High-Speed Sailing

Next I'll discuss Greg Ketterman's Trifoiler and any similar craft. You can learn a bit about it at this address:
http://www.hobiecat.com/sailing/history_trifoiler.html
I don't have an address for a good site that gets into its design theory (how it works) but that should be available if you're interested.

Essentially the windward foil provides down-force while the leeward foil provides up-force. This dynamically balances the craft against the wind force. It is an outstanding solution to the normal imbalance of a sailboat's driving forces. It is rock-steady and brutally fast, I've seen it in action and I've talked to Greg. He did an outstanding job in its design, too bad it didn't sell well enough for Hobie to continue production.

Greg has seen my craft and we've discussed it a bit. I suspect he thinks I'm a wild-eyed na�ve inventor but he was a perfect gentleman. (I'm teasing ya Greg.)

Greg's design, as Longshot, skippered by Russell Long, did set a class A record at 43.55 knots. What are its chances for 50 knots? I think it's a dead end, here's why. While with clever fluid dynamics improvements and ideal conditions, I'm sure they could squeeze a bit more speed from it, it is a self-limiting design. As the wind velocity increases, the force on the sail increases, increasing the overturning force which is countered by the windward foil's down-force. This down-force transfers to the leeward hydrofoil which is also supporting the weight of the craft. At some point the lee foil gets overloaded and stalls out [cavitates]. (I assume the lee foil stalls [cavitates] first.)

I have a video of the Scientific American show "Frontiers" where Greg explains that they hit the drag wall at about 40 knots. (Yellow Pages was on the same show, by the way.)

Bob