I have been fine tuning my asymm boards. They have a symetrical camber on windward side and almost flat on leeward side. Here's a clip of my boat with the old small sail and 2'nd gen. boards.

http://www.youtube.com/watch?v=Jn8fr0PaUqg&feature=related

I can sail up wing with one board or two boards in the water.

http://www.youtube.com/watch?v=spINFPjHH_g

Here are several different shots in this clip showing flow over boards. Some of the flows around boards are good others not so good

http://www.youtube.com/watch?v=eEevSrV04EQ

I think There is potential here. Just needs to be realy refined. I know my set up is crude.

Also the effect of having foward board down I think really matter when you have sails center of effort more forward. I found with my no so bagged out junk sail I need to set it further aft on mast and it seems the forward board is just drag But move sail foward on mast and use the forward boom line to sheet and hold leading edge of sail over to windward Like the wing sail on model the foward board down doesn't feel draggy. Just an feel or observation there is a deffinate difference just not sure why!? Force of sail and board in line vertical loading board up more possibly!? Also both boads need to be setup correctly in line running with out divergence in either one other wise its like drag a milk crate and no slop in connection between the two. You can see in the montage video mid way through one of the clips on starboard tack a look back at aft rudder thats out of alignment thats when it gets frustrating.

Dagger board and rudder that's two boards in the water. Two boards does make it slower the set up makes it slower. Yes I know my boat not fast by any means but it sure is balanced. Speed will come.

