Vortex Generatos vs. Cross Keels

[Pat Ross]

I like the Cross 36 trimaran, but would prefer it with a shallower draft. I have been re-reading Thomas Firth Jones's book, Multihull Voyaging. On pg. 76 he give a brief line or two about Vortex Generators and reports success reported by others. Anyone done this? I would like to remove the Cross keel, reduce draft and replace it with the least complicated meachanism for leeway prevention when pointing. Up to this point I was thinking I would need to remove the Cross keel and put in a Dagger board box in the main hull, until I read about the Vortex Generators in Jones' book. Any ideas, experiences or comments? Thanks

Pat Ross
pat@multihulldynamics.com

[Pat Ross]

So here is an interesting link that addresses the very issue with a designer http://www.ikarus342000.com/Avorart.htm

Pat Ross

[rayaldridge]

You might also want to look up the work of Matt Layden, the designer of Paradox, a small cruising sharpie, which uses similar structures. He calls them chine runners, and he's evolved their shapes over several designs. He won the Everglades Challenge, an expedition style race for small boats, in the prototype Paradox, so the boat is quite fast for a heavy 14' monohull cruiser.

There's a good deal of controversy over these appendages, with some knowledgeable folks saying they can't work as well as their proponents claim. My take on Tom Jones' remarks regarding them was that he doesn't think they can possibly work, but it's hard to ignore Paradox. One Paradox owner/builder is also the owner of a fast multihull, and he has extensively tested his Paradox. He finds that the claims of good windward performance are not at all overstated.

As another data point, Layden's boat prior to Paradox was purchased by a cruising couple, Dave and Mindy Bolduc. They've cruised their boat-- Little Cruiser-- extensively. Unlike Paradox, Little Cruiser has boards for leeway resistance, and is a little larger. The Bolducs cruised the Bahamas in company with Layden for several months one winter, and reported that there was in most conditions little discernable difference in the two boats' windward performance. They said that LC had a small advantage in very light air, but Paradox had a large advantage in water too shallow for LC's boards.

In Layden's latest boat, Enigma, the chine runners have evolved into higher-aspect foils, and Layden reports that they seem to be an improvement over Paradox's runners.

Google "Layden" and "Paradox" for much more info.

Ray

[Pat Ross]

Ray,

Thank you for the help with the Layden work. I must have missed Tom Jones' comments, where are they?

[rayaldridge]

Originally Posted by Pat Ross

Ray,

Thank you for the help with the Layden work. I must have missed Tom Jones' comments, where are they?

As you mentioned, on page 76 of Multihull Voyaging, speaking of vortex generators: "When this technology reaches the aircraft industry, it certainly will make airport runways less congested." I took this to be a sarcastic comment, but maybe I was wrong.

Ray

[Pat Ross]

Originally Posted by rayaldridge

As you mentioned, on page 76 of Multihull Voyaging, speaking of vortex generators: "When this technology reaches the aircraft industry, it certainly will make airport runways less congested." I took this to be a sarcastic comment, but maybe I was wrong.

Ray

Yes I think you are correct. Thanks