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2 hours ago, Spoonie said:

Last time I checked, yachts don't have mach number issues at the tip.   Or maybe they do.  I do need an excuse for a instrument wand on my masthead.

Discuss

Edit: here we go, I've found Sailor Al's gap... 

https://link.springer.com/article/10.1007/BF03186440

Haha well Terry Hutch may have found the mach number just the other day.

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Did you ‘go wrong’ when you calculated that the wind causes a pressure on the sails rather than creates lift? Foils create lift forces many times greater than the drag. 20...40 times? Also the volume

Did you just prove that you scientifically can’t sail to your rating?

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11 hours ago, JohnMB said:

Sure, but by inclination I am an experimentalist so I would want to do some wind tunnel test to verify any theory you propose. The question is will PETA get upset is we install suitable equipment to modify the topology of the cows for wind tunnel testing?

My attempts to breed spherical cows for empirical testing have been frustrating to-date. All of the candidates have required substantial post-natal trimming to even approximately comply. I have also been injured several times before realizing that the males of the species were somewhat less tractable to the procedure. I will publish preliminary results soon, initially with respect to  Von Cowman vortices, and vortex cow-shedding.

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2 hours ago, Grizz said:

My attempts to breed spherical cows for empirical testing have been frustrating to-date. All of the candidates have required substantial post-natal trimming to even approximately comply. I have also been injured several times before realizing that the males of the species were somewhat less tractable to the procedure. I will publish preliminary results soon, initially with respect to  Von Cowman vortices, and vortex cow-shedding.

Your mistake is that you're trimming them. You need to press them to shape.

Its a bit like canard a la presse, but generally you need hydraulics, the screw press will not cut it. If you do it right the gelatin will hold the cow in the correct shape.

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On 1/19/2021 at 4:33 PM, JohnMB said:

The point about changing your frame of reference is that it sometimes helps you figure out what you have missed. If you don't get the same answer in the other frame of reference then this might point you in the right direction for your error.

As several people have noted its is common practice to calculate sail forces using apparent not true wind, there is probably a good reason for this, and exploring it might give you more insight into the problem.

Transforming different references may lend insight, deriving this in spherical coordinates would be what I would assign to the perpetrator of such poor reasoning as the OP. 

If you idealize the problem to be two dimensional quasi-static, with zero pitch, yaw and roll, you should be able to figure out that you extract force at speed ==>  power from the difference in the speed of the wind and boat speed relative to water. 

No difference, no go, relative to the water.

You could be in a massive current set doing 10 kts SOG with a  following 10 kt ground wind speed; 0 True, 0 Apparent, 0 Boat speed, no steerage and your sails hanging uselessly

Whether you choose to express it in apparent wind which is probably more intuitive as you can "see" it, or true wind which is useful for selecting sails, routing and downwind steering in variable conditions should not really matter, but it's easier to keep track of and visualize what you can see. Off hand it's not clear to me that the OP is not conflating True and Ground winds. 

 

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47 minutes ago, LionessRacing said:

 Off hand it's not clear to me that the OP is not conflating True and Ground winds. 

No, he had that figured. He specified no current to avoid that complication.

His model was very simple and only tried to do a fairly simple calc. I could not see what the value was in that calc, but that's a different issue.

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1 hour ago, JohnMB said:

Your mistake is that you're trimming them. You need to press them to shape.

Its a bit like canard a la presse, but generally you need hydraulics, the screw press will not cut it. If you do it right the gelatin will hold the cow in the correct shape.

Thanks John- to be honest, I had not considered adding canards, as I am not sure they would help simplify the calculations. Kind of Dick and Burt Rutan-ish. 

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in my german book "segel theorie und praxis" printed 1964 autor C.A.Marchaj is the "trust" called VORTRIEBSKRAFT 
cross side is KRÄNGUNGSKRAFT

my father shared a buro with this autor at this time in southampton...

the little croco translated this  just with: "force to the front" and "force to heel (or hell?)"

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1 hour ago, haribo said:

in my german book "segel theorie und praxis" printed 1964 autor C.A.Marchaj is the "trust" called VORTRIEBSKRAFT 
cross side is KRÄNGUNGSKRAFT

my father shared a buro with this autor at this time in southampton...

the little croco translated this  just with: "force to the front" and "force to heel (or hell?)"

Too much kraengungskraft and to hell we all go.

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5 minutes ago, opinionated said:

52 f**c*n minutes!   Are you just joshing us?

sorry, know its been going on past its due date.  

But FFS!

There’s no test on the presentation.  It’s a complex and elegant idea, and IMHO nicely presented.  I’m sorry if it’s too long.

If I’ve caused you any distress, I apologize.

That said, when I posted it, I hoped it might be fun to listen to, but that’s it.  Not demanding that anyone look at it.  It’s ok with me that you didn’t.  You’re off the hook.  Hope you feel better?

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3 minutes ago, Amati said:

There’s no test on the presentation.  It’s a complex and elegant idea, and IMHO nicely presented.  I’m sorry if it’s too long.

If I’ve caused you any distress, I apologize.

That said, when I posted it, I hoped it might be fun to listen to, but that’s it.  Not demanding that anyone look at it.  It’s ok with me that you didn’t.  You’re off the hook.  Hope you feel better?

No issues either way.

It's cold here, with snow.   No sailing or kayaking for a while.

I learned to sail on a 30 sq m that damn near sunk on my first sail.  The feel of heel, speed, air, angle to the wind matters more to me than numbers.

Sorry to interrupt..

Carry on.

 

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2 hours ago, Amati said:

There’s no test on the presentation.  It’s a complex and elegant idea, and IMHO nicely presented.  I’m sorry if it’s too long.

If I’ve caused you any distress, I apologize.

That said, when I posted it, I hoped it might be fun to listen to, but that’s it.  Not demanding that anyone look at it.  It’s ok with me that you didn’t.  You’re off the hook.  Hope you feel better?

I didnt watch this yet but I assume this is the improved theory of optimum which accounts for wing span structueal weigjt optimisation and is decidedly not eliptical loading. Two imdependent famois aerodynamocsatsc developed at aboit samevtime but wholw world ignored it forever

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1 hour ago, fastyacht said:

I didnt watch this yet but I assume this is the improved theory of optimum which accounts for wing span structueal weigjt optimisation and is decidedly not eliptical loading. Two imdependent famois aerodynamocsatsc developed at aboit samevtime but wholw world ignored it forever

He’s put together proof of concept - it is also amazing, the chasm in Germany at the time (between the wars)  between pure science and actual building and trying- the Horton Brothers vs the scientists-

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