Hi Steve, Thanx for the interesting link. We’ve been studying "bumps" or “ serrations’ in nature for many years (our day job). We found they work well “ coming and going”. On the leading edge, they provide more linear inches of cutting surface as well as single point contact for penetration. A natural example would be the teeth of a shark. Early arrowheads mimicked these edges. Modern mimicry would be serrated blades on knives. In plants, they have similar functions in dissipation. On the trailing edge, they affect flow, such as the trailing edge of a bird ’s wings and tail. I’ve often thought about experimenting with serrated trailing edges on sails. Interesting thought you had on keels and rudders. (Maybe it’s time for me to contact Harry on the sails and pick Jerry’s brain on the underwater parts). Another example of sailing invention using mimicry: Back in the ‘80’s, Gail and I were selling an interesting boat called the "Sail Fin". It was a flat transom (for motor) canoe. It had a simple sloop rig with a dagger-board. The dagger-board had what was called a “Whale’s tail” fin at the bottom of the board. Similar to “wings” on some sailboats, but the “tail” was split and extended aft for about 2 feet. In addition to added ballast, the rear section was flexible and when the boat was rocked side to side, the “fins” worked like swim fins and propelled the boat forward. Used for trolling or moving location without motoring or sailing. sal 1985 M15 #361 “Justus” In a message dated 5/13/2011 4:49:56 P.M. Mountain Daylight Time, stever707@gmail.com writes: Here is an article from the Mechanical Engineering magazine that may be of interest. It describes how bumps on whale fins reduce drag. http://tinyurl.com/Whale-Fins If that link doesn't not work, search for "Whales" and "ASME". The bumps are on the "wrong side" of the fin from a conventional wisdom perspective. They allow a higher angle of attack before stalling. Unfortunately this is useful only in limited circumstances. I wonder if there may be a practical application to a rudder or perhaps centerboard. steve Steve R. M-15 #119 Lexington, KY _______________________________________________ http://mailman.xmission.com/cgi-bin/mailman/listinfo/montgomery_boats When posting, remember that there is no privacy on the Internet!