-- Last Updated: Dec-24-12 12:57 AM EST --
Do you expect a keel to make the canoe more stable, as in being resistant to tipping? If that's your intention, I don't believe you'll perceive any benefit. It could even make it worse in the one situation where a sudden rolling action is most likely to occur and where it's also the most difficult to counteract, which is when suddenly encountering a swift cross-current for which you haven't properly prepared yourself by leaning the opposite way as the current wishes to roll you. In other situations, I don't believe a keel will supply enough surface area to resist a normal rolling action, and for simply "tipping over", as would be the action in normal lake paddling (getting cockeyed on the face of a steep wave, for example), a keel won't even "move sideways" enough in the water to help even if it had lots of surface area. The keel would have to stick very far down below the boat for the tipping action of the boat to generate enough "swinging" motion of the keel to provide resistance to that motion. That's just geometry. You can see this for yourself if you lay the boat on the floor and sight down along the proposed keel line while an assistant tips the boat, and watch how that line moves sideways relative to the floor during that tipping process. No lateral movement of the keel line relative to the floor illustrates no lateral movement of the keel line relative to the water that supports the boat. Of course, this demonstration isn't perfect because the rolling action on the floor won't be quite the same as when in water, because yes, when in water the keel line will move a very tiny amount to the left when the boat tips to the right, but the floor exercise will make it clear that this motion will be miniscule. After all, how much extra "swinging" motion from the keel can be generated when it's only embedded three inches below the water's surface?
Also, a boat with a keel can be pivoted, turned sharply and side-slipped pretty well, demonstrating that the keel isn't "grabbing" the water particularly well. I think a brace is your best tool for the job if you need to prevent tipping.