Your theory is just too simple even for Simple Simon.

You cannot just take one side of a sail and claim it does
all the work. There is much more to it than that. If your
simple theory was correct all one would need is sheets
of plywood set at an angle to the wind and sailboats
would go just as fast as those with dacron sails that
are cut to produce the correct shape to cause the
venturi effect to produce lift.


"PIM" wrote in message ...
I did not really leave the discussion completely, it was just a slip of the
keybord when I was too irritated about a stupid theory that is based on:
"things on a longer path go faster"
combined with some quicktime videos that did not work
My emotion took over. :-(

And I am always lurking.

Thanks,

Pim
who knows the theory on
www.sailtheory.com
is better as simple mc neals "Ventulli" theory.


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

PIM,

I for one, hope you stick around. You are an asset to the group.

We may be a bit Harsh in reply but; "we call'em as we see'em!" I kind of
like it that way. We do have probably more than our share of asshole but
that is to be expected in an unmoderated group. They can be ignored and
and sometimes played with.

You, though have something to contribute. Hang around and get to know
us. We liken ourselves to a cross section of a public bar, where
everyone is allowed to have an opinion (Good or Bad)

AND NOW; Your posting. Bernoulli is incomplete as far as sail function
is concern. So is Newton. That is why the designers use Coanda and
circulation.
You as much said there are voids in the Theories, and you're right.
Remember humans were using sails centuries before Bernoulli and Newton
were born and they designed and used some pretty different sails that
worked well. Damn well. Those that come to mind; The Vikings, Egyptian,
Polynesians, the traders in the Indian Ocean and China Seas. They had
square sails, fore and aft Lateen and Junk sails,Claw Sails and a
triangular sail on the Nile before Christ was born. It get hard ,
sometimes to remember the sails came first and the theories much later.
It's no wonder these theories are incomplete. The thinkers didn't have
sail in mind and certainly not wings.

I do believe that all theories, though incomplete, if usable should not
be abandon. Bernoulli works well for sailboaters but fall way short on
Hvy Than Aircraft. With powered flight even Newton's Laws need
modification. I truly don't see a need for Newton's 2nd Law; (Lift=mA)
in sailing

So, in conclusion let's use what works for us and keep all that applies

Stick with us, you thick headed Dutchman, I'm getting to like you

AND: "I'LL DRINK TO THAT!"

Ole Thom
SV "Pneuma"
Gulf 29 Pilothouse Sloop

"PIM" wrote in message ...
"Simple Simon" wrote:
The prime motive force occurs on the leeward side of the
sail and not on the windward side as PIM is attempting
to suggest.
I am not suggsting that the sailforce comes from the windward side alone,
The leeward side is also very effective in deflecting the wind.
(Actually I suggest the leeward side is a little more important, because
there is more air on the leeward, because it has been sucked to the leeward
side.)
again, this is on my website under www.sailtheory.com/sail.html

And why is it sucked to leeward? Because it causes a vacuum and nature
abhores a vacuum, thus it sucks the sail forward.

Capt. Dowra,ESQ

Guess thats why you get sucked aground eh?

Cheers MC

dowra wrote:





And why is it sucked to leeward? Because it causes a vacuum and nature
abhores a vacuum, thus it sucks the sail forward.

Capt. Dowra,ESQ

We are talking about a sail which is a single-surface foil here.
Proof that the Venturi effect is what provides the lion's share
of the lift in the system is the fact that the sail is shaped
by the pressures on either side. Because the sail's convex side is
always facing the area of lowest pressure proves the venturi effect
is in action. (This is not true only on a dead run where the shape is
caused by wind action on the windward side of the sail)


Professor em. of Physics Weltner shows here how misunderstood
Bernoulli equation can be:

http://www.rz.uni-frankfurt.de/~weltner/Mis6/mis6.html

The good professor is confusing a descriptive term (longer path)
for a causative agent (lower pressure). The longer path is not the
cause of the lower pressure. The lower pressure is caused by the
speeding up of the air molecules because of the SHAPE of the path.
Use the wrong shape and you will not get lowered pressure.

When it comes to producing low pressure there is no wrong shape.
Pressure differentials are a characteristic of lift and dynamic drag.
What shape object wrong or otherwise does not generate an area of low
pressure when moving thru the air? Low pressure is simply caused by a
solid object (regardless of its shape) in a relative airflow. Low
pressure alone does little to cause lift. Low pressure from a relative
airflow does little to pull or suck the solid object or allow the
higher pressure to push the object in the direction of the low
pressure.
The shape of the object allows this low pressure to generate a
substantial amount of lift. This is very easy to prove.

The
shape is the key to lowering the pressure efficiently and without
excess drag - not the longer path.

Because the shape confers a longer path does not mean it is the longer
path that is the cause. The shape of the foil is important not the longer
path. The so-called longer path descriptor is ONLY a descriptor.
This seems to go over the heads of so many professorial types who
are all too involved with nomenclature.


