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Tell me about T foil rudders. |
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iGRF
Really should get out more Joined: 07 Mar 11 Location: Hythe Online Status: Offline Posts: 6496 |
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Topic: Tell me about T foil rudders. Posted: 14 Feb 18 at 10:09am |
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Yes, If the rudder blade and the foil are a unit construction, but what if the horizontal foil were part of the gantry and fixed to a forward only direction? |
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iGRF
Really should get out more Joined: 07 Mar 11 Location: Hythe Online Status: Offline Posts: 6496 |
Post Options Quote Reply Posted: 14 Feb 18 at 10:13am | |
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getafix
Really should get out more Joined: 28 Mar 06 Location: United Kingdom Online Status: Offline Posts: 2143 |
Post Options Quote Reply Posted: 14 Feb 18 at 10:20am | |
because submarines surfacing or diving is only marginally impacted by the attitude of their external fins and a lot more about bouyancy.... |
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getafix
Really should get out more Joined: 28 Mar 06 Location: United Kingdom Online Status: Offline Posts: 2143 |
Post Options Quote Reply Posted: 14 Feb 18 at 10:32am | |
OK, I get the science behind that statement but.... A week or two ago I was chatting to a naval architect friend and he was speculating that 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? |
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davidyacht
Really should get out more Joined: 29 Mar 05 Online Status: Offline Posts: 1345 |
Post Options Quote Reply Posted: 14 Feb 18 at 10:33am | |
Do you have to slot the foil from underneath, the N12's have pivoting blades in stocks? I appreciate that the T foils act as a brake in the half up position. |
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Happily living in the past
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ifoxwell
Really should get out more Joined: 05 Jan 06 Location: Hoo Online Status: Offline Posts: 669 |
Post Options Quote Reply Posted: 14 Feb 18 at 10:36am | |
This was my take on it as far as 12's go... happy to be corrected if others think differently, I'm no expert on the subject
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RS300
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andymck
Far too distracted from work Joined: 15 Dec 06 Location: Stamford Online Status: Offline Posts: 397 |
Post Options Quote Reply Posted: 14 Feb 18 at 8:25pm | |
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 |
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Andy Mck
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Post Options Quote Reply Posted: 15 Feb 18 at 1:01am | |
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. The Bethwaites experimented with a bow mounted T foil rudder on the 49er. There |
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Post Options Quote Reply Posted: 15 Feb 18 at 2:18am | |
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ifoxwell
Really should get out more Joined: 05 Jan 06 Location: Hoo Online Status: Offline Posts: 669 |
Post Options Quote Reply Posted: 15 Feb 18 at 8:44am | |
Hi Andy Thanks for your input, what kind of profile do the DCB and other quick 12's use...? Ian
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RS300
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