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[Will_Lee]

Basically, any more than 900mm is a practical problem. I recommend 900mm.

W

[Ghislain Devouthon]

My T-Foil is a moth rudder's one.

It is about 110 mm but really thin.

[Phil Alderson]

no wider than the boot of your car

[Stuart Hopson]

no wider than the boot of your car

Phil I drive a saxo, it will never fit in the boot no matter how narrrow the foil!

[Phil Alderson]

no wider than the boot of your car

Phil I drive a saxo, it will never fit in the boot no matter how narrrow the foil!

OK change that to the widest doorway.

[Ghislain Devouthon]

no wider than the boot of your car

Phil I drive a saxo, it will never fit in the boot no matter how narrrow the foil!

Just make me think when I get my international 14 from Archie Massey : he forced out the T-foiled rudder with fixed tiller from the back of his Subaru estate. I had then to manage to get it into my 307 CC   

I did Calais to Paris trailing the boat without any roof

[kevin_ellway]

Very nice! What do we think the optimum span of the T should be? as i'll be cutting down the prototype Atum Bom uber wide special soon.

I suggest there are 2 factors you need to consider as well as transport.

The first is the area of the foil required. The max L:D of the foil occurs at around a CL of 0.5 (5 deg for a symmetric foil). You can calc the lift from 0.5*Cl*1000*V^2 where V is the boat speed in m/s. To get say 70kg of lift at around 8.5 kts I think I recall that sum gives you about 0.1m^2. The windsurfer foils Will stuck on the bottom of the rudder are way bigger than that which would explain why they were draggy, so I suggest you chop some off the ends to give an area of about 0.1.

The second thing is that for a given area, increasing length (AR) lowers the induced drag. But if you place the foils 1/2 way down the foils like Phil to gain lift from the hull's wash, then there is no point in going wider than 900mm. The reason for this is that the zone of water affected by the hull is roughly a semi circle of 1/2 chine width radius extending below the hull.

Finally, to clarify a point often made, the thickness of the foil doesn't affect its lift for a given angle of attack. Thick foils can operate at higher lift coefficients than thin ones, but have a lower max L:D. You don't need really high lift coeff on a rudder T, so a thickness to chord of 10% is a good compromise. Laminar flow sections are also good. These tend to be a bit sharper at the front and have the thickest point at around 40% back.

[Phil Alderson]

Picture from SA showing how to run a twist grip to a push rod gantry system from RMW 14 at the dinghy show

[Will_Lee]

You can't see the above unless you are logged in to SA. Here is it for everybody.

I like the way this 14 does it. Like Atum they have gone for string-round-a-shaft method of controlling the Tfoil, but they have done some extra things - The string wraps round a few times and then continues so that there is positive control upwards and downwards. They also have gone (a little while ago) to using ordinary UJs and click-stop control, which I do not much favour.

My current thinking is twisty grip with a single line, but with less purchase (less than 48:1 that Atum had for the fine control). I am currently leaning toward s 24:1 with a fat (~25mm) extension to allow for more positive control. There will be dual control of string + twisty grip, but I am keen for the on-the-water control to be all on the twisty grip because it is so good adjusting it while flat out - especially downwind!

[ross_burkin]

Could anyone whip up a quick drawing in paint or somthing similar showing the route of the line? Pretty please?

[Will_Lee]

Sorry Ross, I don't know how it goes.

However, here is our own T foil progress, as of now:

(and, yes, I did need to take the workmate apart  to get the t foil out )

[Stuberry]

Random thoughts...

Using a T-foil with an adjustable flap at the back, like a moth foil, will have the benefits of the symmetric and asymmetric foil sections.

When the flap is centered the foil will be symmetrical and will have minimum drag in the light stuff.

When the flap is raised, to give lift, the section will be asymmetric, and give maximum lift for least drag.

Discuss...

[Will_Lee]

And easy and quick to actuate.

But difficult to build, difficult to organise the control system, hinge drag and hinge leakage.

[kevin_ellway]

To get the necessary range of angles, you would need a coarse adjustment of the whole rudder assembly and a fine adjustment for the flaps.

In principle, this combination will give lowest profile drag. To achieve this, you need an asymmetric foil with a flap. Tom Speer [www.tspeer.com] kindly did a design for me. If you want to build it let me know. All you need to do is reference Tom and let him know how it performs.

[Born Slippy]

Adjuster loads.

To start with (and to hit the target of foil by Keilder) we are opting for a  for a "pull string" adjuster for the T-foil for Slippy. Am I barking to think 4:1 will do me (that equates to 200mm of string from 0 to 10 degrees). What have people used before?

I know that 24-1 and 48-1 have been mooted for twisty grips and just remebered to chip in on this that remember the spindle diamer also has a big effect on the purchase of rope sysrtems.

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