Keel fins may be solid or hollow and constructed of reinforced plastic, plastic laminates, fiberglass, wood or metal. (Note: Strength and integrity of the keel fins must be maintained whether built solid or hollow.) Keel fin shape is not specified but must follow the general shapes outlined on the reference drawing. However, keels will not be less than 6 inches nor more than 8 inches long (Fore and Aft) at the keel/hull junction, nor less than 4 inches nor more than 6 inches long (Fore and Aft) at the keel/ballast bulb junction.
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The Mainwaring Keel shape is a fine choice!
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John Fisher suggests:
The quickest and easiest way to make them if you have access to a metal band saw is to draw the keel in CAD, then print it out. Glue that to a sheet of 3/32 aluminum with 3m77 and cut it to shape.
You could also do the same thing with sheets of plywood and layer it to achive a airfoil shape. Each layer should be smaller than the last and then sand to blend the layers. Could also make a good cad project.
Another way is to cut the shape in two pcs of 1/16 ply, then tape the edges together. Insert a couple of threaded rods between the two sheets for attachment. Then fill with epoxy and microballoons. Using this method you should also glass the outside for additional stiffness. There are photo's of making a rudder like this on the blog site.
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