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Ross 930 rudder ideas


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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!! :thumbdown:

 

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??

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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.

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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? :lol: :lol:

 

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.

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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.

rudeder.jpg

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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

post-234-141887176266.jpg

post-234-14188717627.jpg

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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.

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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.

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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.nwrdr.JPG

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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.

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