Guest Posted March 20, 2011 Share Posted March 20, 2011 Well we had an awesome time out on the water in the BMW Regatta this weekend, unfortunately managed to have a bit of the rudder shear off at during the last race of the day on Friday. When i say a bit, i really mean everything that hangs below the water!! We managed to shape up an old scaffolding plank as an emergency rudder to get us to the racing and more importantly the party on Saturday but that too gave up on the last race of the day. So now a brank spanking new rudder is needed and there have been a few ideas thrown round on which way to go, classic lump of wood or flash it up a bit with a lightweight foam version, and of course different shapes. Any good ideas out there?? Link to post Share on other sites
w44vi 17 Posted March 20, 2011 Share Posted March 20, 2011 The class rudder is bloody good if you have the standard keel. If you go down the track of high lift low drag you may need to up date your keel but i'm no expert Link to post Share on other sites
wheels 543 Posted March 20, 2011 Share Posted March 20, 2011 The rudder gives you about 10% of the lift of your Hull. That is quite a lot. The type of design is a little...a lot out of my knowledge, because of class rules and hull design etc. But basically, the wideer the cord, the more lift (to a point) you get and more lift at slower speed of weater flowing over it(think Flaps on a Planes wing), but the more drag you create. The thinner, the less drag, but less lift. Certainly a shaped foil is better than something flat. A flat board actually has a lot of drag and turbulance (the two are interlinked) and very little lift. The point where this is mostly seen is when the rudder is trying to turn the boat. As the rudder incrases in angle to waterflow, a Flat board ends up becoming a brake in the water. The water flow breaks from the rudder surface at quite low flow speed and becomes a drag in the water. As soon as you introduce a shape, the flow speed over the surface (Laminar Flow) hangs in far longer and the rudder actually "holds on" before that flow breaks free and the rudder becomes a brake. The wider the cord (thickness) the more that holds on. It is very very similar to the sail. There are formulae available (NOAA) to work out what you want. What I suggest is you find out what is allowed in yoyur rules, then do a search on NOAA and if you fail to find what you want (because there is a lot of info), send me a note and I have the formulae here and can talk you through what to do. I would aslo say, for a small rudder, a Foam core is a simple means of construction. And yif you want to get really carried away, Carbon Fibre is actually not so expensive anymore. Link to post Share on other sites
Guest Posted March 20, 2011 Share Posted March 20, 2011 Mines all but 2 pieces now, but longitudinally for 'n aft, and is being held together by the gudgeon. You can have 1/2 if you like. Would you like to go real well to Stb or to Port? Mine will be receiving a strong treatment of carbon. Timber core I think. Try getting hold of Ian No Worries, he has a very sexy rudder of foam and carbon, I think. Link to post Share on other sites
Guest Posted March 21, 2011 Share Posted March 21, 2011 I did the new rudder on hot dogger within the class rules, works very well Link to post Share on other sites
Guest Posted March 21, 2011 Share Posted March 21, 2011 I saw that at FnG's shop - bleedin work of art. Link to post Share on other sites
Murky 1 Posted March 21, 2011 Share Posted March 21, 2011 It would indeed be hard to go back to a scaffolding plank after having seen the FnG version. Link to post Share on other sites
Changed 10 Posted March 21, 2011 Share Posted March 21, 2011 Talk to WT. He has avery nice moulded rudder on the Wild Thing. This is the one that I built, glass and carbon lay up, shaped foam core and carbon gudgeons. Bit of work for a novice though. Link to post Share on other sites
Guest Posted March 21, 2011 Share Posted March 21, 2011 Oh for f**ks sake!!!! Headsail envy, keel envy, cockpit envy and now f**king rudder envy. Will it never end Link to post Share on other sites
Changed 10 Posted March 21, 2011 Share Posted March 21, 2011 Grab some of that foam KM and knock one up before it gets too wet. Could likely shape it with the spade. Link to post Share on other sites
Farrari 4 Posted March 21, 2011 Share Posted March 21, 2011 The flat top main on AF looked very nice during the Panmure 2H3L Another thing to add to your list KM. Link to post Share on other sites
Marshy 30 Posted March 21, 2011 Share Posted March 21, 2011 The WT rudder is mint, i have one on the Mercenary. really good control. But it may be a touch small for a 930 i think... Link to post Share on other sites
Guest Posted March 21, 2011 Share Posted March 21, 2011 i would have thought that a 840 rudder would be a tad small for a 930 heres whats news new rudder inbuild next to her original, and finished Link to post Share on other sites
Changed 10 Posted March 21, 2011 Share Posted March 21, 2011 The Whats News was a very nice job. Beautifully crafted in fact. Link to post Share on other sites
Guest Posted March 21, 2011 Share Posted March 21, 2011 whts nws rudder inside a standard 930 class min box Link to post Share on other sites
Changed 10 Posted March 21, 2011 Share Posted March 21, 2011 That's a lot of drag. Couldn't it be tapered a bit? Link to post Share on other sites
Rhys 0 Posted March 22, 2011 Share Posted March 22, 2011 Yeah, FNG did a great job on our rudder. It was almost a shame to get it painted. If you need someone to build yours Lightfoot, you could do a lot worse. If one the other hand you want another scaffolding plank, well you can see our old one in that photo. Link to post Share on other sites
Guest Posted March 22, 2011 Share Posted March 22, 2011 The flat top main on AF looked very nice during the Panmure 2H3L Another thing to add to your list KM. You aren't helping nor was Grunt Machines sweet looking squaretop last weekend. My rudder is OK or will be when I glue the 2 halves back together. Thank god for strong strap type gudgeon's. I'm so tempted to Turbo but I have made myself a promise knot to change anything until I can do something I've as yet to be unable to do. Link to post Share on other sites
TimW 1 Posted March 22, 2011 Share Posted March 22, 2011 I have a real nice CNC Rudder mould. We have used it on numerous Multihulls and was also used on Positive Touch, a Young 30. (Although the first attempt at the Positive Touch Rudder broke as it was under specced, after our second attempt the Rudder has been great, the reduction in drag over PT old rudder is massive and it still has great control and never lets go. Link to post Share on other sites
Guest Posted March 23, 2011 Share Posted March 23, 2011 Hi Guys, thanks for all the input. Wheels I found all the formulas but it took a while to scratch the brain cells into action as it is 40 years ago when I learnt that sort of stuff. FMGs shape is where I am at. The way I sail and the charactoristics of the 930 means Murray Ross got it spot on first time. Actually mine was a bit fat and out of shape because it had been subject to battle damage some time in the past and and the repair was suspect which explains the failure. Link to post Share on other sites
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