Hi,

I have considered pivoting centerboard earlier. I still think it might
be good solution and a lot safer..
The rudders are 12% NACA and they are below the bottom of the boat. I
have plans to change their profile to athinner one and longer tapered
shape.
The daggerboards at the moment are cambered Speer proa sections.

Regards,

Arttu

> Arttu
> Gardner proposed a pivoting centreboard off the side of the lw hull.
> This was further developed to a board with a clevis off the side of
> the hull or off the bottom of the bridge deck (if strong enough) with
> a lateral brace across to the cockpit on the ww hull. (It would be
> nice to have the board under a beam but you do not want 2 boards).
>
> The brace will take large compressive force so needs to be large
> enough in section to avoid buckling. Also streamlined so it does not
> act as a brake when going through waves.
>
> The board can have a slight camber so it does not require leeway to
> produce lift. It can also be made bi-dirctional with small radius
> edges as it will only have a narrow range of working angle if sized
> properly (nominally zero or even negative). This will reduce
> intensity of vortex shedding with little risk of ventilating.
>
> The board can be pivoted up when running to reduce drag or for
> operation in shallow water.
>
> Need to give a bit of thought to the geometry of the brace and its
> mounting pivot so it allows the board to rotate while the brace stays
> aligned to flow (a universal or gimbal joint with rotation in two
> planes but still torque transmitting - outboard end a ball joint.
> The brace also needs to be bi-directional and non-ventilating.
>
> One observation I have made with brief experience with a proa is the
> impact of any hull fouling. The Harryproa hulls are low drag by
> virtue of low wave making. The viscous drag is contributing maybe
> 90% or more of the total drag - wave drag is thus close to
> negligible. This means the hull drag is much more sensitive to
> fouling than on most other sailing boats. So I have formed the
> opinion that keeping the hulls free of fouling will be rewarding in
> terms of achieving speed potential.
>
> I am not sure where it was mentioned but someone made the comment
> that they had operating rudder angles of 10 degrees. If they are
> NACA0012 sections then they will ventilate at this angle at higher
> speed or have a deep wave trough on the lifting side at slower speed
> - neither case is good for performance.
>
> Rick
>
> On 23/08/2011, at 3:35 PM, arttuheinonen@heinoset.net wrote:
>
> > I would like to have only one daggerboard in the middle, but the
> > mast is there. I really like increased upwind performance
> > daggerboards give. I can not see any other way to do this so far. I
> > am interested to hear any ideas. In my opinion rockerless hull
> > shape requires some board close to the middle to make it go straight.
> >
> > Regards,
> >
> > Arttu
> >
> > tsstproa [bitme1234@yahoo.com] kirjoitti:
> > > So four boards total to control the boat? Spiral up not down! Or
> > is this just an experiment to get variable control from different
> > concepts? I see multiple combination in controlling helm balance
> > with the two fixed and two steerable boards.
> > >
> > > Thanks for shooting and posting the vid.
> > >
> > > Todd
> > >
> > > --- In harryproa@yahoogroups.com.au, arttuheinonen@... wrote:
> > > >
> > > > Shunting is pretty easy. The harder the wind the better it shunts,
> > > > strange?? This is very clear also without the jib. With the
> > main only
> > > > the boat tends to steer upwind with less effort than to lee
> > side, IF I
> > > > use the rear rudder. With the front rudder this is barely
> > noticeable.
> > > >
> > > > BUT the rear rudder must be angled to make the boat neutral (10-15
> > > > degrees). It will maintain the chosen position bcause of friction.
> > > >
> > > >
> > > > Regards,
> > > >
> > > > Arttu
> > > >
> > > >
> > > >
> > > >
> > > > > Brilliant videos! Many thanks. Please keep them coming. Speed
> > looks to be
> > > > > 10 knots on the chart plotter? Wind about the same judging by
> > the lack of
> > > > > white caps? How easy was it to steer and shunt with only the
> > main?
> > > > >
> > > > > rob
> > > > >
> > > > > On Mon, Aug 22, 2011 at 2:46 AM, Arttu Heinonen
> > > > > <arttuheinonen@...>wrote:
> > > > >
> > > > > > **
> > > > > >
> > > > > >
> > > > > > Hi ,
> > > > > >
> > > > > > I uploaded two new videos on youtube. On the first one you
> > can see how our
> > > > > > mast
> > > > > > is bending. There is significant intentional twist on the
> > main because of
> > > > > > strong
> > > > > > wind. We had to furl the jib soon after this. The speed was
> > then 7.5 knots
> > > > > > upwind with the main only.
> > > > > >
> > > > > > http://www.youtube.com/watch?v=MOX1YkTrv5c&feature=related
> > > > > >
> > > > > > On the other video you may see some overall appeareance of
> > our boat. There
> > > > > > is
> > > > > > lots of main sheet . We changed the main sheet to 1:2 and
> > installed extra
> > > > > > tying
> > > > > > points both for the sheet to attach and for tying up
> > purposes. I think it
> > > > > > wprks
> > > > > > now better. It is easier to handle winches now with the
> > main sail only,
> > > > > > forces
> > > > > > are lower.
> > > > > > http://www.youtube.com/watch?v=C0SagTSVrL8
> > > > > >
> > > > > > regards,
> > > > > >
> > > > > > Arttu
> > > > > >
> > > > > >
> > > > > >
> > > >
> > >
> > >
> > >
> >
> >
>
> Rick Willoughby
> rickwill@bigpond.net.au
> 03 9796 2415
> 0419 104 821
>
>