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[Torchy]

I've worked out it is to do with rudders...and is adjustable.

Is it like adjusting the angle of the engine on a speedboat ie controls the attitude of the planing hull?

[ThorneyBen]

Kevin Ellway has written a very good article which is on the main website but i think you have to be a class member to view it. Alternatively there are some pretty good articles on how to build them with some theory on how they work in the Technical section of the website too.

I will defer to other more experienced sailors here but for a brief outline though: in order to reduce the drag caused by the transom you give the t-foil a bit of angle which will lift the back of the boat. You then move your weight backwards in order to bring the attitude of the hull back to normal sailing position (except you will be slightly higher out of the water due to the lift). This gives a speed advantage in that the drag effect of the t-foil is far less than that of the transom.

Obviously, the faster you go the more you can load up the t-foil, this can have some interesting effects if you don't move back enough. See one of the recent pics of Atum taking a big nosedive upwind. Downwind it can save you from fairly disastrous cartwheels, but you have to make sure you let it back to neutral when you bear away.

Personally I have not really mastered the t-foil and until I am able to sail the boat well, I am sticking to keeping it neutral all the time.

[Torchy]

Thanks Ben,

I've found this on the website http://www.uk-cherub.org/doku.php/tech/t-foil_systems but your explanation actually has given me a better grasp of the basics as I haven't read it through in detail yet

...very clever

[phil_kirk]

The early T foils were said to be able to support 70kg at speed and as ben says are less draggy than the drag from planing without the foil at the same speed.  The modern T's probably create the same lift but with less drag. 

When the foil is working well the boat thinks it's that 70kg lighter but with effectively almost the same amount of forward drive.

[Torchy]

...so effectively the boat is  weightless - 70kg is the all up weight

[Born Slippy]

The two removable ballast packs need to be accounted for as well.

Total mass about 150-200kg depending on time of year, how much was eaten for lunch and toenail cutting.

[Torchy]

I was missing out the pie-faces...and I suppose a planing boat is already producing lift equal to the all up weight.

There's something poetic about the boat being weightless though...incurable romantic on a tech thread. Shall let the real engineers comment  :O)

[Stuberry]

The Idiot's Guide to using a T-foil by Peter Barton:

Upwind: Pull it on all the way, then move your body weight to trim the bow as normal. You will end up further back in the boat than without T-foil. Let some off when you run out of boat.

Bear away: Let a lot off...

Downwind: Pull on as much as you dare.

This worked well on Ronin, because the system was engineered so the max "on" position was with the foil producing the optimum lift/drag. On other boats it may be easy to have too much angle.

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