Tell me about T foil rudders.

If you put it at the front of the foil then there is less of a moment arm pushing the bow down.

I have read that by having the T sticking out by about a third it means that the low pressure of the T is located at the high pressure area on the rudder. In theory it reduces the pressure gradient, and should be lower drag.

Posting here on an old thread as I'm building a tfoil rudder for my Farr3.7 . Not here to debate the pros and cons it may be a stupid thing to do from a race winning perspective but I want the experience of both building it and sailing it.

Originally posted by Peaky Originally posted by getafix   ...we might see rudders ahead of keels on the new monohull AC designs. The reasoning being that this would further enable the 'bow down' hydrofoiling attitude which he said improved aerodynamics (of the 'vehicle' when 'flying' through the air) and the lifting of the crew section of the hull (potentially the weightiest bit) out of the briney and to minimise surface area when in the air. thoughts? Hmmm, I don't see a general aerodynamic benefit to being bow down. The cats were bow down due to a rule limiting the range of play in the rudders as I understand it. Not sure I fully understand the rest of the argument - the lift of the combined foil set up has to be longitudinally in the right place, but that won't require a forward rudder. A forward rudder would be friskier though, likely leading to more small movements which is slow, unless a very good control system was fitted to filter out unnecessary action.

Edited by mozzy - 15 Feb 18 at 9:13am

Originally posted by iGRF Originally posted by Peaky Foils at the bow, like canards, are destabilising. if the bow lifts it will continue to lift, and if the bow goes down it will continue to go down. Makes you wonder how submarines ever surface when they reverse the bow plane?

Could give a long answer to that, but this ain't the place!

I first remember T foils appearing in moths. some of the later Magnum designs. These I think were fixed to try and reduce nose diving. I remember Simon Nelson trying a moth one on a N12 back then.
I think there is a big difference between N12 and I14 use of T foils. On the DCB we tended to have it switched on almost all the time. It did control pitch very well and you could induce a bow up position especially to get the nose over small waves before then going for more lift for a faster more level planing mode. This reacted very much in the same way as outboard trim on a RIB.
Once going it was just a case of sitting as close to the rudder a you could. As a result we moved back earlier. The boats with less rocker would need to back off of they had a nose diving tendency.
The dihedral swept back and up foil induced stability in a similar way to light aircraft. It also reduced the weed issues as a wiggle got rid of any. The N12 foils are set closer to the surface than I14, and I think at lower speeds the stern wave effect is important.
We rarely got to the point we needed to back off on the foil, which is not what I hear from I14 sailors who with greater speed can generate more lift. I wonder if the t foil reduces the extreme wheelies you see in 18’s
To get an idea of loads we were breaking fittings with about 500kg rating and the ones we ended up with were about double that.
We certainly got on the plane earlier and got longer than non t foils. It also allowed heaviier teams to be a little more competitive.

Andy