bit accurate and the diagram neglects that the whole bit is rotated because of heel angle.
The more heeled the boat is the more leway is given up. Sail flat!

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If you can't relate to my windsurfer story, try it on a dinghy like a Laser. Grab the boom with your hand and pull the sail to weather and head up from sailing close hauled.
Alternately, in light air, get the dinghy stablized close hauled and lift the daggerboard.

If the airs aren't light you'll practice capsize drill. If you keep the dinghy right side up you will definitely be sailing sideways.
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Old 02-07-2009, 06:37   #48
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Originally Posted by cal40john

If you can't relate to my windsurfer story, try it on a dinghy like a Laser. Grab the boom with your hand and pull the sail to weather and head up from sailing close hauled.




Alternately, in light air, get the dinghy stablized close hauled and lift the daggerboard.

If the airs aren't light you'll practice capsize drill. If you keep the dinghy right side up you will definitely be sailing sideways.
What I wanted people to see with my experiment was that even with the daggerboard down, the boat will slide sideways surprisingly quickly if there is no attached flow (lift). The surface area of the blade being dragged sideways through the water makes a lot less drag than you would think if you're used to how little leeway you make when the blade is making lift.


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Old 03-07-2009, 12:45   #49
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Here's a great video that hits it right on the head: The Physics of Sailing - KQED QUEST Television Story

Great video link! Put it all together nicely for me....

I remember reading somewhere what a sailboat should be able to acheive 2x the wind speed when sailing with the wind?

Anyway, all of this is a moot point.

This is how you sail:

Drop the sails, fire up the 90 hp outboard on your macgregor, get to point B, have beer.

jk
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