Daggerboard Design- a different perspective

[tspeer]

Originally Posted by Sean Herron

...I am just now mucking about with the idea of a shallow full keeled monohull with vertically lifted but asymetrical foils to pull the boat upwind...

Unfortunately, asymmetrical foils do not pull the boat upwind. They rotate the bow off the wind. Which may be beneficial in reducing drag or making the rig more efficient.

They also shift the keel drag polar so as to position the minimum profile drag near the operating condition.

But the lift on an asymmetrical keel and the lift on a symmetrical keel will be exactly the same. This is because the steady-state lift on the keel is determined by the sail trim, not the keel shape.

Giving the keel an asymmetrical shape will do nothing to make up for the lack of depth in the keel. That's going to increase the lift-induced drag and hurt windward performance no matter what shape the keel has.

Someone earlier said because you're a cat, you can have smaller foils as you'll be going faster.

While I'm no expert, maybe you should watch that line of thinking. There are some very unwieldy cats around created by designers who think that way. For a start, in conditions when boards are really critical (AFAIK) and/or highly loaded (light or heavy upwind) many cats are surprisingly slow. Secondly, through tacks, starts, and other manouevres they can be quite slow, and that's when you need a decent-size set of foils.

Gaining .001 on the straights through smaller foils won't get you back 30 seconds lost each tack. There are some boats around by big names that really struggle through manouevres and some of the best small cats have quite large foils.

I'm no designer but I've chatted design etc with some very, very good guys and this is what they generally say.