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Old December 3rd 08, 04:56 PM posted to alt.sailing.asa
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Default Sailing questions #1-#4

Why doesn't a keel achieve maximum efficiency with a leeway angle of 0
degrees?

What is a typical angle for maximum efficiency?

Does a catamaran have maximum efficiency at 0 degrees?

Why?



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Old December 3rd 08, 05:19 PM posted to alt.sailing.asa
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Default Sailing questions #1-#4

Charles Momsen wrote:
Why doesn't a keel achieve maximum efficiency with a leeway angle of 0
degrees?

What is a typical angle for maximum efficiency?

Does a catamaran have maximum efficiency at 0 degrees?

Why?




First, what is "Keel efficiency", and how is it measured or calculated?

Cheers
Martin
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Old December 3rd 08, 05:48 PM posted to alt.sailing.asa
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Default Sailing questions #1-#4

"Martin Baxter" wrote in message
...
troll sh*t removed
First, what is "Keel efficiency", and how is it measured or calculated?

Cheers
Martin



Like the troll would know without either looking it up or making something
up...

--
"j" ganz @@
www.sailnow.com



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Old December 3rd 08, 07:29 PM posted to alt.sailing.asa
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Default Sailing questions #1-#4

On Dec 3, 11:56*am, "Charles Momsen" wrote:
Why doesn't a keel achieve maximum efficiency with a leeway angle of 0
degrees?


Who says it doesn't?

I would say that a keel which makes ZERO leeway is highly efficient...
super-efficient.... preternaturally efficient!


What is a typical angle for maximum efficiency?


Depends on the typical aspect ratio and typical foil section.

Many boats make 3~5 degrees leeway when hard on the wind.


Does a catamaran have maximum efficiency at 0 degrees?


No of course not.

Why?


Because it's a catamaran, not an iceboat.

Fresh Breezes- Doug King
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Old December 3rd 08, 09:13 PM posted to alt.sailing.asa
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Default Sailing questions #1-#4


"Martin Baxter" wrote in message
...
Charles Momsen wrote:
Why doesn't a keel achieve maximum efficiency with a leeway angle of 0
degrees?

What is a typical angle for maximum efficiency?

Does a catamaran have maximum efficiency at 0 degrees?

Why?



First, what is "Keel efficiency", and how is it measured or calculated?


Bingo! Great job.




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Old December 3rd 08, 09:17 PM posted to alt.sailing.asa
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Default Sailing questions #1-#4


wrote in message
...
On Dec 3, 11:56 am, "Charles Momsen" wrote:
Why doesn't a keel achieve maximum efficiency with a leeway angle of 0
degrees?


Who says it doesn't?

I would say that a keel which makes ZERO leeway is highly efficient...
super-efficient.... preternaturally efficient!


~A leeway angle of zero degrees means the flow comes head on at the keel.
Since keels are symettric, the net lift is zero and the drag is a quantity
greater than zero. L/D = 0 in that case.

What is a typical angle for maximum efficiency?


Depends on the typical aspect ratio and typical foil section.

Many boats make 3~5 degrees leeway when hard on the wind.

~Correct


Does a catamaran have maximum efficiency at 0 degrees?


No of course not.

~Rethink the question with the new information about leeway angle.

Why?


Because it's a catamaran, not an iceboat.

~~Iceboats and catamarans work on very similar principles in this example.

~

Fresh Breezes- Doug King


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Old December 3rd 08, 09:19 PM posted to alt.sailing.asa
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Default Sailing questions #1-#4


"Capt. JG" wrote in message
.. .
"Martin Baxter" wrote in message
...
troll sh*t removed
First, what is "Keel efficiency", and how is it measured or calculated?

Cheers
Martin



Like the troll would know without either looking it up or making something
up...


It's a pity you can only participate in this discussion acting out of
cynicism and ignorance. Pay attention to what is discussed and you may learn
something.


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Old December 4th 08, 12:45 AM posted to alt.sailing.asa
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Default Sailing questions #1-#4

I would say that a keel which makes ZERO leeway is highly efficient...
super-efficient.... preternaturally efficient!


