"Simple Simon" wrote in message
...


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.

Nonsense!

There is an absolutely negligible difference in length between the windward
and leeward paths.

The wind pushes the windward side of the sail. The keel stops the boat from
moving sidways, and the pressure is relieved by the forward movement of the
boat.



Try pushing a knife through butter to see what I mean.


If your theory were correct, then a boat would go *faster* upwind.



Regards


Donal
--


"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
--

How a sail owrks: Big stick...big piece of cloth....wind.....wind pushes boat...what else do you need to know/

--
katysails
s/v Chanteuse
Kirie Elite 32
Ad eundum quo nemo ante iit.
http://katysails.tripod.com

"Women and cats will do as they please, and men and dogs should relax
and get used to the idea." - Robert A. Heinlein

"katysails" wrote ...
How a sail owrks: Big stick...big piece of cloth....wind.....wind pushes
boat...what else do you need to know?

how full the ice box is?

Scotty

how full the ice box is?

Right now it's full of kimchee and tofu....gonna get those kids to eat nasty old peanut butter if it kills me....

--
katysails
s/v Chanteuse
Kirie Elite 32
Ad eundum quo nemo ante iit.
http://katysails.tripod.com

"Women and cats will do as they please, and men and dogs should relax
and get used to the idea." - Robert A. Heinlein

Bwahahahahaha!

RB

Neal,

Be very careful with your statement on this discussion. You are about to
be swallowed by Newton's first three laws.
I can feel the smiling, sneering faces.. They know "Bernoulli' is
incomplete about sail action. Newton's 1st,2nd,and 3rd Laws are true and
more complete BUT
either is Newton's Laws. They don't cover the Cosanda (probably wrong
spelling) or the apparent circulation forces.

I'm still in a muddle about this since the first time thru it. Our
Newtonians are using flight theories, which are based on vertical
forces. They use terms like ground effects, updrafts and downdrafts
which haven't been truly converted to
horizontal. They are probably right but also incomplete.

Let it go Neal, my friend, Bernoulli will not stand up to close
examination. The Newtonian are dingking around for answers they don't
have. Drop it on them!

And; "I'LL DRINK TO THAT!"

Ole Thom
P/S Bernoulli will answer your sailing needs.

A Chord is a combination of musical tones.

A scale is a freckle on a fish

So What?

Will move in the direction of the lower pressure

Why in the hell couldn't you see that when we were talking about weather
systems?

OT

"Wally" wrote in message
...
"Donal" wrote in message news:bed29j$spv$1

There is an absolutely negligible difference in length between the
windward
and leeward paths.

I just drew a 3000mm long polyline in a CAD package and bent it into an
approximation of a section through filled sail viewed in plan. I then
offset
a new polyline from this by 1mm, simulating the thickness of the cloth.
The
lengths of the inner and outer surfaces on my model are...

Inner: 3016.6077mm
Outer: 3016.9590mm
Delta: 0.3513mm

(For reference, after manipulation, the chord is 2999.6548mm, and the
depth
of the 'belly' is 114.2920mm, 715.08mm from the leading edge.)

Doesn't seem like that could have much effect. Perhaps the Cappy's sails
are 2mm thick??



The wind pushes the windward side of the sail. The keel stops the boat
from
moving sidways, and the pressure is relieved by the forward movement of
the
boat.


Are you saying that the *only* force moving the boat forward is the push
on
the windward side of the sail? If so...

Ahhhh! What is the difference between "push" and "pull". The sail only
notices a "difference".



If your theory were correct, then a boat would go *faster* upwind.

...does it go fastest downwind?

Yes! I've done 15 kts downwind. (using a spinaker).

Me best hourly average (8.2kts) was done on a beam reach......... hmmm!
That might not be true. I've done Portsmouth entrance to St. Vaast lock in
9:45 under spinaker. WE must have had a few hours of 8.5 kts in that
trip. I suspect that we weren't writing up the log on that one. Otherwise
I'd remember it. I'll have a look tonight.


Regards


Donal
--

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?





"Thomas Stewart" wrote in message ...
Neal,

Be very careful with your statement on this discussion. You are about to
be swallowed by Newton's first three laws.
I can feel the smiling, sneering faces.. They know "Bernoulli' is
incomplete about sail action. Newton's 1st,2nd,and 3rd Laws are true and
more complete BUT
either is Newton's Laws. They don't cover the Cosanda (probably wrong
spelling) or the apparent circulation forces.

I'm still in a muddle about this since the first time thru it. Our
Newtonians are using flight theories, which are based on vertical
forces. They use terms like ground effects, updrafts and downdrafts
which haven't been truly converted to
horizontal. They are probably right but also incomplete.

Let it go Neal, my friend, Bernoulli will not stand up to close
examination. The Newtonian are dingking around for answers they don't
have. Drop it on them!

And; "I'LL DRINK TO THAT!"

Ole Thom
P/S Bernoulli will answer your sailing needs.