Re: Mast Vang

james nolan (nolan_laboratories@email.msn.com)
Sun, 1 Aug 1999 22:05:10 -0600


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West Wight Potter Website at URL
http://www.lesbois.com/wwpotter/
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Doesn't tilting the mast also reduce effective area? Isn't that what happens
when a boat heels? If the lift vector is toward the water rather than
parallel to it isn't the tilting moment vector reduced? If this wasn't so,
sailboats would blow over more easily.
Jim
-----Original Message-----
From: TillyLucy@aol.com <TillyLucy@aol.com>
To: nolan_laboratories@email.msn.com <nolan_laboratories@email.msn.com>;
slithytove@earthlink.net <slithytove@earthlink.net>
Cc: wwpotter@tscnet.com <wwpotter@tscnet.com>
Date: Friday, July 30, 1999 10:19 PM
Subject: Re: Mast Vang

>Geez you guys, I hate to rain on your parade but stop and think for a
>minute.....
>
>The sail is an airfoil and the lift generated is going to be perpendicular
to
>the foil. If you start lengthening the windward shroud, tilting the mast
>towards the water, it's going to have the effect opposite of what you
intend
>- the lift vector is going to be pointing at the water, trying to pull the
>boat over, kind of like an upside down airplane wing.
>
>What you need to do in an "overpower" situation is to reduce the lift
>generated by the sail:
>
>Decrease the angle of attack. This is most easily accomplished on a P-15 by
>letting out the mainsheet. On larger boats where it's necessary to cleat
the
>main, heading up accomplishes the same thing, though it takes you off your
>chosen course.
>
>Decrease the depth of the foil. By flattening the sail you will reduce the
>amount of lift generated. Tighten the outhaul and the downhaul (See Judy
for
>tips on bending the mast to flatten the main)
>
>Reduce sail area. Do the obvious thing, reef!! If you can't reef, lower one
>of the sails.
>
>Please don't take offense, but mankind has been perfecting the design of
>boats for millenia - if there was a free lunch out there, I think it would
>have been found by now.....
>
>
>Best regards,
>
>Dave Kautz
>P-15 #1632 Tilly Lucy
>Palo Alto, CA