Also, I have been to the Idasailor (Rudder Craft) website and noticed that their rudders, which everyone really likes as they perform well and are built well, are NACA 0012 airfoil designs (the cross-section shape). Well, NACA airfoil designs have been publicly available for decades...nothing private or hidden.
So, as a good-faith effort to help out my fellow sailors and make our Mac's perform better than other boats out there
, I developed a little spreadsheet that will calculate the coordinates of a NACA 00xx symmetrical airfoil for you... For the sake of this post, width or chord is the rudder measurement from leading edge to trailing edge, thickness is just that (like how much meat is on your sammich), and length or depth will mean the top-to-bottom measurement of the rudder (as in, how far it sticks down into the water).You need the chord dimension you want to use. I found that Idasailor on their website shows their chord dimensions when you look at the rudder for your particular model boat. However, you may want to experiment with slightly wider or thinner rudders to see how it affects your performance...for example, with a good airfoil design, you might be able to get away with skinnier rudders, less drag, better performance...perhaps at the expense of slow-speed performance. (I suspect 1/2" width differences won't make an appreciable difference in whether the boat steers or not...I like to use even numbers and/or 1/2" increments, for example, so instead of 11.387562" I would use 11" or 11-1/2".)
You also need the NACA airfoil design you want. The 0012 is the one Idasailor uses, and is probably a proven one (which may be why they chose it), as a compromise between lift and drag. However, you can use the same spreadhseet to develop a 0009 or a 0015 profile just as easily. In the spreadsheet, you'll just enter the last two digits of the profile pattern you want.
The last thing you have to do is insert your measurement points. The spreadsheet will calculate the 1/2 thickness at each of your points along the chord. so if you want a rough shape, you can just enter 1-inch or 1/2-inch increments, or if you want fine detail, you can enter as many increments as you'd like...
Anyone who's interested, just PM me your email address and I'll send it to you...if there was a way to post it here, I'd gladly do that...
Last comment - this is meant in no way to undermine what Idasailor (Rudder Craft) offers - they offer a fine product which many on this forum have praised. If you can afford to buy one, that's by far the easiest choice. If you're a die-hard do-it-yourselfer, or can't afford their products and want to tackle a project like this, I hope this helps give you a good tool to use.
Also, please note that there are many other factors that go into a proper rudder, such as material selection, etc. I have not addressed these because I'm not the guy to do that...
