>>The book is a classic reference on airfoil sections and includes a substantial amount of data for different sections.

And it probably excellent in that. but it has been discovered since then that foils in proximity of surfaces and or transitions of phase will behave differently from classical Aerodynamics and their underlying idealisations of fluid. Not to mention foils that actually pierce through such surfaces

A few examples :

Why are airplane propellers different in shape than the screws on ships ?

Why have current board all a concave section near the trailing egde ? That is something that isn't part of classical Aerodynamics. Most used profile are not even NACA profiles anymore. Special profiles for boats have been developped.

What is ground effect ? And why have the russians designed a whole massive transport airplane around that phenomenon; an airplane that can carry the load of 3 or more Galaxy transport planes. Why is it intended to fly higher than its wingspan ?

What is venting and why will it never occure on an airplane wing ?

What is cavitation ?


>>Just because the data is old, doesn't mean that it isn't useful, nor that the theory behind it is flawed.

OF course but that was not the point. The point is that the data was developped under conditions that are not satisfied in real life maritime applications. The theory behind is not wrwong per se it is more that the developped theory is not applicable or insufficiently accurate for modern maritime uses. Sure a NACA foil will work just as a crocked plank will work as a rudder, but you won't win any first places with both of them nor will you find answers of weird phenomena that occure in real life sailing like venting rudders or cavitation.


>>It was (and still is) a required text in the Naval Architecture and Marine Engineering program at the University of Michigan - where I got my naval architecture degree.

It is may well be an excellent book for Aerodynamics 101, but does the material contained in the book answer any of Steves 3 questions ? That is after all the topic of this thread. I'm very sceptical about the last.


>>>The data is presented in terms of Reynolds numbers, which take into account both speed and viscosity. Doesn't matter what fluid the foil is in.


Like hell it does. Cavitation is encouterd in media in their non gas state. Airplane foils, he main interest of NACA testing do not really occupied themselfs with phenomenon like that. And as a naval architect you must know that. Reynolds numbers are cool but do not really do more than relate point the transition from viscous flow to turbulant flow and suggest how different parameters need to be chosen in model testing. They help in making data contained in graphs more accessible as well.


>>We were talking about foils in water, not foils in air.

My point exactly.

>>Besides, hang glider wings and sails are not foils. They are camber lines.

That is true. In that aspect they differ from foils. I was trying to point however that the theory of low speed foils (including wings) was developped after the book was written and that seriously different things are happening under these conditions. It is my understanding that NACA testing was mainly done from the viewpoint of establishing superior wing shapes for planes and control surfaces even blades for windmills. None of them were specically developped for use near surfaces or unders relatively large additional movements like rotations and up and down movements as encountered when sailing through waves. Rudders, keels and boards are in a pretty unsteady enviroment where the speed and direction of flow over the foil section is continiously changing with significant fluctuations. THis is completely different from steady state testing that has been performed on NACA profiles.

Sure there are many things that remain similar but again Steve has asked specific questions that point straight to contradiction in the basic steady state theory. And you, with all due respect, point him to a book that is most likely more of the classical stuff that didn't explain Steve observations in the first place.


>>You have a better reference text, Wouter?

I would start with Frank Bethwaites book on how performance sailing. I think Marchaj did some work on it as well and then I'm also at a loss. Bits and pieces are scattered over the net but I haven't encoutered a definitive book on it myself. But then again I moved to control system engineering and thus away from Nautical engineering. As a control engineer however you do encounter alot of situations where the practice doesn't do what the theory predicts it will. Than it is time to slap a control computer on the machine to put is all straight again. I must say that Frank and the Aussies as well as the russians tend to put more emphasis on real-life testing and only using theory as a start point. This has lead to some interesting developments. Sometimes people don't even know why it works but it does work nevertheless. OF course the Aussies discovered and pioneerd the prebend rigs. Do you know why they are better than the old rigs ? (of course this is not an unknown but it doubt wether it is part of 1950's curriculum)

Again, with all due respect to your person and the book itself. Those are not the things I disagree with; I have a problem with the application to this situation

Wouter