Foil x-section
That was a very interesting article, Dave. I had to read it a couple of times to get all of the info there, not sure I have it all yet. I just want to correct one statement you made about the limitations of the IdaSailor Daggerboard design, that it is limited by the dboard well. While the gross dimensions of any dboard shoved down the well will be dictated by the inside dimensions, ie length and width, a lot of shapes that fit those two dimensions will fit down the well. The dboards that I have seen that are stock Macs are oval shaped, unlike any of the typical drawings in the article you have submitted for our edification. The IdaSailor daggerboard is not an oval, and I'll post a pic as soon as I get home of its' x-section, as my custom dboard from IdaSailor was made purposely too long, for me to mark and have cut down to the absolute maximum length that would fit in my well. I still have the trimmed off part, and I think that you will have to agree that it is closely patterned on one of the airfoils in the aforesaid article. It was interesting to read about surface smoothness as well. The HDPE plastic that Joel makes his rudders and dboards out of will take as fine a surface sand as you have patience. Having said that, I don't think any of our hulls are apt to benefit from too much Reynolds numbers concerns. But it doesn't take an engineer to appreciate that the foil that IdaSailor sells is way, way superior to the Mac oval. Only those who are really concerned about winning races to windward should replace a good dboard. Repairing a dboard is an option if you don't completely destroy it. But if you are faced with replacing and not repairing your own dboard, an IdaSailor dboard makes a lot of sense to me. The other dimension of the dboard, length, is dictated by being flush with the bottom of the boat, and so to fit on the trailer bar underneath (that assures you it will not fall down while trailering), and the upper surface of the deck flush so you can lay your stick down. On the subject of those others who worked on the designs for the Mac, there is still work being done by places like IdaSailor, and it not a set sure thing. The latest design of rudder that I have seen, the Unifoil, is shorter than I would have thought necessary to hold off a 45 degree heel without an uncontrolled round up. Also, the Unifoil rudder did not have material (much) forward of the vertical pivot line, as most of the rudder designers for the Mac have recommended. The airfoil shape of the IdaSailor rudder is what makes it good, how can that same concept not be correct for the other wing flying through the water, the daggerboard? John S
but well worth it so far. Do you have any experience to say whether or not the extra 25# was worth it? Is it a noticable difference? -cs http://groups.yahoo.com/group/bayareamacs/