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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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On 1/20/2021 at 11:27 AM, El Borracho said:

You began the thread with units of force. Now, above, you wrote energy. I would probably work in power, though.

I know why TWS is used in polars and the like. But AWS seems better suited for this calculation.

Your idea of dragging a hull thru the water with a spring scale to establish a driving force is deeply flawed.

An aside: The blades of a wind turbine are very slender compared to the volume swept yet they extract energy from the entire swept disc. Even if transformed to the helical path vs. axial. Somehow this notion applies to your effort.

Despite my quibbles with your suggestion that my boat towing proposal is deeply flawed (I got it from this video at around 6:00) using a J32, your suggestions about using power and wind turbines has been most helpful.image.thumb.png.43ffc21ce85815823f322e194c2ad811.png

 

With my hull drag of 2,000 Newtons I need around 7 Kw thrust to propel the boat at at 7 Kts (3.5 m/s).

The formula generally used to determine power for wind turbines, P = 1/2 ρΑV^3 includes the A element of "swept area" which I am having problems with applying to a yacht.

When I set A to the sail area presented to the wind, I get a power result of around 9 Kw (see below). That in itself is a wild overstatement, since that would be the theoretical power from reducing the windspeed from TWS to zero, and that obviously doesn't happen. There's Betz Limit which sets a 'power coefficient' of 0.59 which would yield an available power of around 5.4 Kw to then be used in providing thrust, overcoming skin resistance of the sail, leeway and turbulence, so we're still way off.

image.png.20d0af16a9a9d71e72592c5ea442ca68.png

So my current challenge is to either find an alternative algorithm or establish a value for the swept area, A, of my sail to get a sensible answer.

 

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Do the sails consume only some small fraction of the wind energy that intersects their projected surface area? Probably. Do the sails extract energy from a much larger area, or volume, than your simplistic projected area region? Probably.

Consider lee bow effects (theft of energy) at considerable distances relative to sail plan dimensions.

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12852.jpg?u=1611310984

einstein setting sail on his wooden boat between 1929 - ´33, schwielowsee near potsdam/D

Einstein was no racer. He may not even have been much of a sailor. He never made any great contribution to the sport. But he showed that dinghy sailing could be a source of never-ending delight to the most brilliant of humans. He also showed that even the greatest of scientific minds cannot always understand the theory of sailing.

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if you try to calculate the force of a sail/wing you must calculate the change of direktion and speed of the air also a bit more fare away of the projekted part of air

you need the sum of all,  it is not only the orange part of air involved! mayby the significantly larger amount of air between the two yellow areas could affect it, an areal much bigger than the area of the sail and much-much bigger than your projekted part , all this air change speed and direktion behind the wing/sail

pysicofsail.png.dbdab04822e28f23972781cee20ad413.png
by the way tuching the sail is in theoreticly only one loonly layer from the air (the red one) witch is in this picture far outside of the projekted orange areal

only this minimal part of the air stopp to nearly zerro-speed and move very slow along the sail on borth sides

 

 the normal way is: mesure the total sum of all involved forces in a wind cannel and "per definition" calculate it back of the sail-area

and this definition is the reason why the lift can be greater than 1!

 your first thought was right, the force can never be greater than 100% of the involved air, but if by definition you calculate down to a surface that is smaller(!) than the involved air comes out just > 1 and on ours boats the CL can be  between 0.9 and up to 1.7

You could also count on the projection area you set up, but we do not do that because this would not make the calculation better, but only considerably more complicated, you would have to re-determine the projected area if you changed the flow angle, so all agreed to set up the simple sailing area, about 100 years ago.

the further calculation path of CL and CD of the sail in the longitudinal and transverse direction to the ship is quite normal vector calculation

haribo

p.s. english is not my mother language

 

picture is from

www.av8n.com/irro/profilo1a_e.html

 

 

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6 hours ago, El Borracho said:

Do the sails consume only some small fraction of the wind energy that intersects their projected surface area? Probably. Do the sails extract energy from a much larger area, or volume, than your simplistic projected area region? Probably.

