The leeboards in "The $50 5Hr. canoe sail rig" book, as far as the streamline shape is concerned, looks like it would be easier to make than a balanced foil shape. For those who do not have the book the jist of it is that one side stays flat and you only shape one side. Which sounds reasonable to me since a piper cub wing is flat on the bottom and airfoil shaped on top. To get to my question.... assuming I were able to make a sufficiently efficient asymmetrical foil, would you want the flat side away from the hull, theoretically developing the "lift" to windward or should it be the other way? Also, if both leeboards were down at once would their combined efforts be canceled or would their combined efforts against eachother induce drag, thereby making the case for a symmetrical foil?

Thanks
Red

Yes, just as you suspect, the flat side goes away from the hull so the lift pulls the canoe to windward. Actually, it could be used the other way since airplanes with asymmetrical foils can certainly fly upside down. But it's a good deal less efficient. Also, as you say, two such boards in the water would cancel each other out. Not only that, but very likely produce more drag in doing so than a single symmetrical board.

Just from a construction point of view, I have to wonder how it works out to be easier. Since two such boards are needed, one ends up carving two curved surfaces anyway. If you can do that, you can just as easliy carve them on the same board and make it symmetrical. Am I missing something? I made a foiled board for my canoe. There was a lot of head scratching to figure out how to carve it but once I got that, it wasn't too hard to get an acceptable airfoil shape (I used the NACA 0010).

Beyond that, from a hydrodynamic point of view, this approach could be used to increase the canoe's efficiency to windward. But that's a topic that would need more discussion, I think.

Well, I plan to have 2 leeboards as it is, and only having to form one side of them seems to be easier because its half as many cuts, and no effort goes into trying to make it symmetrical. In my head the process goes something like this: pick some randomly small angle and cut from the leading edge to about 1/3 of the way back of the width of the board, cut a 45 degree angle from the trailing edge up to meet the other, run a router down the leading and trailing edge with the appropriate radius, blend in the rough spots then ...ta-da instant leeboard (lapsed time approx. 1 month at the pace I work). Repeat with a mirror image.

I'm trying to convince myself that there would be a measurable advantage to having the boards "lift" to windward, but I'd be willing to bet if I just got something to stick in the water I'd be doing alright.

I'm inclined to agree with your suspicion--hi-tech boards on anything but a hi-tech boat, like an IC, etc., will be of little benefit. Now, that being said, it's wise to round the front edge and taper the back to help the water slip past with little turmoil, but NACA planes, etc. on most boats will not be worth the effort.

Red,
OK, I can see where that seems easier since you'd planned on using two boards from the beginning. But I have to agree with Ed that it's not worth the effort. The strategy for getting the theoretical performance advantage out of cambered foils is complicated at best. But that's theory. I recall somewhere years ago coming across something about that approach having been tried on a big boat--some kind of bilgeboard arrangement. It turned out not to be practical. What the big boats do now for that is to have a flap or trim tab in the trailing edge of the fin keel to adjust the camber as needed. Seems a bit much to do that on a canoe, though.

If you could see your way to using a single board, having a symmetrical airfoil can help and be no more trouble than what you've already planned.

Ed,
The experience I've had so far with the NACA 0010 would lead me to disagree with you. My canoe's no IC. It's not at the high performance end but the low where it makes a difference for me. It's better "bite" to resist stall at low speed is so much better than the other boards I've had. Of course, that's a very subjective comparison but I'd definitely do it again on the next project.

Cecbell, what kind of boat do you have? I'm sure it has a lot to do with the hull, of course. I've used both flat and cambered and couldn't tell the difference, but, sailing a shoe is different than sailing a needle.

Now that mine restoration is almost done, I'm going to take photos of mine flat and heeled so I can see how much of my board on the weather side is exposed; I'm convince your average canoe (mine's an E.M. White) will benefit from two board due to the weather board being dry at times. I still stand by using two, half-way down, when running in shoals. Pics to follow!