Wouter,

Thank you for sharing your ideas!
I have played with a similar idea, but do not have the time or workshop to test it out.
My proposal is similar to Wouter's in the sence that the horizontal foil/winglet may pivot when the rudder kicks up, and it is fixed in horizontal position during sailing by a vertical rod inside the rudder.

However, my proposal is to fix the foil/winglet by having the Boyer-type kick-up push down the vertical rod. Hence, when you lock the rudder to down-position by fixing the kick-up rod, you simultanously fix the vertical rod in down-position and lock the foil/winglet. When the rudder hits the bottom, the kick-up rod releases and the horizontal foil/winglet will be unlocked and turn while the rudder kicks up.

This setup will not allow adjustment of foil/winglet angle during sailing. However, if the vertical rod is made of two pieces permitting screw-adjusted length, it will be possible to adjust angles with some device that rotates the upper part of the rod.

Catamarans ususally come with two rudders and designing a device that reliably works both rudders is not trivial.

I ask all you innovative sailors to report results if you try out any of these systems.

Stein

My system can only be adjusted when the boat is at a full stop and so only between races. It is comparable to adjusting your diamond wires tension. I is a tuning mechanism and not a trim mechanism. As the F16 class rules require I believe.

Can you make a drawing of your setup.

Wouter

I'll try to make the drawing next week - this one is overbooked with extra work (lectures).

The simple main idea is to have the kick-up rod - which is under some tension when the rudder is in down-position - push down the vertical rod which locks the winglet foil in horizontal position.

Stein

Stein,
Come on, be honest.
You just want the time to talk to Wouter's granny
before you do the drawings.

Wouter,

Attached are simple drawings (powerpoint).

Wouter,

Attached the other drawing.
(How do you attach more than one in each post?)

Stein

Hi guys, I've reading this thread and it sounds interesting.
I hope I can help a little so I thought of another setup for the T foils. So check out the attachment. This designs allows you to tune the exact force that you want to rotate the wing by means of a metal spring. Another advantage is that you can add this setup to almost any existing rudder by making a cassette that screws on to the bottom of the rudder tip, cassette containing the spring mechanism and the wing...
When the boat floats level the wing will realign and the spring will push the small rod into the notch of the wing pivot and secure it.
You think this design has a chance of working properly ?

I really like the principle.

Finding the correct tension that (1) DOES NOT release the foil when subjected to forces of 20 knots speed initiating a pitch-pole and (2) DOES release when tilting back the rudder coming to shore, will be the hard part.
But that may be a problem with the other solution as well, I suppose.

Stein

yeah, it allows you to tune the spring untill yo're satisfied
by compresing the spring on land and then sailing, the progressively compress the spring untill it's ok. It'll take a while to tune it, but it has less mulfunction chance then the rod through rudder design, I think...

I keep thinking magnets: If T foils pivot forward of mid-lift, with embedded permanent magnets holding the trailing edge up, then a kick-up at speed would overwhelm the magnets and disable the foil after a brief jolt.

Mechanically, it's a very simple release, requiring no moving parts. However, keeping them from locking down during a beach launch (where there's not enough speed to free them) might be problematic... unless one takes another crazy idea and glues an Alka-Seltzer in the way. :-P

--Glenn

I just found a very smart solution for the T-foil rudders on TheDailySail:

http://www.thedailysail.com/ism/articles...ment&Page=1

As you see the idea is to separate the foil from the rudder blade.
Doing so you can have the advantage of the T-foil without the disadvantages (read drag upwind).
For sure it is appliable (even if not very easily) to beach catamarans.

It was developed by the technicians within Baron Rothschild's Gitana team.
The secret weapon appears to be a T-foil, raisable in a similar way to an outboard bracket. This is mounted on the transom (aft of the rudder) of the starboard hull on the Gitana trimaran.

Link doesn't work Catfan !


Also you want to engage the T-foils on the upwind as well. Here they stabilize the rig, something most designers try to achieve by using lightweight carbon masts and lightweight sail cloths like cuben fibre. Interestingly, the better solution is to have two 100 dollar T-foils on your rudders. The effect is much greater and the expense much lower.

The only drawback I can establish with respect of the T-foil rudders as they are available now is traversing the surf. Ones that issue is solved then we'll all be sailing with them.

Wouter

Would it be acceptable per the class rules to have another appendage in addition of the rudder and daggerboard? I'm thinking some kind of retractable T-foil attached to the underside of the rear beam. This would make the T-Foil and the rudder independent of each other... Start from the beach, pass the surf, lower the T-Foil. The opposite on the way back.

Mmm, maybe it such an appendage would impact tacking because of the lateral drag it can generate during turns... It could have an interesting effect on weather helm as well. Not to mention what happens when you get a hull out of the water, I guess the appendage would have to be fairly long, or swinging from side to side...

Probably a stupid idea anyway <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

The link worked for me, but I only get the photo and the first two sentence of the article. The rest is for members only.

The photo is really explaining everything anyway.Direct Link to it.

So the Stealth already has the T foil rudders and the owners seem to love them, But have they had any trouble getting through the surf? I thought that with the casette rudder heads, they could just raise up the rudders to a shallow setting, say 6" down or so, on the way out and back in through surf, just as we all do now with our daggerboards. Is this not adequate to steer? Trying to steer through surf with your conventional rudders kicked up is pretty difficult already, how much worse could the casettes rudders down 6"-12" be?

Stealth owners, do you have any trouble with surf launching?

Next version of the kick-up T-foil/winglet rudder. In this version the vertical rod rotates 90 degs to engage/disengage the foil/winglet axel. The vertical rod (red) has a flange that engages a notch in the horizontal axel of the (blue in drawing) winglet. The Boyer-type kick-up rod (black) forces the the vertical rod in engage position when the rudder is in down-position. When the rudder is lifted or kicks up, the kick-up rod releases and the vertical rod rotates (elastic pull) and this in turn moces the flange out of the notch. Hence the foil/winglet is free to move with the water flow. Hope someone tries it! Stein

Next version of the kick-up T-foil/winglet rudder.

In this version the vertical rod rotates 90 degs to engage/disengage the foil/winglet axel. The vertical rod (red) has a flange that engages a notch in the horizontal axel of the (blue in drawing) winglet. The Boyer-type kick-up rod (black) forces the the vertical rod in engage position when the rudder is in down-position.

When the rudder is lifted or kicks up, the kick-up rod releases and the vertical rod rotates (elastic pull) and this in turn moces the flange out of the notch. Hence the foil/winglet is free to move with the water flow.

Hope someone tries it!

Stein

Prior to the Global Challenge I had never tried launching off an exposed beach into the surf with T foils. Although my very first attempt wasn't very successful (didn't let out the main and traveler enough, so screwed up; literally) My subsequent launches and recoveries went without a hitch. As you mentioned keeping the rudders down a safe margin made adequate steering very achievable without the hassle of the heavy helm experienced with conventional systems.

Mark,

I'd be very interested in the "chapter and verse" on launching in surf with our rudders, it's something I've ndot done and it does worry me.

Shouldn't there be a rule that says rudders have to be able to go through the surf?
Like in the spirit of being an of-the-beach catamaran?