Was Marchaj having us on?

AARRGH!
If we want to debate the applicability of Lift in a discussion about how sails work, have at it! but not on this thread please.
I've encouraged you to once again to divert this thread away from a discussion about Marchaj.

 

About Mark Drela's comment :
He says outside the boundary layer, rotation cannot be transmitted to the fluid.
I did not read this Nasa web page and cannot support it, but I have been learned that boundary layer is a convention defined to separate the treatment of highly viscous effect region near the wall ( high velocity gradient) with region with low viscous effect (low velocity gradient) wich is very close to inviscous potential flow. IMHO, viscosity still acts outside the boundary layer and can transmit a torque to the outside fluid .
However, I admit in the case of the rotating cylinder, the boundary layer is much thicker (and it is difficult to define his thickness , as for a Couette flow !) than on an aerofoil

 

Reply: I said nothing about a debate or a discussion. Are you putting words into my mouth?

Reply: As you wish!
I would say, in my humble opinion your past 30+ posts within the last 8 pages neither convinces nor satisfies me that Marchaj was having us on" and your question has nothing to do with a boat design.
I have broken this rule before and hope to use this great forum as it is intended.

May I suggest:
You read the forum rules before starting a new thread or continuing to post in this thread.
If you have any question about a boat design in the future you could first enter it in the search window in the upper righthand corner of the forum. Then if you don't find a existing thread that address your question there then start a new thread about your boat design question as described in the forum rules.

Thanks to all for sharing their knowledge freely.

 

Can we get back to discussing Marchaj?

 

Sailor AI,
This is a Boat Design forum not a conspiracy theory forum. If you want to discuss conspiracy you should go to a conspiracy theory forum.

Forum Rules
Keep threads & posts on topic.
1a.) New threads must be on topic based on the forum title. A thread in the Boat Design forum must be about boat design.

 

I see that there is a separate sub-forum called "Boat Design" which should probably concentrate on boat design.
This sub-forum is titled "Hydrodynamics and Aerodynamics". Marchaj's book is titled: "Aero-hydrodynamics of Sailing". That seems like a pretty close match to me.
I really am interested in what the sailing world currently thinks about his book.
I'm not sure why you're so hung up on the meta data.

 

Plus one for Howland

 

Having opened this particular can of worms,wouldn't it be best to rigorously debate it to a logical conclusion?That would mean we won't have to re-visit it in the future.

 

While we're at it, we could also have a rigorous debate about whether the Earth is flat, or whether we live inside a hollow shell. There would be no logical conclusion, no convincing the true-believers. Feeding the trolls is never a good strategy.

 

Sealioning - Wikipedia https://en.wikipedia.org/wiki/Sealioning

Cheers,

Earl

 

Sailor Al may be a troll, because he ignores many posts and points that provide opposing views to his own.

For example, in the thread where he attacked the use of the concepts of lift and drag, IIRC, he ignored the fact that some of us DO find it useful to break down the different forces. He also ignored the fact that in some sailing craft you CAN feel drag, and in some sailing craft you DO use vertical lift from the rig, and that in some sailing craft heeling forces are NOT always harmful.

When someone infers that they are seeking a truth but refuses to deal with contrary evidence it appears that they may be just trolling.

 

Marchaj used "circulation" among other concepts to explain aerodynamic force. Circulation Theory, developed by Kelvin in 1869 applies to barotropic fluids. Liquids are barotropic, gases are not barotropic. Air is a gas. Circulation Theory does not apply to air and is not relevant to the investigation of the aerodynamic force on a sail. See Aerodynamic force on a sail to see how the aerodynamic force on a sail is entirely due to the compressibility of air.

 

Hmmm Sailor Al,
At maximum pressures only around 5 kg/m2, compression would be ... err not so much.

Arvil Gentry's careful explanation of how a conventional sloop operates might remain 'best available'; 50 years after it was written.

 

I'm not sure where you sourced that number, but do the math. Over a 100 Sq metre sail, that's 500Kg or ~5,000 Newtons of force. Sounds like quite a lot to me!

It's madness! He's using a corrupted version of Kelvin's Circulation theory of incompressible fluids!