winged keel

[drunkensailor]

I hope this isn't a dumb question but does anyone know if extending the small wing on the rudder the entire length of the keel would make pocket ship less likey to roll over? I've noticed most of the new Catalina sailboats use a winged keel.

[mtsailor]

Don't know if you'd gain much additional stability by putting a wing on the keel. I'm thinking a wing would make the boat difficult to roll over when needing to work on the bottom. The wing would have to be mighty strong to take the stress of the boat laying on it. John did a good write-up on the PS design stability a while back on this forum. Good info when considering design changes. Good luck. Jer http://gallery.me.com/jermcmanus

[John C. Harris]

A winged keel has two distinct purposes, one related to hydrodynamics and one related to center of gravity.

Hydrodynamically, the fins keep water running aft across the chord of the keel, rather than allowing some of the water to sneak under the keel. This means that all of the keel is generating lift to move you to windward, whereas the bottom part of the keel is otherwise lost to turbulence. So you can make the keel smaller for a given amount of lift, and thus shallower. (Or, if you're a jet airplane, you can make the wings shorter for the same amount of lift.)

While you're putting winglets and things under the boat, if you make them out of lead, the boat gets more stable. So that's why you see it on cruising and racing boats.

All that aside, it isn't worth doing on PocketShip. The keel isn't deep enough and the boat isn't fast enough to reap the hydrodynamic benefits. (It works great on the rudder, however.) PocketShip's centerboard is there to do that work. The wings would be fragile when it came to trailering or beaching, and they'd add a serious amount of wetted surface that would cut down on speed. And as far as adding more ballast on the bottom of the keel, that's a huge pain in terms of construction, and you can't add it just anywhere without lousing up the boat's trim.

[drunkensailor]

Apparently that was a dumb question. Thanks for all the input though. I think I'll stick with pocketship as is. I'll be lucky if I can build it properly let alone modify it.