Hi Steve, As part of researching for a suitable boat I’ve read the articles about keel and foil design at www.vacantisw.com as well as your description of using a NACA 0000 foil shape with a 15% foil section in Offshore Cruising Encyclopedia. Can you tell me in general terms how much a foil shaped keel improves boat performance compared to one that has no foil, ie. the sides of the keel are parallel? Is this difference enough to warrant keeping away from boats without foil keels? Thx, DM
Hi DM: Foil shape – the foil itself, the planform, and how it intersects with the hull all play a part in drag. If you are motoring, or sailing downwind the issues are not as critical as when reaching and beating. And they are very significant.
I don’t think there is any generalized way to quantify this for you except to say that foil shape is as important as hull shape and sail shape. They are all related.
If you are interested at all in performance, then this has to be an issue. If you are interested in working your way off a lee shore in heavy weather it becomes a major safety issue. On the other hand, if you really like the boat, the price is right, and my two previous caveats are not important to you, then it is less of an issue.
Sounds to me like I have not told you much. As I am inclined towards performance, foil shape is critical to me. And we’ve spent a huge amount of time on this very subject for the unsailboat we are currently designing – to minimize drag. – Steve