Knowing you need aoa for best flow on different types of foil shapes. The foil that needs the least amount of aoa for best flow is again a compromise to over come the drag you describe as opposing force from each board if in deed this is the case.

The whole design goal of the linked boards hung on center chord was just that zero aoa for best possible flow, speed, along with a neutral helm. How controllable the set could be and what if any negatives there where. Everyone I talked to said the rudders would be over balanced and the set up would be uncontrollable.

So far in most all my shunts leeway is not even an issue. I'm am almost always on a lifted tack after a shunt.

I think its about refining the compromises. Not replicating the all ready known.

Todd

--- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@...> wrote:
>
> Todd
> With your AR around 2 they will have a best lift to drag just under
> 10. If you were to increase the AR to 4 then the best L/D is just
> under 15.
>
> To get the full benefit from the asymmetry you need to be able to
> trim them with respect to each other. You could set them up for
> close hauled but then they will have more lift AND drag than needed
> off the wind.
>
> They have similar performance to a NACA0010 section. The minimum
> drag is about 20% lower than a NACA0010.
>
> Rick
> On 07/08/2010, at 4:25 AM, tsstproa wrote:
>
> > RG14 mirrored...
> >
> > --- In harryproa@yahoogroups.com.au, "willoughby_rick"
> > <rickwill@> wrote:
> > >
> > > I have posted the co-ordinates for the best L/D rudder section I
> > can come up with for AR of 4 and Re# 10E6:
> > > http://www.rickwill.bigpondhosting.com/NACA_07-310.txt
> > >
> > > It is worthwhile noting that if the AR is not limited
> > structurally or by draft then the best L/D section will get
> > thicker. So if someone wants to play and can handle higher AR then
> > I can go through the exercise.
> > >
> > > The best L/D for this section occurs between 0 and 0.5 degrees AoA.
> > >
> > > It is VERY important to realise that they need to be able to have
> > relative angle trimming. If the boat goes best on the wind with the
> > combined trim greater than 1 degree into the windward side then the
> > blade area is likely too small to get the best L/D. Typically these
> > rudders will have the combined area similar to a centreboard and
> > rudder of other boats with the same sail area. With the Harry
> > configuration there should be a tendency to round-up with no
> > rudders until the ww hull unloads but these rudders are not going
> > to have much feel so there may be no indication of weather helm. So
> > it may require actually observing the angle of trim between the
> > rudders.
> > >
> > > The aim should be to trim the rudders to eliminate leeway.
> > Current aside, the boat should go where it is pointed. So the idea
> > would be to set a course and then slowly trim the rudders relative
> > to each other while maintaining the course to get the best speed.
> > Once this has been done a couple of times the best settings will
> > become intuitive for any particular conditions.
> > >
> > > These rudders will not have a cavitation issue for any reasonable
> > speed expectation - Cp less than 0.5 in best working region. If
> > thicker section for higher AR then cavitation would need to be
> > checked and the vortex shedding will be more significant.
> > >
> > > The vortex shedding should not be an issue on this section either
> > as the separation is only on the last 1 to 2%.
> > >
> > > Rick
> > >
> >
> >
>
> Rick Willoughby
> rickwill@...
> 03 9796 2415
> 0419 104 821
>