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Subject: RE: [worldcruising] Basic Dynamics
From: Andrew Herwig (andrewh@XXX.XXX)
Date: Thu Mar 08 2001 - 19:26:45 EST
Assuming this is a fractional rig, ie the forestay meets below the top of
the mast, bending the mast by increasing backstay tesion simply flattens the
mainsail thereby depowering it. To put shape in the sail when it is made
among other methods, the mainsail is cut flat on the loft floor with a curve
on the luff (mast side). When this flat sail with a curve on it is then
hoisted up the straight mast the excess material has to go somewhere. This
forms a belly aft of the mast thereby giving it an air foil shape. Bending
the mast aft with a backstay pulls some of this belly out and reduces the
draft (and power) of the sail. If you could bend the mast far enough back
you would entirely flatten the sail to the original flat shape laid out on
the loft floor. This would produce little power. This is a very simplistic
explanation but I hope it helps.
Regards
Andrew
> ----------
> From: Luis Gouveia[SMTP:pianinho@XXX.XXX]
> Reply To: worldcruising@XXX.XXX
> Sent: Thursday, 8 March 2001 23:06
> To: worldcruising@XXX.XXX
> Subject: [worldcruising] Basic Dynamics
>
> Hi,
>
> Last time I went sailing (on a First 300), the skipper, a 30
> years-experienced sailor, increased the back-stay tension in order to
> increase the "power" of the sail !?!
>
> I asked him if he didn't mean to say the exact opposite. Which he quickly
> denied. He said: "...when you increase the back-stay tension, bending the
> mast backwards, you're decreasing the distance between the top of the mast
>
> and the foot of the mast, therefore increasing the "roundness" of the
> sail,
> therefore increasing power."
>
> I must admit that he's explanation souns logical, but I must also admit
> that
> I had always thought things happened in the very opposite way: Bending the
>
> mast backwards means decreasing power; straightening the mast means
> increasing the power.
>
> Can you help me out here???
>
> I'm sorry for my bad english terminology, but I only know the portuguese
> terms...
>
> Kind regards,
>
> Luis
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