Consider lee bow effects (theft of energy) at considerable distances relative to sail plan dimensions.

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.726.9922&rep=rep1&type=pdf

old school (sic) for the mathematically inclined 

https://ntrs.nasa.gov/api/citations/19930091216/downloads/19930091216.pdf

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9 hours ago, Frogman56 said:

Al,

The longer F40 hull will have less drag than the J32 at 7 knots...

Quite possibly, certainly it will have a higher Hull Speed but without experimental (or solid theoretical) data I'm sticking with my 2,000 as a first approximation. 

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7 hours ago, haribo said:

if you try to calculate the force of a sail/wing you must calculate the change of direktion and speed of the air also a bit more fare away of the projekted part of air

Thanks for that, but you are offering a non numerical discussion about aircraft which derive all their power from their engines, so I don't think it is relevant.

I'm looking for a mathematical solution for sailing boats which derive all their power from the wind.

 

 

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2 minutes ago, Sailor Al. said:

 sailing boats which derive all their power from the wind.

They don't, you know. The power comes from reducing the difference in vectors between wind and water, and there is lift and drag in the water as well as the wind. After the boat passes the water is just as disturbed as the air. At this point frames of reference start confusing people... 

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10 hours ago, El Borracho said:

Do the sails consume only some small fraction of the wind energy that intersects their projected surface area? Probably.

Wind turbines only extract around 20%, so I'm pretty sure a low-tech sail will extract considerably less.

 

10 hours ago, El Borracho said:

Do the sails extract energy from a much larger area, or volume, than your simplistic projected area region? Probably.

But how much? and why?

10 hours ago, El Borracho said:

Consider lee bow effects (theft of energy) at considerable distances relative to sail plan dimensions.

The answer to that question is my Holy Grail!

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16 minutes ago, JimC said:

They don't, you know. The power comes from reducing the difference in vectors between wind and water, and there is lift and drag in the water as well as the wind. After the boat passes the water is just as disturbed as the air. At this point frames of reference start confusing people... 

There is no energy in vectors, and, in the Earth frame of reference, in which the boat is operating, there's no energy in the water, so I'm pretty sure we can be confident that the only source of power driving a sailboat through the water against the drag of the hull in the water, is the energy of the wind.

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4 hours ago, Amati said:

Great reading those old papers, but like I said, aircraft derive their power from their engines, and I'm searching for a quantification of the power (from the wind) that drives a sailboat.

The mechanism by which the sails extract the power from the wind to provide VMG thrust is the subject of aerodynamics, which is a whole different kettle of fish.

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3 minutes ago, Sailor Al. said:

Great reading those old papers, but like I said, aircraft derive their power from their engines, and I'm searching for a quantification of the power (from the wind) that drives a sailboat.

The mechanism by which the sails extract the power from the wind to provide VMG thrust is the subject of aerodynamics, which is a whole different kettle of fish.

I don't think you'll get to where you want to go w/o aerodynamics. 

You've already established that the flow field has more KE than required to overcome your assumed hull drag.

You've come up with a theoretical maximum for the energy that can be extracted from the flow field (though I think you're a bit sloppy w/ your reference frames there)

After that, you're looking at the efficiency of the sail plan at extracting that available energy. 

That puts you smack into aerodynamics.

Not sure you can get to where you want to be w/ the tools you're allowing yourself.

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44 minutes ago, Sailor Al. said:

Thanks for that, but you are offering a non numerical discussion about aircraft which derive all their power from their engines, so I don't think it is relevant.

I'm looking for a mathematical solution for sailing boats which derive all their power from the wind.

 

 

That diagram looks exactly the same for gliders/sailplanes which have no engines. I don't think the "source" of the apparent wind matters to the wing (or sail), whether it is an engine moving a powered aircraft through the air, gravity moving a glider through the air, or the water resisting a sailboat moving when the wind blows over its wing.

