Revolutionary Centerboard!!

as the extra mass would be stored in the hull it would'nt make any difference to righting moment.the board in the water would still have the same mass and the same lever so the same righting moment. it would make a difference to the pitching moment of the yacht as their would be more mass lower down in the boat thus lowering the centre of gravity of the boat.but only slightly.

on the subject of building foils you have a multitude of choice depending on the class rules of the boat. personally i would use very high density foam 200kg/m3 plus and uni directional carbon

as hyrodynamic as possible I think, ie good airfoil section. 

Flat is not necessarily good because you have to transition from leading edge to flat surface to trailing edge again and sudden changes in curve cause the water to accelerate quickly, creating displacement force.

I guess, but don't know for sure, that a really thin board will be good - if you can make it stiff enough not to twist off.

Upon which .... has anyone tried making their own foils?  Out of what?

The gospel according to Bethwaite reckons the extra lift will never make up for the extra drag.

Water being so stiff, you hardly need any angle of attack to get lift, and sufficent angle of attack comes from the boat sailing along very slightly diagonally when sailing up wind.

Having said which, I sailed with an aged GP14 sailor once who insisted on heeling the boat to leward when sailing up wind, even in a blow, as the curve in the hull gave him extra pointing - and out point everyone else we did!

So maybe if you make the asymetry subtle enough....

i know you said clever people only but im going to say something anyway. how would you store the spare board? it would have to be a centreboard boat i thjink. it might be worth it a class with a heavier weight so you get more righting moment from the board. i dont see why it wldnt work if you got a fairly decent shape but that might need alot of trail and error to sort out.

go for it mate!