T Foils

[Phil Alderson]

Using the push rod on the boat system,
6:1 is OK but a bit heavy to get fine adjustment when the boat is hammering
8:1 lead out to the racks is what I am using at the moment which is working well

[ghislain_devouthon]

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.

I have 4:1 on my twist grip which is a bit hard in heavy weather.

I'm thinking of a double system : 8:1 (or 16:1) on twist grip with a control on racks.

[Will_Lee]

Our double system was 6:1 on the rope and 48:1 on the twisty grip. The last 2:1 on the twisty grip was the ratio of the spindle (9mm) to the extension (18mm). The first 24:1 was rope.

The new system is likely to be 12:1 on both, but I may change my mind.

 

[smight at bbsc]

Is having two different mode of adjustments for fine and course adjustments?

[Will_Lee]

Yes.

[ghislain_devouthon]

To move forward and backward a 20 cm long rudder cassettes by 10° (+3 - 7) you need at least to have a 13 cm course.

Basically with a twist grip haveing a 2cm mandrel it means you will do 13/(2pi*1) ~ 2 complete turns without purchase.

As honestly I wouldn't do it without less than 4:1 purchase it means you will need approx 8 turns before going from 1 extreme to the other (bear away for exemple).

A faster mode with a big purchase and 2 blocks on racks would allow to release faster when tacking/gybing/bearing away.

Not sure to be clear ... 

[Stuberry]

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.

That's really interesting Kevin. I'll have to look at it closer when I'm back in the country.

[Ratface]

read through the thread but still hugely confused as what to do t-foil wise,
hope tomake one for my 14 not a full cherub sailor YET,

any help/ideas? and what would i be looking at spending if i made it?
and what system is best to go for?

Cheers

James

[Ben Howett]

Have you had a look at these pages?
http://www.sailingsource.com/cherub/test/doku.php/tech/t-foil_systems
http://www.sailingsource.com/cherub/test/doku.php/tech/t-foil_rudder

[paul_croote]

Great to here about another dog getting out regularly, Me and Tim were sailing at Chew, The evening started well with the fairing mod to the T foil working a treat, We now getting the speeds downwind we used to have before the T foil. Due to the weed at Chew we sailed the race with the standard rudder. Started ok but then it picked to big time. The down wind half was all 2 sail reaches, seriously terrifying. It got the the stage were we couldn't bear away without pitch polling. 91 sails would have been very welcome.

[dave_ching]

Our T foil works!
We know this because as soon as it tried to carry my weight it dismanteled the bottom of the stock.
It ripped the casset like a sheet of A4.
Oh well!
2 plans of action have resuted.
1. A stronger stock and we are going to build a complete spare stock rudder etc so we can just come in and replace it.
2. Try different T foil section.
Will, do you have any drawing section information on your rudder and T foil?
I think we would like to try something similar.

[roland_trim]

Dave,

Seeing as we're using a stock which Bloodaxe rated as "will last 2 minutes" I am keen to see some more failures to evaluate what the next stock will be. Do you have any pictures of the carnage?

R

[ghislain_devouthon]

My cassette seems to be bullet proof :

From inside to outside :

1 layer of 0/90 carbon/aramid 200 g/sqm
2 layers of UD carbon 200g/sqm
1 layer of 0/90 carbon/aramid 200 g/sqm
Some UD reinforcments at the top and the bottom of the cassettes.

The cassettes cross the tiller and is glued + 2 layers of biax carbon 300g/sqm

At the bottom the cassette cross a 1 cm carbon plate glued + 2 layers of biax carbon 300g/sqm.

[Will_Lee]

Our is two plates of at least 10 layers each - about 2mm thick and bagged. These have the shape of the rudder cut into them.

The sleeve is one layey of 300gsm 2x2 twill 0-90 weave.

[Will_Lee]

Paul Croote had a problem with Cheese: With the T foil on a speed limit was reached at about 13 knots. He suspected a too blunt rudder and root of t foil. He did a neat sharpening job on it and it worked!

Here's a couple of pics: