Foiling rudder help

[STU W]

Got a foiling rudder to retro fit to boat but need to build stock for it. Before I do this can any one give me any help
what is the Max rake required from the horizontal forewards, does it EVER need raking aft?
does it always default to a vertical position, ie get swept back if not raked forewards? Hope that makes sense
how much does it need adjusting once set up for conditions and the leg being sailed
is there any geometric advantage to having the pintles move rather than the stock itself if you could remove stretch in any system used. Look forwards to any advice you guys can give. Got an idea in my head, well two but need this info before I can develop it further
Stuart

[STU W]

Anybody??

[Nick Copsey]

"what is the Max rake required from the horizontal forewards, does it EVER need raking aft?"
I remember reading somwhere that the 14's were using 7degrees +ve as their magic number for best performance, this is probably not far out from what we are using. the best way to find your optimum is to go out keep pulling more +ve on in a moderate breze untill you fell the boat star to slow then let it off a bit to go faster again, mark this as you max on position, on the boats i have sailed we have had a stopper so we can't pull more on than this.
how far -ve you will need to go depends what rudder you have your hull shape and your weight you probably won't need as much -ve as you do +ve, you only really use -ve when it's really windy.

"does it always default to a vertical position, ie get swept back if not raked forewards? Hope that makes sense"
again this depends on your setup but strong bungee definatly helps 
"how much does it need adjusting once set up for conditions and the leg being sailed"
again this vaires, rule of thumb is to leave it on you max on position unless it is pushing the bow down when you should be planning in which case let it off, it is always a good idea to have the controll line somwhere you can easily let it off going downwind if it's windy & gusty

"is there any geometric advantage to having the pintles move rather than the stock itself if you could remove stretch in any system used."
the advantage of not moving the pintles is simplicity, the disadvantage is it changes the ballence of the rudder as you change the angle and when you go to far off it would load up in the same way as sailing with a normal rudder half up, that is why i prefer moving the pintles. that said some people have setups where the pinltes don't move and haven't reported any problems. the other adavantage of moving the pinltes is you can put more travel into the system.
 
good luck with you project, don't forget these foils put a lot of load into the boat, they can amost support the weight of the whole boat and crew if you could balence it when it's windy, so make sure whatever you do with the pintles they are securley attached to the hull and your transom is strong enough, this is probably easyest if you make your bottom pintle the one you transfer the majority of the load through.
hope this helps
Nick

[STU W]

Thanks a lot for that great feedback Nick, anybody else had any different experience or ideas.
want as much feedback before I put pen to paper and then take it further
Stuart. 3246

[smilie]

Hello Stu, it made be worth asking Dare about is system with moving shock. Really simple and very easy to retro fit.

[Antony (Guest)]

Stu,
I have very little experience of using them but my impression is that it is all pretty simple:
6-7 degrees with a stopper so that is 'on'.  Leave it on and like that in anything over about 4 knots and sit on the lift it gives you.  When you feel the bow adopting the previously traditional downward trajectory offwind let it off.  If anybody ever angles the wing the other way then it is only by a very small amount to keep the bow up when it is really blowing but the benefit is at least partially offset by the way it slows you and loads up the rig into a gybe.
I do not really understand why all this does not create the horrible feeling you used to get sailing with the rudder not quite down but assumed it was because the foils are attached so that the vertical blade is forward of vertical a lot of the time and only goes back to about vertical.. if that makes sense.
I could be wrong - not yet even sailed one of my own so just a few goes in a borrowed one and a bit of listening over a beer or two....
Antony

[Steve (Guest)]

Antony,
The reason the feel or load through the tiller doesn't change as you change the angle of the wings on the systems widely used is that it is the "pintles" either top or bottom that is moved, so the distance from the axis through the pintles to the the centre of pressure of the rudder remains fixed. Raking the rudder in the stock to change the wing angle would change that distance and change the feel.
Steve
N3531

[STU W]

Thanks for the feedback guys. So Steve I'm guessing if I want the rudder to stay unloaded I anm better off adjusting the pointless rather than the stock. Has anybody actually tried just adjusting the stock and got any feedback how bad this loading is? 
Thanks again for all the imput to date
Stuart 3246

[Nev]

Stuart
Have you looked at the Discussion 'T Foil Rudder with Tilt in Stock - Concept Design'.
It seems to have most of the features you are looking for but is 'tilt in the stock'.
Cheers
Nev

[Nev]

Stuart
Attached are some sketches.
Cheers
Nev

[smilie]

With a bit googling you pretty much uneath all the past discussions of foiling rudders and there different systems. 
If found this

 http://www.national12.org/cgi-bin/Blah/Blah.cgi?m-1310377726/s-15/

with some decent photos of Dare's setup. What the photos don't show is there is a bungee and purchess hidden inside the tiller.
Also if you are planning on getting 'sticky' these guys have got some decent prices and what seams a pretty good service (subject to me getting my order without any hassel)