Tell me about T foil rudders.
Printed From: Yachts and Yachting Online
Category: Dinghy classes
Forum Name: Dinghy development
Forum Discription: The latest moves in the dinghy market
URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=12992
Printed Date: 28 Jun 25 at 8:14pm
Software Version: Web Wiz Forums 9.665y - http://www.webwizforums.com
Topic: Tell me about T foil rudders.
Posted By: iGRF
Subject: Tell me about T foil rudders.
Date Posted: 13 Feb 18 at 11:27am
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I guess they help dampen fore and aft pitching on short boats in chop, do they assist in early planing? I remember talking briefly to a guy with one on a national 12 at the dinghy show but we were more focussed on the gizmo he had on a gybing centreboard.
Then I guess there must be downsides if the boat heels badly won't they increase braking effect and turn dramas into crises during sketchy downwind transitions? (Gybing). Interested to hear from anyones experiences. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Replies:
Posted By: GybeFunny
Date Posted: 13 Feb 18 at 11:59am
| I think they are very good for clearing the floating weed from our lake in the summer. |
Posted By: 423zero
Date Posted: 13 Feb 18 at 1:03pm
| And using for a step. |
Posted By: turnturtle
Date Posted: 13 Feb 18 at 1:08pm
| brilliant for leg injuries when combined with wiring boats ... or catamarans |
Posted By: Ardea
Date Posted: 13 Feb 18 at 1:32pm
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A video of a study by the cherubs. Obviously only a snapshot, but looks to affect the flow coming off the stern. https://youtu.be/8T6WrPz-3jw" rel="nofollow - https://youtu.be/8T6WrPz-3jw also this: http://www.uk-cherub.org/doku.php/tech/t-foil_systems" rel="nofollow - http://www.uk-cherub.org/doku.php/tech/t-foil_systems
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Posted By: jeffers
Date Posted: 13 Feb 18 at 1:54pm
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A mate of mine who has a DCB design says the t-foil makes the boat far more stable in terms of pitching. Gives him the confidence to gybe in extreme conditions too due to the boat being much more stable. It tricks the boat in to thinking it is longer than it is. Whether that assists with early planing or not I don't know. There must be a drag element though (not to mention weed). ------------- Paul ---------------------- D-Zero GBR 74 |
Posted By: Rupert
Date Posted: 13 Feb 18 at 1:57pm
That'll test the glue joint! ------------- Firefly 2324, Puffin 229, Minisail 3446 Mirror 70686 |
Posted By: Daniel Holman
Date Posted: 13 Feb 18 at 2:38pm
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Graeme come see me and my shed at dinghy show I will run you through it.
Dan |
Posted By: iGRF
Date Posted: 13 Feb 18 at 2:44pm
------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: fab100
Date Posted: 13 Feb 18 at 2:50pm
Graeme come see me and my shed at dinghy show I will run you through with it. FTFY ------------- http://clubsailor.co.uk/wp/club-sailor-from-back-to-front/" rel="nofollow - Great book for Club Sailors here |
Posted By: Daniel Holman
Date Posted: 13 Feb 18 at 2:57pm
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Graeme,
First rule of tfoils, you don’t talk about tfoils. Second rule of tfoils, it’s always much, much cheaper and easier to achieve a similar end by making your boat a foot longer :-) Fab. Ha aha ah |
Posted By: Sam.Spoons
Date Posted: 13 Feb 18 at 3:06pm
What about t-foils and rudder gantries combined then, can we talk about those....... 
------------- Spice 346 "Flat Broke" Blaze 671 "supersonic soap dish" |
Posted By: Jack Sparrow
Date Posted: 13 Feb 18 at 3:27pm
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Basically - Energy recovery. You are effectively surfing your own stern wave as well as reducing the weight of the crew / crew displacement by placing your weight over the foil. BTW... to the forumite - thanks for the YouTube link. Shame the YouTube bar stewards have stopped paying advertising revenue for YouTubers with under 100k views! ------------- http://www.uk3-7class.org/index.html" rel="nofollow - Farr 3.7 Class Website https://www.facebook.com/groups/1092602470772759/" rel="nofollow - Farr 3.7 Building - Facebook Group |
Posted By: Daniel Holman
Date Posted: 13 Feb 18 at 4:07pm
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Pressure recovery is a very minor part of the gain, applicable to heavily rockered hulls at lower speeds.