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2 minutes ago, Mark Morwood said:

That diagram looks exactly the same for gliders/sailplanes which have no engines. I don't think the "source" of the apparent wind matters to the wing (or sail), whether it is an engine moving a powered aircraft through the air, gravity moving a glider through the air, or the water resisting a sailboat moving when the wind blows over its wing.

Gliding 101: gliders get their energy to fly level or climb from the upwards flow of air from thermals or mountain lift. Without that, they descend to earth, using the conversion of the potential energy of height to kinetic energy of motion (producing lift) to slow their descent.

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1 minute ago, Sailor Al. said:

Gliding 101: gliders get their energy to fly level or climb from the upwards flow of air from thermals or mountain lift. Without that, they descend to earth, using the conversion of the potential energy of height to kinetic energy of motion (producing lift) to slow their descent.

I understand how gliders work. I'm off to fly one today. It's a long time since I've done any formal physics, but it seems to me you seem to be misunderstanding/ignoring the importance of frames of reference. The glider wing has no idea if it is in rising air or sinking air, though the pilot is very aware. The wing continues to provide lift from the flow of air over the wing regardless. Finding rising air is important if you want to extend your time in the air, but in any case all of the time you are flying with positive G's the wing is slowly descending through the surrounding air. It is all about the apparent wind in sailing terms.

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50 minutes ago, Sailor Al. said:

I'm looking for a mathematical solution for sailing boats which derive all their power from the wind.

You have shown that some of your assumptions are wrong, there have been several suggestions as to which..

Things you might want to consider:

-Why is the drag coefficient of a rectangular plate normal to the air flow greater than 1.

-When calculating the drag force on a rectangular plate normal to the flow, if the plate is moving relative to the reference frame what velocity would you use to calculate the drag force? (air velocity relative to the frame, or air velocity relative to the plate, or some other velocity)

Its not at all clear to me why you want to model a sailboat in this way. Usually I like models which give me insight into the problem, and help me improve the system I'm considering, its not clear how this model will do that. 

If you are interested in the energy flow, you are changing the velocities of the air and the water,  but depending on the frame you work in you could be transferring energy from the air to the water or from the water to the air, either way you will be reducing the relative velocities of the two fluids.

Personally I think way you are trying to calculate this you will end up throwing the baby out with the bathwater, as I think your simplifying assumptions will eliminate any useful insights, but I could be wrong.

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9 minutes ago, stinky said:

You've already established that the flow field has more KE than required to overcome your assumed hull drag

No, I haven't, and that's my challenge! At this stage I have just shown that I am unable to use the wind turbine formula to derive anything like enough power for the job.

 Aerodynamics derives lift and drag from thrust.

We need energy to provide the thrust and the only source of energy is the wind. Conservation of energy is fundamental.

Aerodynamics can't generate energy.

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14 minutes ago, Mark Morwood said:

I understand how gliders work. I'm off to fly one today. It's a long time since I've done any formal physics, but it seems to me you seem to be misunderstanding/ignoring the importance of frames of reference. The glider wing has no idea if it is in rising air or sinking air, though the pilot is very aware. The wing continues to provide lift from the flow of air over the wing regardless. Finding rising air is important if you want to extend your time in the air, but in any case all of the time you are flying with positive G's the wing is slowly descending through the surrounding air. It is all about the apparent wind in sailing terms.

As a fellow glider pilot, but with some recent experience in formal physics, can I suggest you talk to your CFO. A glider needs the energy of rising air to maintain airspeed in horizontal or climbing flight.  

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1 hour ago, Sailor Al. said:

Great reading those old papers, but like I said, aircraft derive their power from their engines, and I'm searching for a quantification of the power (from the wind) that drives a sailboat.

The mechanism by which the sails extract the power from the wind to provide VMG thrust is the subject of aerodynamics, which is a whole different kettle of fish.

