how a sail works, who can help me explain?
 

"Simple Simon" wrote in message

Negative a chord is a straight line joining two points on a curve.

This contradicts what you said here...

The convex side of the sail or the leeward side directs the air
over a longer path. This longer path for the air lowers the pressure
because said air must move faster to cover the increased cord.


--
Wally
I demand rigidly-defined areas of uncertainty!
www.art-gallery.myby.co.uk

how a sail works, who can help me explain?
 

I don't hate to say it but you and PIM are BOTH incorrect.

You both have only a laymans idea of how a sail works.

Fact: Venturi effect is proven and accepted
Fact: Venturi effect causes lower pressure in the area of the venturi.
Fact: Lower pressure is cause by the lower density of the gas molecules
in the area.
Fact: An object with low pressure on one side and higher pressure on the
other side if free to move will move in the direction of the low pressure.

THAT is how a sail works. All that other crap is extraneous to the situation
at hand aboard a sailboat. There is no high-horsepower motor available to
make the sail act as a plane like PIM suggests. All the force is generated
by a difference in pressure between the leeward and windward sides of
the sail which force acts against the foil in the water and the planeform
of the hull to produce forward motion.


"jlrogers" wrote in message .com...
I hate to be the one to tell you this, but PIM is correct. Lift is to air as buoyancy is to water.

"Simple Simon" wrote in message ...
I think you should do a little research into Bernouilli and Venturi.


"PIM" wrote in message ...

"Simple Simon" wrote
The convex side of the sail or the leeward side directs the air
over a longer path. This longer path for the air lowers the pressure
because said air must move faster to cover the increased cord.
Faster flow equals lower pressure. This low pressure combined
with the normal or slightly increased pressure on the windward
side is what creates lift.

Dear Simon,
I am not neglecting what happens on the leeward of the sail,
the leeward of the sail is also deflecting air and thereby creating lift.
as I am explaining in www.sailtheory.com/sail.html

According the "longer path theory" you use it would not matter how
much you pull your sail in, since there is always the same difference
in pathlength between windward and leeward.
Please read www.sailtheory.com/wrongtheory.html for more examples
why it is wrong.

The "longer path theory" is not easy to use and is wrong.
It is the reason I started my site.
Clearly I am not clear enough at this point :)

Many agree with me that the longer path theory is wrong:
jeff raskin:
http://tinylink.com/?RD9ntJyTuz
university frankfurt (under 2.2)
http://www.informatik.uni-frankfurt..../MIS/mis6.html
University of washinton:
http://www.aa.washington.edu/faculty/eberhardt/lift.htm
Bill beaty:
http://www.amasci.com/miscon/miscon4.html#wing

And so do the most aerodynamicists as far as I know.

I tried to adjust above theories from a wing into a sail.

Best Regards

Pim






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Posted by news://news.nb.nu

how a sail works, who can help me explain?
 

It does depend on the length difference as stated in the principles
of the venturi effect. The speed of the air is increased when it
is forced through a smaller area. The sail acts like one side of
a venturi in that the air has a smaller area to go through because
of the extra length. The air above that air on the surface of the
foil acts like a venturi also to a small degree. The net effect is
the air moves faster, the molecules become spaced farther apart
and the pressure is decreased. This decreased pressure is a greater
factor causing lift than the air pushing up on the windward side of
the sail.

You might know a lot but you need to learn more when it comes
to the practical application of single-surface foils used on sailboats.

"PIM" wrote in message ...

"Simple Simon" wrote:
I think you should do a little research into Bernouilli and Venturi.

I did, see www.sailtheory.com/bernoulli.html

I am not denying that air goes faster on the leeward,
But it is not depending on the length difference (leeward to windward)

I used to be a Naval Architect/Yacht designer.
Now I am a designer of exhaust systems,
for what you need a lot of aerodynamics.
So I know of Bernoulli.
That I do not use formulas is to make it easy for people who did not study
maths muchs

Best Regards



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Posted by news://news.nb.nu

how a sail works, who can help me explain?
 

Ahah! Now, you've finally gotten to the crux of the matter.

You say diameter is the important thing. You are right
because when you put a venturi into a hose you get
a suction effect at the ventur. The suction proves
lower pressure exists in the area of the venturi.

In the case of a single surface foil the lower pressure
IS caused by the increased length of the surface which
has the effect of making a smaller pipe for the air to
pass through.


"PIM" wrote in message ...

"Simple Simon" wrote
This longer path for the air lowers the pressure
because said air must move faster to cover the increased cord.

The air does not need to speed up to cover the extra length.

When you take a longer way to go home home,
you will just come home later!

same goes for water in a garden hose.
The length of the garden hose does not influence the speed through it.
Diameter and water flow is of importance.
(ok, a really long hose will have so much resistance that the flow will
drop)

Best Regards,
Pim


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Posted by news://news.nb.nu

how a sail works, who can help me explain?
 

