Nav wrote:
... Did you see the dihedral on current IACC
winglets? It's up to about 30 degrees (by eye). That neans when the heel
is 30 degrees (a typical 'powered up' design heel angle)

what? You need a new protractor. I din't see any IACC boats sailing at
heel angles of over 20 steadily, much less 30. And IMHO 12 ~ 15 is much
more common.

Anyway, I don't remember the details of the keel winglets this time
around, other than one whale tail design that looked cool but I don't
remember which boat it was on.


......The question I ask you to think about is
which one is controlling the keel tip vortex by a plate effect... The
answer is, of course, that they are too small to do that well and they
are really workin in conjunction with the bulb (that provides an
endplate effect). I don't think I'm giving TNZ design secrets away but,
what these long thin winglets are doing "flying" in the keel vortex
which is why they are at the back of the bulb. They extract lift and
energy from the vortes and increase overall keel efficiency. If they
actually generate a lift (or a torque) in a direction oppostite to that
of the votex then they rob it of energy and return energy to the keel
system (or reduce parasitic drag if you prefer).

Does the winglet no produce a tip vortex of it's own? And wouldn't that
counter the one from the main section of keel foil?

Anyway, this is a lot closer to what happens (as I understand it) than
what you were saying the first time around.

... Second they are not
symmetrical in section. The winglet with the negative angle of attack
generates less negative lift in the vortex than that with the postive
angle. The net effect is postive lift and again vortex energy robbing.

OK?

Dude, check your geometry. Each winglet may not be symmetrical, but they
are paired. The overall design *is* symmetrical. Any beneficial effect
they have on keel efficieny is in the area of reduced drag and increased
lift on the main keel section.

If the winglets prodcued net lift themselves, then it would be pulling
the boat down in the water, which would not help speed.

DSK

Cheers MC