2009 is old?  Anyway, I was responding to Boracho.  You have picked an Everest to climb, and if you get there, I hope you write a text.  Please include the quantum mechanics of sailing?  Please?

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1 hour ago, Sailor Al. said:

No, I haven't, and that's my challenge! At this stage I have just shown that I am unable to use the wind turbine formula to derive anything like enough power for the job.

 Aerodynamics derives lift and drag from thrust.

We need energy to provide the thrust and the only source of energy is the wind. Conservation of energy is fundamental.

Aerodynamics can't generate energy.

confused, you're getting ~9000 watts available from the flow, and assuming ~2000 watts lost to hull drag.

Am I misreading what you've written?

9000>2000

9000*.59>2000

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9 minutes ago, stinky said:

Am I misreading what you've written?

At last, someone is looking at the detail, thanks.

What worries me is that 9000*.59 = 5,400 and that would indicate an efficiency of 2/5.4 = 34% conversion of available wind energy to thrust, which, if it's true, seems to me to be an amazingly high efficiency for a sail!.

Maybe it's right and I'm worrying unnecessarily, but I'd like the number to be peer reviewed before I publish a paper!

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2 minutes ago, Sailor Al. said:

At last, someone is looking at the detail, thanks.

What worries me is that 9000*.59 = 5,400 and that would indicate an efficiency of 2/5.4 = 34% conversion of available wind energy to thrust, which, if it's true, seems to me to be an amazingly high efficiency for a sail!.

Maybe it's right and I'm worrying unnecessarily, but I'd like the number to be peer reviewed before I publish a paper!

I think it becomes more realistic if you fix your ref frames.

I think you need apparent wind, not true.

Either that, or flip the sign on your drag #.

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3 hours ago, Sailor Al. said:

Thanks for that, but you are offering a non numerical discussion about aircraft which derive all their power from their engines, so I don't think it is relevant.

I'm looking for a mathematical solution for sailing boats which derive all their power from the wind.

Nope. Exactly relevant. The names of the axes and vectors change, that is all. There are some very knowledgeable sailors here trying to help. You will need calculus (in 3D) to model the infinite (asymptotic) energy field that you seek.  Move your VisiCalc work over to Mathematica...

The lee bow effect, which you say is your goal, is infinite too. The decision to tack away can only be made by an experienced racer based on tactics, strategy, feel, risk assessment, etc... fortunately no mathematical modeling needed.

11 hours ago, haribo said:

 

pysicofsail.png.dbdab04822e28f23972781cee20ad413.png
 

Fabulous illustration of the flow and displacements (energy). Thank you. I love your rendition of english. I wish my foreign language skills were as good as yours.

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7 hours ago, Amati said:

Heh...oh yeah...I forgot about the circulation flow. One of the things that attracted me to re-enter sailing after a long career in engineering was the lack of need to understand why it works.

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1 hour ago, El Borracho said:

Heh...oh yeah...I forgot about the circulation flow. One of the things that attracted me to re-enter sailing after a long career in engineering was the lack of need to understand why it works.

It’s like music that way- the left brain can inform the right brain for intuitive understanding, if that’s what you’re in to.  Both work.  It’s magic.  I like how each side of the brain helps the other build.  Things happen from moment to moment.

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Al, as a (once, long time ago) physicist I think I understand the question you are asking. As you say, conservation of energy is fundamental (to everything!)

If a partially submerged object (such as a boat, forget about the sails for now) is presented to the wind, it will either stay where it is if its frictional forces are greater than the wind forces, or be pushed backwards by the wind if not.

The sailing complication is that it is a dynamic not static situation. This maybe explains the wind turbine situation; as a blade moves it is presented to "new" wind so can extract energy from the entire circular area. Similarly as a yacht moves it sees new wind which brings in a bunch of aerodynamic complications.....