"Charles Momsen" wrote:
~A leeway angle of zero degrees means the flow comes head on at the keel.
Since keels are symettric, the net lift is zero and the drag is a quantity
greater than zero. L/D = 0 in that case.


Oh, you're assuming that the keel is symmetric? You didn't say that at
first. You just said zero leeway angle.

Maybe the keel you're looking at has micropores connected to a pump
that induces a pressure differential accross the foil at zero AoA,
producing lift with no leeway.

Maybe the keel you're looking at is a ballast strut and the leeway is
being eliminated by an asymmetric foil daggerboard or a toed-in
leeboard or a controllable twin foil, all of which are well proven
configurations and can produce zero leeway.

Maybe the boat is being towed to windward by a giant.

Did your physics prof introduce new conditions after the problem had
been stated and answers given? Mine didn't. But he did encourage a
wide range of correct solutions rather than dogmatically insist on a
single prosiac answer.

Fresh Breezes- Doug King
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Old December 4th 08, 01:37 AM posted to alt.sailing.asa
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Default Sailing questions #1-#4


wrote in message
...
I would say that a keel which makes ZERO leeway is highly efficient...
super-efficient.... preternaturally efficient!


"Charles Momsen" wrote:
~A leeway angle of zero degrees means the flow comes head on at the keel.
Since keels are symettric, the net lift is zero and the drag is a
quantity
greater than zero. L/D = 0 in that case.


Oh, you're assuming that the keel is symmetric? You didn't say that at
first. You just said zero leeway angle.


Also the keel is on backwards.


Maybe the keel you're looking at has micropores connected to a pump
that induces a pressure differential accross the foil at zero AoA,
producing lift with no leeway.


That's highly ineffective. The pump should pump water onto the surface of
the keel through the micropores to eliminate the boundary condition that the
water velocity=0 relative to the keel. The lift will increase by a factor of
at least 6.




Maybe the keel you're looking at is a ballast strut and the leeway is
being eliminated by an asymmetric foil daggerboard or a toed-in
leeboard or a controllable twin foil, all of which are well proven
configurations and can produce zero leeway.


They produce zero leeway for the boat. I'm talking about relative direction
between the keel and the fluid as the leeway angle.





Maybe the boat is being towed to windward by a giant.


Or by midgets.



Did your physics prof introduce new conditions after the problem had
been stated and answers given? Mine didn't.


Neither did mine, but when someone was confused or didn't understand they
did offer to explain the problem more.

But he did encourage a
wide range of correct solutions rather than dogmatically insist on a
single prosiac answer.


That's great! Did any of the wide range of solutions involve adding new
information/parameters to the question? If not, could you explain how a
science problem can have 2 correct but different answers?

Did your physics professor ever teach the "law of parsimony"?





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Old December 4th 08, 02:16 PM posted to alt.sailing.asa
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Default Sailing questions #1-#4

Maybe the keel you're looking at is a ballast strut and the leeway is
being eliminated by an asymmetric foil daggerboard or a toed-in
leeboard or a controllable twin foil, all of which are well proven
configurations and can produce zero leeway.


"Charles Momsen" wrote:
They produce zero leeway for the boat. I'm talking about relative direction
between the keel and the fluid as the leeway angle.


Same thing.

An exception would be a gybing centerboard, or a foil mounted in such
a way that it can assume an angle to the boat's centerline... but
again that would be changing the conditions after stating the problem.
Cheating!




Maybe the boat is being towed to windward by a giant.


Or by midgets.


With tiny leather harnesses!
And Argyle socks!!



Did your physics prof introduce new conditions after the problem had
been stated and answers given? Mine didn't.


Neither did mine, but when someone was confused or didn't understand they
did offer to explain the problem more.


That reminds me, why does a catamaran make zero degrees of leeway?


But he did encourage a
wide range of correct solutions rather than dogmatically insist on a
single prosiac answer.


That's great! Did any of the wide range of solutions involve adding new
information/parameters to the question? If not, could you explain how a
science problem can have 2 correct but different answers?

Did your physics professor ever teach the "law of parsimony"?


No, we were still on the "law of persimmons" at the end of the
semester. I can go back and look in my old textbook if you want.

DSK



 
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