Keel modeled and then redesigned, reverting to better centerboard shape

I was not happy with the long parallel sided keel with tapered ends. All my reading says that a foil shape will have less turbulence and more lift and while this may be a very minor issue in a small low performance boat, I think you might as well do something right or at least do a cost/benefit analysis to see if it is worth the extra effort. So I started looking at how one could make the lead casting and deadwood keel assume a NACA foil shape. Because it is very long and thin, a lower number 4 digit series foil would be the best choice. 

I chose a NACA 0006 foil with a maximum span of 6% of its length for the shoe keel. This resulted in a foil that is a bit fatter than the 8" wide parallel design in the last post. For the model, I built this using wood alone (as I did not have any lead or other suitable metal at hand) and attached a skeg using separate pieces of wood as well as shimming up the keel to allow for the curvature of the bottom. In the real boat, I would cast the lead in a plaster or wood mold made to the foil shape with rounded edges and a forward section that also curved up to the boat. The rest of the wood skeg would be made of laminated fir and/or plywood, glued up with epoxy and well sealed with epoxy and fiberglass. It would all be fastened to the boat with stainless steel bolts or rod and stainless steel screws as well as epoxy and fiberglass.

The other change I made was to revert to a tapered centerboard similar to my first design but a little bit longer. This helps reduce the bulk of the case in the cabin and makes for a more efficient underwater shape. I figured out that the complexity I was concerned with could be dealt with by making a series of plywood templates in decreasing cord (length) and width that a router would ride on to cut the changing profile. A straight board would required only two plywood templates of the same profile so this is a bit more work, but not ridiculous considering its double benefit. 

 Following is a sketch of the proposed modified keel and board. Note that it is different from what I built in the model, which used a fatter full NACA 0006 profile (see photos below). Once I completed the model I realized that the NACA 0006 profile was wider than it needed to be and fatter further forward. This would cause more surface friction than necessary, so I flattened the sides of the foil such that I still have enough lead to ballast the boat. The purple shaded area is lead and the green is laminated wood. I had to increase the depth of the foil to 3.5 inches from the 3 inch deep wider foil so as to have enough ballast.

Hopefully this is the final design! I took offsets (distance from a baseline) along the length of the keel that will be laid out on wood to get the curvy shape of the keel when building the real thing.

 

Model with keel and deadwood added. Note these are a bit deeper and wider than the final plan as I made modifications to the plan once I saw the model

Added some fairing compound.

I will likely paint the bottom next if I don't end up tearing off the keel and building a new one based on the latest plans.

Next steps are to build the centerboard and case. I will then remove the bottom from the strongback and re-do the strongback supports to support the bottom and keel turned rightside-up.