It’s all about getting displacement out of the hull (typical dinghy resistance to weight ratio 1:10 at 10 kts) and onto the foil (l/d ratio ~ 30:1) at semi displacement speeds (so 6-12kts for dinghies) Above that speed generally the bow down moment of the rig means you can’t run the foil in positive so it’s just wasted area. Some pitch damping though. At high speeds or when beating Away, running in negative keeps the bow up on short boats with big rigs downwind, meaning you don’t compromise the hull design the rest of the time to make it surviveable in bear aways and hairy downwind stuff. |
Posted By: turnturtle
Date Posted: 13 Feb 18 at 4:35pm
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It’s good to know that with all these customisations the new boat will be so FARR out of class, that even you will accept there is no conspiracy around your own personal handicap...
Back to dinghy development, not PYAG bashing... hurrah! |
Posted By: Jack Sparrow
Date Posted: 13 Feb 18 at 4:59pm
I thought my post would drag you out of your tower. Now iGRF doesn't need to come to your stand. LOL. ------------- http://www.uk3-7class.org/index.html" rel="nofollow - Farr 3.7 Class Website https://www.facebook.com/groups/1092602470772759/" rel="nofollow - Farr 3.7 Building - Facebook Group |
Posted By: iGRF
Date Posted: 13 Feb 18 at 6:12pm
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Energy recovery I don't buy, nor can I see them doing much about keeping the nose up, but pitching dampening I can see, so could keeping the nose down on upwind legs into the sea. I also think the additional length offwind in marginal planing could help, especially if mounted back a bit on a gantry, but I'm not sure how class regs would view that. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: Jack Sparrow
Date Posted: 13 Feb 18 at 6:34pm
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It's fine in the class rules iGRF. But getting the right section / size for the foil will take some maths / experimentation. As will the adjustment system. Although Moths / N12's have done most of that work for you. Yes there is energy recovery. Yes there is reduced displacement. Yes there is pitch dampening. It depends which way you pull the strings. FYI... I was in N12's when this idea was first conceived. Conceived by an incredibly bright but back of the fleet sailor. Who's name escapes me. Who was widely ridiculed at the time by top of the fleeter's for his badly built experimentally rudder stock and therefor it's lack of ability to show it's performance gains. ------------- http://www.uk3-7class.org/index.html" rel="nofollow - Farr 3.7 Class Website https://www.facebook.com/groups/1092602470772759/" rel="nofollow - Farr 3.7 Building - Facebook Group |
Posted By: iGRF
Date Posted: 13 Feb 18 at 7:10pm
Eh?  Did I read that right? Have I died and gone to heaven? 
Bring it on, I can't wait.. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: Rupert
Date Posted: 13 Feb 18 at 7:25pm
That'll feel 2 feet longer! ------------- Firefly 2324, Puffin 229, Minisail 3446 Mirror 70686 |
Posted By: davidyacht
Date Posted: 13 Feb 18 at 7:29pm
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I think that I14’s were there before N12’s. Ref. Pressure Recovery, Frank Bethwaite talks about this with his Medium Dribbly NS14’s, by flattening the aft underwater sections the boat gets lift off the stern wave that builds up under the hull. I borrowed this idea for my Annie Apple N12 design. I also drew up a T-foil rudder using the I14 hub, but never had the courage of my conviction, though I did a study of the potential reduction in displacement due to lift, and there were marginal gains, I binned the idea because I calculated considerable drag at non optimal speeds. I think Graham Camm and possibly Tom Eddom had a go at T-Foils around that time, and the results at the time did not appear to be ground breaking. I think where the DCB gets it right is by using a low prismatic low drag hull form, and utilising the T foil to substitute for the hull’s planing surface. The adjustable pintle arrangement is also much neater than a pivoting hub that was the derigeur solution 15 years ago. ------------- Happily living in the past |
Posted By: iGRF
Date Posted: 13 Feb 18 at 8:18pm
Exactly ! Think I'll call it Pitch Perfect. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: craiggo
Date Posted: 13 Feb 18 at 9:36pm
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If you just want pitch stability you can go for much smaller foils and a fixed rudder as per the low rider moths.