Aerodynamist Martin Ingelman-Sundberg ownsite with articles :

http://www.marv.nu/undersajtm.html

And, this chap is talking only of airplanes and probably has never
sailed in his life and is also unfamiliar with single-sided foils that
are shaped by the wind.

Thanks for the links but I still know I'm right when it comes to
sailboats.

Capt. Neal
http://www.homestead.com/captneal/index.html

~~~~~~~~~~~~~

Why? Do you have experience getting sucked off by men?
You keep mentioning this sort of thing, and eventually one
begins to wonder. Why not just admit you're gay. I'm sure
you can find like-minded individuals in Florida.

"Simple Simon" wrote in message
...

"Oz1" wrote in message
...
On Thu, 10 Jul 2003 15:05:41 +1200, The_navigator_©
wrote:

Guess thats why you get sucked aground eh?

Cheers MC

Nah, that's Ground Effect!


Well, knock me over with a feather. I thought getting
sucked around was the GANZ effect.

PIM,

You asked for help in explaining your description of the action of a
sail and we only gave you negative comments. Let me give a try to put
you thoughts into my words and we'll let Neal pick at both of us.

It isn't going to be easy as sailors have always gotten good results
with sailing by tell-tales and stream lined flows and the Bernoulli
Theorem;
But, let's give it a try------

So, the difference in your thoughts is that the sail pushes the boat by
using the reaction of the action caused by the bending of the air on the
curved lee side of the sail. ( Action and Reaction)

This happens by the curved sail passing thru the air, or more precisely,
the air passing around the curved sail. The action being the bending
back of the air causing a drafting effect towards the windward side of
the sail. This action, created by curved section creates a reaction to
the windward side of the sail causing a drafting force to push the sail
and the boat. With the help of the Keel this reactive force is converted
to an angular force driving the boat forward.

Now, why does this happen? The cause of this leeward action is the
DEFLECTION of the air away from the curve leeward side of the sail.
This deflection creates a void which causes the air in front of the sail
to rush into the void created by the deflected air. This in turn creates
the backward draft that creates the reactive. equal and opposite,
forward draft on the windward side of the sail. This is the pressure
that drives the boat forward

Does that sound correct, PIM? That would satisfy the tell-tales and give
reason for the upper windward tell-tale to be dancing as tell-tale
sailor know is sailing in the "GROVE"

The only difference now is we are using positive pressure to push rather
negative pressure to pull. We still create a higher velocity of air on
the lee side but replace it with new air, which doesn't have to accept
the Equal Transit Time

I hope you notice I made no mention of a wing!

OK! I'm ready for the flaming replies

Ole Thom

Kinda makes sense in a way.... I had full battens installed a few years ago
on my bagged main and noticed a big difference in point and speed.

The full battens induce a nice curve even in the lightest air.

CM


"PIM" wrote in message ...
| I am suggesting a curved plate works better!

"Simple Simon" wrote in message ...
"Oz1" wrote in message ...
On Thu, 10 Jul 2003 15:05:41 +1200, The_navigator_©
wrote:

Guess thats why you get sucked aground eh?

Cheers MC

Nah, that's Ground Effect!


Well, knock me over with a feather. I thought getting
sucked around was the GANZ effect.

Your moniker says it all!
Simple salutations, DOWRA(Superior)

"PIM" wrote in message ...
"Simple Simon" wrote:
That's precisely why I give more credence to Venturi.

I like to keep it simple as my name suggests. Why
clutter a good physical reality with extra theories
that may or may not be applicable?

In my opinion the theory:
"air tends to follow the sail (also on the leeward),
and thus deflects the air, and for that deflection you need a force,
and that force is the sailforce"

is easier as explaining:
"the path on the leeward is longer, so the air has to move faster"
continued with
"fast moving air has a lower pressure"
"just like in a venturi in a pipe"

Please note that I do not make air molecules bounce of the sail,
I am deflecting a flow of air.
To check if that flow has not separated from the sail I also reccomend
telltales.

Please read www.sailtheory.com/sail.html for more details.

What might be confusing:
Bernoulli never had a theory for a wing. He had a theory for explaining how
high a fountain would spray.
Newton never had a theory for a wing, his theory was about bouncing balls
and planets etc.
Euler, Kutta and Joukofski, and Prandtl all had some theories about flow
around a wing.
For some strange reasons they are not often mentioned.
(I am promoting Ludwigs Prandtl "lifting line theory" if you want to know)

I quit this discussion, I think the "longer path gives higher speed, and
thus lower pressure" theory really sucks.
If you do not need a theory, please do not use a theory. It is better to use
no theory as to use a stupid one.

Thank you for giving your opinion.

Best Regards,
Pim

Very good webpage about physical Sail/Lift Theory Pim!

The best I have seen so far on the web!

Mikko in Finland has a very good page also with airflow computer
animations.

It´s only Navier-Stokes Lift calculations that comes close to the real
physics!

Prandtl "Lifting Line Theory" is only useful for a physical non
existing "ideal/perfect fluid" created only by mathematical equations!


Jan-Olov Newborg