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17 minutes ago, Fleetwood said:

Al, as a (once, long time ago) physicist I think I understand the question you are asking. As you say, conservation of energy is fundamental (to everything!)

If a partially submerged object (such as a boat, forget about the sails for now) is presented to the wind, it will either stay where it is if its frictional forces are greater than the wind forces, or be pushed backwards by the wind if not.

The sailing complication is that it is a dynamic not static situation. This maybe explains the wind turbine situation; as a blade moves it is presented to "new" wind so can extract energy from the entire circular area. Similarly as a yacht moves it sees new wind which brings in a bunch of aerodynamic complications.....

Physicists are not up to the task of hydrodynamics. Feynman said so :-P

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25 minutes ago, fastyacht said:

Physicists are not up to the task of hydrodynamics. Feynman said so :-P

Hydrodynamics is physics, what else would it be? I think Feynman was talking about quantum mechanics - "no-one understands quantum mechanics", to which he added "shut up and calculate".

As Rutherford said, "all science is either physics, or stamp collecting".....

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1 hour ago, Fleetwood said:

Hydrodynamics is physics, what else would it be? I think Feynman was talking about quantum mechanics - "no-one understands quantum mechanics", to which he added "shut up and calculate".

As Rutherford said, "all science is either physics, or stamp collecting".....

Nope. He said something like, hydrodynamics is to damned hard" or something.

The corollary is, "Naval architects are not up to the task of quantum mechanics. Fastyacht said so":)

AS for Rutherford, well, he was one of "those" presidents. Haha.

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18 hours ago, Sailor Al. said:

Thanks for that, but you are offering a non numerical discussion about aircraft which derive all their power from their engines, so I don't think it is relevant.

I'm looking for a mathematical solution for sailing boats which derive all their power from the wind.

 

 

my argument related to the selection of the reference surface for the forces at which you propose projected sail surface and usually the entire sail surface is used.
nothing related to aircraft or engines or anything else but if you don't want to remember sailing ships with profiles (americas cup 2013) then I like to change the profile in the picture against a sail behind a mast...

assume it would be a cross section of a sail in a wind tunnel.

haribo

 

pysicofsail2.png

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22 hours ago, stinky said:

confused, you're getting ~9000 watts available from the flow, and assuming ~2000 watts lost to hull drag.

Am I misreading what you've written?

9000>2000

9000*.59>2000

After a day's racing and another good night's sleep, I have returned to the problem and found a fly in the ointment.

Here's the problem, the hull drag is 2,000 Newtons of force, so the power required to propel the boat at 7 kts (3.5 m/sec) is 3.5 (m/sec)* 2,000(Newtons) =  7,000 watts. 

The 9,000 watts of wind power would only be extracted if the wind speed was reduced to zero, and we know that doesn't happen, hence the Betz limit of .59 , giving a maximum power available of 5,300 watts, and that's well short of the 7,000 watts required.

So, back to the drawing board.

 

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On 1/23/2021 at 7:21 AM, Sailor Al. said:

As a fellow glider pilot, but with some recent experience in formal physics, can I suggest you talk to your CFO. A glider needs the energy of rising air to maintain airspeed in horizontal or climbing flight.  

You completely missed my point as you appear to have when others above have suggested things you didn't want to hear.

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40 minutes ago, Mark Morwood said:

You completely missed my point as you appear to have when others above have suggested things you didn't want to hear.

My question is how to quantify the power that's available from the wind to propel the boat against the drag of the water.

The offerings I may appear to "miss"  (by not replying) fall into three categories:

  1. Those that relate to the mechanism of extracting the power of the wind to power the boat through the water, such as aerofoils and aerodynamics. That is obviously the whole point of sail design and trimming, but is the answer to a different question
  2. Those that relate to systems that have an external source of power, such as a plane's engine. Introducing an external source of power only confuses the issue. 
  3. Those relating to topics away from my problem area (mistresses, use of jibs etc, etc)

I replied to your post as you appeared to have overlooked the fact that gliders rely entirely on the power of the wind in the rising air to provide the lift to overcome its weight and the thrust to propel it through the drag of the air.  Any further discussion relating to gliders wings falls into my category 1. above. 

