Subject: Re: [harryproa] Re: new videos on youtube
From: Rick Willoughby
Date: 8/23/2011, 2:29 AM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

 

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
03 9796 2415
0419 104 821

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