can you have too much lift?

[capt'n ron]

plans call for symetrical twin bilge keels. design does have toe in. could i put asymetrical foils in thier place(?) even with the toe in?. is the toe in there primarily because of the symetrical foils? i have read that even with assymetrical foils sometimes toe in is used, as well. vertical bracing/ stiffening/ strengthening keel box and intersection between hull bottom and box not a problem. is there such a thing as too much lift?

[tspeer]

You can't get too much lift. The leeway angle will change so that the lift will come back into equilibrium with the load applied by the sails.

The steady-state lift on the keel(s), rudder(s), and hull(s) always equals the side load applied by the sail rig and hull windage. To see that this is so, compare sailing hard on the wind with sailing dead downwind. Same keel, but in one case the lift is high and in the other case the lift is essentially zero. The difference is the direction of the force from the sails - to the side when going upwind and forward when sailing DDW.

What you can get too much of is drag. As long as the keels are operating below their stall angle of attack, the right question to ask is, "Given that lift = side load from the sails, how can that lift be provided with minimum drag?"

[Packeteer]

abridged quote from here: http://www.setsail.com/s_logs/deridder/dragon1.html

The asymmetric keels turned out to be efficient brakes, so we replaced them with symmetrical ones

[Skippy]

And one way to get too much drag is with too high an angle of attack. If the hull is crabbing to weather, that's definately more toe-in than is ideal. I would expect asymmetric fins to work very well, since the leeward on is ideal for lateral resistance and the windward one should provide righting moment without much leeward lateral force. The symmetric foils may have been chosen because they're cheaper to manufacture.

[capt'n ron]

thanks guys. the "restatement of the question does make sence and i never looked at it that way. this is a small ,but beamy trailer boat with very symetrical curve of areas. it's never going to get up, out of the water and despite it's beaminess, might possibly heel allot because of the fine aft waterline. derived max speed is only around 6 mph..... maybe the assymetrcals would drag her down. i was just thinking of little ways to stiffen her up as much as possible . i guess a guy could make both sets of keels and try them each, they aren't big and wouldn't cost much.