If you want pressure recovery then vertical position of the foil is fairly critical. If you simply want to reduce displacement upwind then they need to be fairly sizeable as you will be looking to lift at least your weight off of the boat. Is the Farr a nosey boat? Doesn't look like it Will it go fast enough to benefit from pressure recovery? Not likely as it's a short high drag hull. Will the Farr benefit from displacement reduction? Probably ------------- OK 2129 RS200 411 |
Posted By: Guests
Date Posted: 13 Feb 18 at 10:47pm
Very good! By the way, it's damping not dampening. |
Posted By: iGRF
Date Posted: 13 Feb 18 at 11:19pm
I've read stories of pitch poling on Burghfield and on the sea, so yes, it is capable of them and somewhere else I read about the further back you can get the less likely you are to go over the front. I've always wondered why nobody has fitted nose foils on the bow to help stop that. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: Guests
Date Posted: 14 Feb 18 at 12:43am
| 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. |
Posted By: Do Different
Date Posted: 14 Feb 18 at 1:04am
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Firstly, hats off to you for committing to a new build boat. Secondly, a genuine question, dagger board, gantry & t foil rudder vs shingle and shore dump? Has something changed your thinking?
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Posted By: Daniel Holman
Date Posted: 14 Feb 18 at 8:25am
| Yes you have to be chest deep and holding the boat singlehandedly into a big shore dump to slot the tfoil in from underneath. |
Posted By: 423zero
Date Posted: 14 Feb 18 at 8:54am
| Thats the T-foil gone then, stick with the gantry, sods law T-foil is going to be a nightmare, you will always be conscious of it and it will spoil your fun. |
Posted By: aardvark_issues
Date Posted: 14 Feb 18 at 9:32am
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They predate T foils in Moths and they were a bad idea then...
------------- http://www.aardvarkracing.co.uk" rel="nofollow - Home of Rocket Racing |
Posted By: iGRF
Date Posted: 14 Feb 18 at 10:09am
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? ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: iGRF
Date Posted: 14 Feb 18 at 10:13am
------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: getafix
Date 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.... |
Posted By: getafix
Date 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? |
Posted By: davidyacht
Date 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. ------------- Happily living in the past |
Posted By: ifoxwell
Date Posted: 14 Feb 18 at 10:36am
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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 [TUBE]C060VoJSF-Y[/TUBE] ------------- RS300 |
Posted By: andymck
Date Posted: 14 Feb 18 at 8:25pm
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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 ------------- Andy Mck |
Posted By: Guests
Date 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 |
Posted By: Guests
Date Posted: 15 Feb 18 at 2:18am
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Posted By: ifoxwell
Date 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 ------------- RS300 |
Posted By: Guests
Date Posted: 15 Feb 18 at 9:01am
Peaky is right... The last cup they had a limit (3 degree offset) of rake on the rudders and the main windward foil couldn't be in the water. The rule was to stop the boats generating a huge righting moment through down-force with the windward foils (because of structural and safety risks). To get around this, the boats ran a bow down mode to limit lift from the windward rudder once up to speed. But more than just bow down, it was twist. The platform was twisted so the windward hull was more bow down allowing the windward rudder to generate down-force and righting moment, all whilst the leeward hull was much closer to horizontal trim. The hulls were pretty much one design, but the fairings were open. If they wanted to generate downforce from the hull (crossbeams) they could have just set the aero fairings up with that angle of attack with the hulls in horizontal trim. The bow down attitude was definitely a byproduct of specific rules and I don't think we know anything that specific about the new boat rules to conclude they'll do the same again. Read here from the section being https://boatingnz.co.nz/articles/how-we-won-the-35th-americas-cup/" rel="nofollow - "The balance of transverse forces" . Thee are some other quotes from the design team quoting the % of righting moment generated by twisting the hulls and the rudder.
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Posted By: andymck
Date Posted: 15 Feb 18 at 1:37pm
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We had a standard composite craft rudder.
I am sure jo Richards would talk to you about it. He is probably still a class member. Otherwise Tom S Andy ------------- Andy Mck |
Posted By: ThomasShepherd
Date Posted: 03 Nov 20 at 7:21am
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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. It will be pintle adjusted and plan A was to put the foil on the trailing edge, but I've been wondering since about putting it on the front edge out of any turbulence caused by the rudder blade. Now that's got me wondering about placement relative to the stern wave. The leading edge of the rudder will be hung off a gantry 9.5" off the transom. The rudder is pretty fat and going with the rear mounted option would put the leading edge of the foil about 14" off the transom. Should I go fore or aft mounted?
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Posted By: 423zero
Date Posted: 03 Nov 20 at 9:56am
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I would go fore, as you mentioned, it will be in cleaner water, will still have some turbulence from centre board. ------------- Robert |
Posted By: Granite
Date Posted: 04 Nov 20 at 9:20pm
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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. ------------- If it doesn't break it's too heavy; if it does it wasn't built right |