how a sail works, who can help me explain?
 

"Simple Simon" wrote
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.
I agree.
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.
No, there is no real smaller area.
The air above that air on the surface of the
foil acts like a venturi also to a small degree.

!!The distance of the leeward and windward part of the sail is the same!!
only when you have some distance from the sail you have some
length difference because of taking the "inner turn" !
This means the further away from the sail the bigger the lenght difference
so the more the speed difference?
I do not think so.

The net effect is
the air moves faster, the molecules become spaced farther apart
and the pressure is decreased.
the molecules being spaced further apart are no issue.
A wing, sail, or keel can also produce lift under water, and water can not
be compressed.

This decreased pressure is a greater
factor causing lift than the air pushing up on the windward side of
the sail.
Why?

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.
Practical application of sails: I am always learning to become better in
sailing.
Theoretical: I rule :-)

Best regards,
Pim


--
Posted by news://news.nb.nu

how a sail works, who can help me explain?
 

"Simple Simon" wrote in message

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

Never once did I claim to abhor misspelling.

I didn't say you had. It was an example of sloppiness, and I believe I'm
right in saying that sloppiness is something that you can't abide. The key
phrase was "... is the sort of sloppiness ...".


I simply stated
that in a published work done at the college level

I don't recall you saying "in a published work done at the college level".


... one would
tend to doubt the credibility and accuracy of an author who
misspells the very topic upon which he expounds.

I think that doubting the credibility and accuracy of an author should be
based on the truth or otherwise of his premises, and the logical validity of
his arguments.


And, I did check the spelling with the spell checker but it
just so happens that both chord and cord are words
correctly spelled.

What on earth are you using a spell checker for?? Those things are rubbish!
As you ably demonstrated but a few posts ago!


What's your excuse for vis-a-vis?

I don't speak French, my keyboard doesn't have squggly characters readily to
hand, and I don't particularly give a ****.


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

how a sail works, who can help me explain?
 

"Simple Simon" wrote in message
...
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.


If I didn't already know the answer, I'd be tempted to measure both sides
of my mainsail - to see if you were right.

Fortunately, I am not stupid enough to think that there is a significant
difference between the lengths of the windward and leeward surfaces. Where
do you get this rubbish from? Are you reading a "definitive" book on the
subject?



Regards


Donal
--

how a sail works, who can help me explain?
 

"Wally" wrote in message
...
"Simple Simon" wrote in message

I think an incorrect spelling of an important name serves
to notify the reader that the writer is not very careful or
observant. Both are attributes that cause doubt as to the
veracity of the author's work.

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

Correction - You should have said -
"cord" instead of "an infinite series of chords".



Regards


Donal
--

how a sail works, who can help me explain?
 

"Wally" wrote in message news:tbnOa.4848

But the air on each side behaves differently, does it not? On the leeward
side, it's passing over a convex shape, on the windward, is it getting
fouled inside a concave shape? If so, isn't there a case for saying that
the
air within the convex

Brain slip - should be "... air within the concave ..."


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

how a sail works, who can help me explain?
 

Your theory is just not complete.

And, to deny an object shaped like a venturi does not act
like a venturi is not logical. Just because one generally thinks
of a venturi as a tube like in a carburetor it does not mean
that a venturi can only be a tube. Air passing over the
restriction does not care if it is circular of flattened out.





"PIM" wrote in message ...
A single surface sail has the same length on leeward as on the windward
side.
so there IS NO increased length of the surface.

I am not denying a Venturi,
I am denying that a sail acts as a venturi.

Anyway, what is wrong with my theory ?
it offers a good explanation of what is happening.

Best Regards,

Pim
www.sailtheory.com


"Simple Simon" wrote:
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.


--
Posted by news://news.nb.nu

how a sail works, who can help me explain?
 

Some things may remain unsaid especially for those
too lazy to read the material in question. One cannot
spend all one's time complicating a discussion by
including everything some reader may have missed.

If you had visited the links that were being discussed
you would have known. Had you just examimed the
links alone without visiting them you would have
seen that a couple of them were colleges.

"Wally" wrote in message ...

I don't recall you saying "in a published work done at the college level".

how a sail works, who can help me explain?
 

"Simple Simon" wrote in message news:ie-

Some things may remain unsaid especially for those
too lazy to read the material in question. One cannot
spend all one's time complicating a discussion by
including everything some reader may have missed.

If you had visited the links that were being discussed
you would have known. Had you just examimed the
links alone without visiting them you would have
seen that a couple of them were colleges.

Gosh. So they were...


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

how a sail works, who can help me explain?
 

"PIM" wrote in message ...
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)

You forget an important concept that of drag. A foil
is a compromise between lift and drag. NACA did
extensive studies on differently shaped foils and it
was all about lift vs.drag. One can make a foil with
maximum lift but if it also has maximum drag it will
not function very well. If a foil is to full in higher
winds it creates more drag. a flatter foil creates
less lift but proportionately less drag so overall
it is more efficient.

A sail is no venturi.

Yes it is. Take a venturi. Cut it and unroll it so it is spread out.
It is still a venturi but just not a cylindrical venturi. Air molecules
don't know if they are passing over a curve in a closed cylinder
or a curve in a spread out cylinder. View the sail as a spread
out cylinder.

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.

Density is all important because things happen on a molecular
level. It is a fact of physics that lower density equals lower
pressure. The measure of pressure of a gas tells you its
density.

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.

Incorrect as explained above with respect to the opened
and spread out cylinder and how molecules of air see no
difference.

how a sail works, who can help me explain?
 

You're as bad as PIM in forgetting what angle of attach
does to the lengths of the sides of single sided foil. Think
of the distance the air molecules must move on the leeward
side as opposed to the windward side.

The nice curves indicating the movement of individual air
molecules demonstrate this nicely. Measure them and
see for yourself. Print it out and use a divider. You will
be surprised.
"Donal" wrote in message ...

"Simple Simon" wrote in message
...
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.


If I didn't already know the answer, I'd be tempted to measure both sides
of my mainsail - to see if you were right.

Fortunately, I am not stupid enough to think that there is a significant
difference between the lengths of the windward and leeward surfaces. Where
do you get this rubbish from? Are you reading a "definitive" book on the
subject?



Regards


Donal
--