This is from an interesting article in the Nov.2003 issue of Sailing World; an interview with Juan Kouyoumdjian:
SW:What are morphing foils?
JK:When you get to a certain speed and you’re asking a foil to create lift–one side has high pressure and one side has low pressure the pressures get so low on the windward side the water might boil at 60 degrees. When you get to the cetain speed, the water simply boils and the foil cavitates and suddenly luffs the boat up or it bears away. This has been known before with propellors. But we’re now in an era where we’re seeing sailing boats hitting that wall. You can shape a foil to cavitate a little later ,but the problem is those shapes are very bad for going at lower speeds. If you start with that shape you don’t get to the high speed in the first place.Therefore, the idea of having to start with something else. By using morphing foils you can gain 4,5,6 knots extra. It’s not something that will help you to keep high averages but when you’re sailing at 25 or 30 knots, if you can have that thing that allows you to go four or five knots extra on occaision,its a good idea.
SW: So how do you make the foil change shape? Is it mechanical or material?
JK: It’s a little of both. Fortunately, nature is on our side here. The overall pressure of the water on the foil is pushing things in the direction you want.There is a combination of elastic material,like a soft rubber with a mechanical device that simply,when instructed to do so,stops resisting pressure and lets itself be deformed by the pressure around it.
SW: This is some pretty radical stuff.How sure are you it will work?
JK: There are a lot of question marks.The fact of cavitation is more than theory ,but how to make things like this work is purely theory. I’m sure the first, second and third attempts will fail and by the fourth we’ll get it right. But for sure somebody has to start doing it.
Juan Kouyoumdjian has designed a 116’ 25 ton speed machine for a client in Asia. The boat, Maiden Hong Kong uses what at first glance appears to be CBTF but according to the designer since the front foil is not connected to the rear rudder it is not CBTF. OK. I wonder if CBTF,Inc will buy that logic on the F100CBTF because the same thing is true there…hmmmm
The concept of morphing foils is interesting and could conceivably have applications on very fast models like hydrofoils that sail at speeds from zero to over 20mph using pretty much the same rudder fin thruout ; even the hydrofoils operate in a range of boatspeed from 5 to 20 +…