Todd

--- In harryproa@yahoogroups.com.au, Doug Haines <doha720@...> wrote:
>
> For me the rudder debate is only really about the shunting speed.
> I was shunting into a narrowing channel at Peaceful bay with a good swell running.
> I had dying light headwinds and had to make maybe 10 shunts into the tiny entrance at the end. It was an ordeal compareed to the "Todd" style slam boom bang shunt.
>  
> How would you sail in a bigger boat where things are bigger - well maybe the last Rob style will actually be pretty easy to raise nd lower, but is the idea of motoring getting too reliant on some more mechanical aids?
>  
> DOug
>
> --- On Sun, 1/8/10, JamesB <james.brtt@...> wrote:
>
>
> From: JamesB <james.brtt@...>
> Subject: [harryproa] Re: Leeway Prevention
> To: harryproa@yahoogroups.com.au
> Date: Sunday, 1 August, 2010, 18:48
>
>
>  
>
>
>
> I have "ogive" rudders which are symmetrical for and aft, but assymetric in the transverse direction. My boat does nowhere near 30 knots (about 13 or 14 top speed), but I find them to be very good. I mostly just sail with the aft rudder down as putting the forward one down just slows me down too much. Even with only the aft one down, I can still sail upwind reasonably well. There is also quite a bit of weatherhelm with the forward rudder down, but I have tried the same system on an RC model with an assymetric hull, and that seems to solve the weather helm problem just nicely.
>
> James Brett
>
> --- In harryproa@yahoogroups.com.au, Doug Haines <doha720@> wrote:
> >
> > you would't beturning to hard at 30 knots would you?
> >
> > --- On Sun, 1/8/10, willoughby_rick <rickwill@> wrote:
> >
> >
> > From: willoughby_rick <rickwill@>
> > Subject: [harryproa] Re: Leeway Prevention
> > To: harryproa@yahoogroups.com.au
> > Date: Sunday, 1 August, 2010, 17:47
> >
> >
> >  
> >
> >
> >
> > Dennis
> > If you are serious about getting to 30kts then you will need to give the rudders careful consideration.
> >
> > One immediate problem will be cavitation. A NACA0010 will cavitate at 3 degrees AoA at 30kts. The maximum Cd before cavitation will be only 0.23 for a rudder with AR4.
> >
> > The unique feature offered with two large rudders on a proa is the potential advantage of using asymetric sections for the rudders.
> >
> > I have taken a look at the possibility of using rudders with fore-aft symmetry but asymmetry beamwise at an Re 10E6. For example a NACA4512-15 section with AR of 4 will have an L/D of 22.5 and Cl of 0.4 at 0 degrees. By comparison the NACA0010 with AR of 4 will have maximum L/D of 16.8 but only 16.4 if you are doing 30kts before it begins to cavitate.
> >
> > Really you have two articulating keels rather than rudders. The actual control range is quite small because they will have plenty of power so you can use tall gearing. They will be very close to being in balance in either direction with the shaft centrally located. The pressure distribution is very even:
> > http://www.rickwill.bigpondhosting.com/NACA4512-15.png
> >
> > At 30kts you would need an area of 0.35sq.m to generate 17kN with Cl of 0.4 so each rudder would be roughly 0.3m long by 1.2m deep and 0.036mm thick. Without doing the sums, I expect this would be too small for the loads. So next iteration would be to work with a lower Cl and thicker section - say NACA3515-15.
> >
> > Due to the fine entry you will find that the Cd at zero lift will be similar to or better than a round nose rudder section.
> >
> > I have no idea if anyone playing with proas has tried asymmetric section rudders but there are not many of these boats competing seriously to bring out the best from the concept.
> >
> > Rick
> >
> > --- In harryproa@yahoogroups.com.au, Dennis Cox <dec720@> wrote:
> > >
> > > OK!  I am about to drill down to China.  (Hope that expression has the same
> > > meaning where you're from... I guess not... if you're in China)  I hope I
> > > can explain this without putting you to sleep... and hopefully you can slap me
> > > out of it.  There are two issues I want you to entertain... efficiency and
> > > strength.  We want to go fast... and we want to stay in one piece.  I think
> > > those are universal.  We are "thinking" about a HarryProa (nothing else really
> > > matters)...
> > >  
> > > Efficiency
> > > If you raise the front rudder, you have to kick the back rudder till the angle
> > > of attack (AOA) of the entire hull counters the leeward force of the sails.  We
> > > all know that low aspect foils are inefficient.  And the leeward hull is about
> > > as low aspect as you can get.  So even though its big and strong, there is a lot
> > > of side slip going on.  We are aiming for Europe and we hit Africa.  We also
> > > have a LOT of induced drag.
> > >  
> > > Now if we lower the forward rudder, we can get the two rudders (acting as highly
> > > efficient, high aspect foils) doing all the heavy lifting.  We can now set the
> > > AOA of the hull to be zero by having positive AOA on the rudders.  In this case,
> > > the hull is presenting the least drag it can possibly do and the rudders are
> > > taking all the load.  So we're kicking ass and taking names, until...
> > >  
> > > Strength
> > > ... you start realizing that we need to design for the "lifting windward hull"
> > > case.  As an approximation... the leeward force is about equal to the windward
> > > hull's weight.  Split that in two (for the two rudders) and for my
> > > case... that's 4000 lbs (17 kN).  (Forgive me Rob... you have the best
> > > pictures) http://www.harryproa.com/building_Vis/Vis_img_feb11.htm.  By the time
> > > you get the moment arms into the issue, the bottom rudder post would be taking
> > > somewhere around 11,000 lbs (50 kN).  I haven't analyzed these, but I think
> > > these supports would have troubles with that load.  Fortunately, they don't have
> > > to in Rob's design!  If you'll note the rudder isn't balanced so the lateral
> > > forces acting on the rudder are resisted... by... you got it... the helmsman. 
> > > If I were to take a WAG, I'd say Rob has a mechanical advantage somewhere around
> > > 100:1 on the wheel.  So to hold that, the helmsman would have to supply... 100
> > > lbs (500 N) On each wheel... not bloodly likely.  So, Rob has used the helmsman
> > > as a force limiting transducer.  Briliant!
> > >  
> > > Before I saw Rob's elegant brilliance, I was going to make my rudders
> > > (near) balanced.  I wanted some helm feel, but I didn't want a work out or blow
> > > the autopilot.  Then I realized using delicate members like Rob, I'd soon tear
> > > them off while sipping my afternoon tea and steering with one finger. 
> > >
> > >  
> > > Can anyone... tell me how I can have my rocket ship and eat it too?
> > >
> >
>

• New Members 4
• New Photos 23
• New Files 1