So it may appear that I have "totally missed" your point, but it has in fact been noted as not being relevant to my problem.

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On 1/23/2021 at 4:03 AM, Sailor Al. said:

Thanks for that, but you are offering a non numerical discussion about aircraft which derive all their power from their engines, so I don't think it is relevant.

I'm looking for a mathematical solution for sailing boats which derive all their power from the wind.

Nope. Exactly relevant. The names of the axes and vectors change, that is all. There are some very knowledgeable sailors here trying to help. You will need calculus (in 3D) to model the infinite (asymptotic) energy field that you seek.  Move your VisiCalc work over to Mathematica...

The lee bow effect, which you say is your goal, is infinite too. The decision to tack away can only be made by an experienced racer based on tactics, strategy, feel, risk assessment, etc... fortunately no mathematical modeling needed.

On 1/22/2021 at 8:08 PM, haribo said:

 

pysicofsail.png.dbdab04822e28f23972781cee20ad413.png
 

Fabulous illustration of the flow and displacements (energy). Thank you. I love your rendition of english. I wish my foreign language skills were as good as yours.

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1 minute ago, El Borracho said:

Nope. Exactly relevant.

No, sorry, not relevant as it falls into my category 1 (above) as it relates to the mechanism of extracting wind power, not the quantification of the wind power.

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8 minutes ago, Sailor Al. said:

No, sorry, not relevant as it falls into my category 1 (above) as it relates to the mechanism of extracting wind power, not the quantification of the wind power.

Foolish. Ridiculous rules you have set. The global quantity of power available in the wind is a big number, right? So how much you can capture is based on the mechanism one builds....

You might explore how energy fields work. Electromagnetic, even. They do not follow your over-simplified musings. And probably beyond spreadsheet calculation capabilities.

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1 hour ago, El Borracho said:

Foolish. Ridiculous rules you have set. The global quantity of power available in the wind is a big number, right? So how much you can capture is based on the mechanism one builds....

You might explore how energy fields work. Electromagnetic, even. They do not follow your over-simplified musings. And probably beyond spreadsheet calculation capabilities.

Spreadsheets are for feeble minds. Databases are for dudes. :-P

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On 1/21/2021 at 7:57 PM, Snaggletooth said:

I thouhte teh Bobbe Greenhole wille kille you foire a plane quiote.............or wespey in a nihtey thouht to be ghoste mitte quallify to.............                 :)

 

Wespey ina nighty.... There's some nightmare fuel. 

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On 1/22/2021 at 1:12 PM, JohnMB said:

I think your simplifying assumptions will eliminate any useful insights, but I could be wrong.

Sailor Al:  Consider a cow, standing in a field, in a 7 knot (3.5 m/s) wind blowing into the cow's face.

Now assume the cow is a perfect sphere....

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19 minutes ago, Zonker said:

Sailor Al:  Consider a cow, standing in a field, in a 7 knot (3.5 m/s) wind blowing into the cow's face.

Now assume the cow is a perfect sphere....

You mean something like this?   But you didn't specify Holstein or Black Angus.

th-1.jpeg

th-2.jpeg

 

What if the cow farts? 

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4 minutes ago, Zonker said:

Do you get Von Karman vortexes from a sphere as well as a cylinder?

Research will begin tomorrow.  There has to be some reason for dimples on golf balls and the knuckle ball's behavior.  

(Vortices?)

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OK guys, game over.

The answer is 53%

To those of you who insisted I use apparent wind speed and angle, thank you, sorry it took so long for the penny to drop.

In the steady state, the boat experiences the  dynamic pressure from the apparent wind, not the true wind.

image.thumb.png.1c6f3ef7b36312c0601193e544618693.png

Here's the working sheet 

Thanks and good night.