"Simple Simon" wrote in message

It's only a contradiction if one chord from leading edge to
trailing edge is envisioned. That is what you envisioned but
your vision is apparently limited. The chord I referred to
is a combination of many small straight lines (chords) that
describe the curve in question.

What a feeble wriggle.


--
Wally
I demand rigidly-defined areas of uncertainty!
www.art-gallery.myby.co.uk

how a sail works, who can help me explain?
 

Hey PUTZ! A misspelled word because of ignorance is
on thing and a misspelled word because of failing to touch
a key hard enough is another.

By the way, your use of vis-a-vis is incorrect as well as
the presentation of it.

It should appear as vis-à-vis.


"Wally" wrote in message ...

Vis-a-vis the use of "cord" instead of "chord"?


--
Wally
I demand rigidly-defined areas of uncertainty!
www.art-gallery.myby.co.uk

how a sail works, who can help me explain?
 

It's called angle of attack. Increase angle of attach to too
great a degree and the telltales will start telling their tales
in in more of a radiating manner.


"Oz1" wrote in message ...
On Mon, 7 Jul 2003 12:37:55 -0400, "Simple Simon"
wrote:

The leeward side of a sail is the side that is convex as opposed
to the windward side which is the side that is concave.

The convex side of the sail or the leeward side directs the air
over a longer path. This longer path for the air lowers the pressure
because said air must move faster to cover the increased cord.
Faster flow equals lower pressure. This low pressure combined
with the normal or slightly increased pressure on the windward
side is what creates lift.

Hmmm can you then eplain why telltales on the concave side of the sail
continue to flow?
One would have to assume that the air to cover a shorter path would be
required to travel in a straight line rather than remain attached to
the curve.


Oz1...of the 3 twins.
I welcome you to crackerbox palace,We've been expecting you.

how a sail works, who can help me explain?
 

"Simple Simon" wrote in message news:wN-

Hey PUTZ!

Neal! Step *away* from the mirror...


A misspelled word because of ignorance is
on thing and a misspelled word because of failing to touch
a key hard enough is another.

And not checking the spelling before posting is the sort of sloppiness you
abhor, isn't it?


--
Wally
I demand rigidly-defined areas of uncertainty!
www.art-gallery.myby.co.uk

how a sail works, who can help me explain?
 

I just translated my dutch website about sail theory into English.
English is not my first language, so if someone can help me to make it
easier to read and help with some nautical words,
that would make me happy.
www.sailtheory.com

If some theory Guru out here could help with the content, He (or She) is
also welcome.

I will not include the latest theories of what deck gun is best.

best regards,

Pim



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Posted by news://news.nb.nu

how a sail works, who can help me explain?
 

You are making a mistake: why the air speeds up at leeward.
It has nothing to do with the length difference.

If you do not want to leave your good old theory,
please consider the one I suggest as an extra.
my theory :
"the sail deflects the air (on the windward side as well as on the leeward
side)"
It is very satisfying, it explains a lot.

Any way, all theories are a simplification of the reality.
more theories to describe the same are possible.
The best theory is the one that is the simplest and explains the most.
It does not mean all other theories are rubbish!

By the way, how do you explain that a flatter sail sails
better "pointing" close hauled as a deep(=curved) sail?
The more curve the more force according your theory, so what is the use of
flattening the sail?
(my answer: www.sailtheory.com/sail.html#ch)


In reply of your previous post:

"Simple Simon" wrote in message
Fact: Venturi effect is proven and accepted
Venturi effect is in a pipe, in a venturi, There it is indeed proven and
accepted.
A sail is no venturi.

Fact: Venturi effect causes lower pressure in the area of the venturi.
yes.

Fact: Lower pressure is cause by the lower density of the gas molecules
in the area.
density difference is not of importance. A keel works just as a sail
prducing sideways lift, but
density of water stays the same.

Fact: An object with low pressure on one side and higher pressure on the
other side if free to move will move in the direction of the low pressure.
Yes.


THAT is how a sail works.
There is no venturi. There is a sail. That is the error.

All that other crap is extraneous to the situation
at hand aboard a sailboat.
oh.

There is no high-horsepower motor available to
make the sail act as a plane like PIM suggests.
I do not want to suggest a motor. Sorry if I did.
(with "power" I mean energy/time, or force x speed, so not a motor,
on my site you can read "force" instead of "power" in most places.
It is a small translation error. "power" is in Dutch different from
"motorpower"
thanks for the hint. This helps improving my site )

All the force is generated
by a difference in pressure between the leeward and
windward sides of the sail
yes, and these pressures are created by changing the direction of the wind
locally.

which force acts against the foil in the water and the planeform
of the hull to produce forward motion.
yes.

Best regards,

Pim
www.sailtheory.com






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Posted by news://news.nb.nu