 

image.png

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28 minutes ago, Sailor Al. said:

OK guys, game over.

The answer is 53%

To those of you who insisted I use apparent wind speed and angle, thank you, sorry it took so long for the penny to drop.

In the steady state, the boat experiences the  dynamic pressure from the apparent wind, not the true wind.

image.thumb.png.1c6f3ef7b36312c0601193e544618693.png

Here's the working sheet 

Thanks and good night.

 

image.png

I hope you didn't hurt your brain.  But you did waste your time.

That is about the least useful set of data for an actual sailor that I can imagine.  Did you have fun!

 

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1 minute ago, Left Shift said:

I hope you didn't hurt your brain.  But you did waste your time.

That is about the least useful set of data for an actual sailor that I can imagine.  Did you have fun!

 

Sounds like sour grapes to me.

And yes, thanks, I enjoyed the exercise and feel that I have a better understanding of how the AC75's achieve 40kts from a 15 kt breeze.

Whether they're upwind or downwind, they have an AWS of heaps, an AWA of bugger all, and extract heaps of power to overcome the seriously low drag on the foils.

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11 minutes ago, Sailor Al. said:

Sounds like sour grapes to me.

And yes, thanks, I enjoyed the exercise and feel that I have a better understanding of how the AC75's achieve 40kts from a 15 kt breeze.

Whether they're upwind or downwind, they have an AWS of heaps, an AWA of bugger all, and extract heaps of power to overcome the seriously low drag on the foils.

Did you just wake up yesterday? Are you Rip Van Fucking Winkle? There's this thing called an iceboat. Been around almost as long as the God's have been playing ninepins (and right under their noses literally). Look them up.

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31 minutes ago, shaggybaxter said:

Why didn't you model the effect of the keel? 

Ah, yes, keel lift, that's delving into hydrodynamics.

The keel is moving through the water at Boat Speed with an AoA of the angle of the leeway angle, typically around 5°.

I know it produces lift, effectively increasing the righting moment, but that comes at the expense of drag.

I don't think it provides thrust, quite the opposite, it increases the drag. Do you have any thoughts?


 

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20 minutes ago, Sailor Al. said:

I don't think it provides thrust, quite the opposite, it increases the drag. Do you have any thoughts?

And off we go! Of course the underwater foils cause thrust. Delete them (keel rudder and hull form) from your mathematical model and report back on the boat motion vector.

A primitive calculation of the same form as you derived above with the labels switched around will show that the energy for moving the boat and rig thru the atmosphere comes completely from water acting upon the underbody parts.

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the second last line in your sheet: power  [watts]  =  force*AWS  

2197 * 9,2 =20120 ??? (you use mayby TWS?)

 

 

@El Borracho   is the water and air behind a boat  warmer(hotter)?

 

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Calculating available power using TWS and projected area of a sail will never work, unless you can account for the energy absorbed by the surrounding air. 

IOW, it is not possible to only extract energy from the projected sail area.

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6 minutes ago, haribo said:

the second last line in your sheet: power  [watts]  =  force*AWS  

2197 * 9,2 =20120 ??? (you use mayby TWS?)

 

Corrected, many thanks. I thought 53% was too high, the new result of 36% is much more realistic.

image.thumb.png.bc1a5418af19e8524fffa500baf0a4fa.png

 

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6 minutes ago, Thread Killer said:

Calculating available power using TWS and projected area of a sail will never work, unless you can account for the energy absorbed by the surrounding air. 

IOW, it is not possible to only extra energy from the projected area.

but it is a plausibility assessment in the sense of caloric

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15 minutes ago, haribo said:

@El Borracho   is the water and air behind a boat  warmer(hotter)?

That notion did occur to me, however just for a moment.... the wife called me for a delicious lunch of fried tofu with thai chili sauce over rice. Now I’m watching my morning concrete pour set.

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5 minutes ago, El Borracho said:

Now I’m watching my morning concrete pour set.

how's that rate on a paint drying scale ?

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6 minutes ago, El Borracho said:

fried tofu with thai chili sauce over rice

going out on a limb here and expressing gratitude that I married a Thai ........................

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2 minutes ago, Mid said:

how's that rate on a paint drying scale ?

No interruptions to pick flies out of the paint. And the dogs are too exhausted to make footprints from their long night of destroying the sand pile. Pretty relaxing, actually.

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more realistically as that your F40 sail slow down a 42m2 cross section of the wind  from 9.2 to ~ possible 7.9 m/sec

is the calculation that would be a cross section of air from, perhaps, 300m2 slow down from 9.2 to 9.1 m/s (same energie difference)

I wanted to show nothing else in #106
(42m2 is only the orange part of the picture)

and I had also assumed that the force deflection would also be important...
 because it considerable forces and energieen, but as you write that another could be also asks

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By using AWA alone to project your firces, you are making the implicit assumption that your sails are in a plane that is vertical and along the longitudinal axis of the boat.

Any good sailor knows that such a boat wouldn't sail forward!

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Did you notice the cow velocity - the flow is hypersonic. Which would cook the cow. Surely there are easier ways to bbq a cow that making it go that fast?

 

Also the cow lacks a keel, thus it would suffer massive loss of stability as it bears off. 

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1 hour ago, Panoramix said:

By using AWA alone to project your firces, you are making the implicit assumption that your sails are in a plane that is vertical and along the longitudinal axis of the boat.

Any good sailor knows that such a boat wouldn't sail forward!

in usual aero/hydrodynamic force calculation is his example realistic:
beta~15 °; CL=1.57; CD=0.31
... lift = A * roh / 2 * CL * v ² =  98 * 1.22/2 * 1.57 * 9.2² = 8000 [N] =8 [KN]  
(yes we calculate it per definition of LIFT and DRAG with the whole sailing area A=98m² not with the projected !!!)
likewise the drag ~ 1.6 [KN]

the usual geometric vector calculation:
= = = > force in line of the boat = 2 [KN]
force across the boat ~ 7.9 [KN]
everything is in expected sizes

but in his therms with energy? what is the energy of lift; drag? what energy we need do heal a F40?

how much energy is needed to divert the wind forces?
I find this energy approach unusual but also interesting

haribo

pysicofsail3.png

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@hariboEnergy approach is interesting, but also results in serious headache..

It is all about which control volume you choose. Large enough control volume and the answer is zero (when consider typical boundary conditions). It really about picking right control volume for the losses you are interested in.

For @Sailor Al.suggest to think why there is field continuum mechanics.

Thanks anyway, this helped me figure out approach to put another somewhat related discussion in right context.

 

 

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12 hours ago, Sailor Al. said:

I replied to your post as you appeared to have overlooked the fact that gliders rely entirely on the power of the wind in the rising air to provide the lift to overcome its weight and the thrust to propel it through the drag of the air.

That cannot be right.

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8 hours ago, Sailor Al. said:

Ah, yes, keel lift, that's delving into hydrodynamics.

The keel is moving through the water at Boat Speed with an AoA of the angle of the leeway angle, typically around 5°.

I know it produces lift, effectively increasing the righting moment, but that comes at the expense of drag.

I don't think it provides thrust, quite the opposite, it increases the drag. Do you have any thoughts?


 

So take them off and report back about your experience with DDFTTW

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15 hours ago, Left Shift said:

You mean something like this?   But you didn't specify Holstein or Black Angus.

th-1.jpeg

th-2.jpeg

 

What if the cow farts? 

DDWFTTW?

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7 hours ago, El Borracho said:

That cannot be right.

One feature of the scientific method is that a theory remains current until either a) disproved or b) replaced by a better one. Just saying it's not right doesn't really fall into that domain.

Are you proposing a) or b)?

 

 

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