Rudder Post Selection Thoughts?

Discussion in 'Multihulls' started by CatBuilder, May 23, 2011.

  1. CatBuilder

    CatBuilder Previous Member

    I am going to build rudders and dagger boards during the summer heat so I can keep on getting things done.

    This means it's time to get some rudder posts. I'd really like to stick with my plan of "no zinc anodes below the waterline."

    Does anyone have any input or suggestions on this?


    1) Can I put a stainless shaft under the water without a zinc if it's the only piece of metal down there? Sometimes, I will have an outboard leg down in close proximity as well.

    2) What are your thoughts on carbon fiber shafts? Suitability for home making them with prepreg, then sticking them in an autoclave? Cost for pro-built carbon shafts vs cost for home built, then autoclaved?

    3) Carbon suitability as a shaft material? Impact issues? (it is a kick up rudder), Years of service vs. stainless? Other thoughts vs. stainless?

    Thank you.
  2. michael pierzga
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    michael pierzga Senior Member

    Carbon works fine..Ive used carbon shafts for many years without problem. SS is also fine. cheap and effective. Your choice. Carbon and SS shafts are availbe pre built. Carbon shafts require extra detailing hence extra cost at the bearing.

    Check with Jaffa and Phils Foils

    Not much wet surface on a normal rudder shaft so anodes are not a big issue.

    Post your rudder design...kick up implies transom hung. A cartrige mounted rudder is simple and effective for a home builder.
  3. catsketcher
    Joined: Mar 2006
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    catsketcher Senior Member


    My stainless shafts have been on for 11 years and seem fine with no Zincs. I don't really know where I could put one if I wanted to do so. I check them every 6 months or so.

    A couple of tips from my end

    Tufnol is a good bearing material for stainless as it bonds really well to epoxy. This means you can insert the bearings into the rudder cassette. I had some sever space restrictions to work with and so needed the bearings inset some.

    You can make you own rudder tube by waxing the stainless tube and wrapping alight layer of glass over it. Run a knife up it to cut it off, prise it apart 2 mm and then glass the heck out of it. Getting lots of glass of a tube is tough.

    Your stainless tube may not be perfectly round - mine wasn't. I used 50mm by 5 or 6 mm pressure pipe.

    Go cassettes - I love mine but they are the second ones I made. Make your cassette slots slightly trapezoidal. DO NOT MAKE THEM SQUARE!. They will rattle and you may hate them . Make the slots tapered fore and aft and up and down so that when the rudder is in and down it is a totally tight fit. So make the slots first and then use the boat as a mould to do the cassettes. Now I can sleep.

    Consider making your boards in a female mould. The easiest way I saw was to use a steel sheet with a fold in it. The laminate was laid up inside the sheet and then bent around a strong piece of timber. The best thing about this is that you very easily make a board that doesn't bulge in the middle somewhat. My boards (glass over cedar) have a slight bulge in the middle where extra glass is laid. Even though I knew this would happen my boards don't like going all the way down. So be very careful about your boards and cases.

    When you put your case in the boat be SUPER careful not to compress the board case. I had an insert in mine but still I squeezed it ever so slightly which has led to a whole heap of issues later on . So tape a dummy plug or put the board in as you do it but keep the case open all the way. (MY cases are pretty flexy so this didn't help.

    As you can probably tell new boards are on my agenda. To make sure they work well I am going to use the sheet mould idea. It has been done on a few local boats that have big boards. I will then go out to Kankama before I glass in the strong post and check the darn thing goes up and down fully!

    Final thing - go big in rudders. There is a lot of hokum printed about cats not needing big foils. At least Kurt Hughes understands a cat has to lift its huge superstructure to windward. This is the job of the foils. My cats tack well and it is only because they have big rudders. At low speeds you need big rudders, in chop, after a tack and also out at sea when you are broad reaching one rudder will almost totally come out of the water. So don't reduce the size of the rudder. If there are any handling issues with sisterships - poor tacking etc - ask Kurt for a rudder design off a bigger boat and go large. Like grippy tyres on a 4x4.


  4. CatBuilder

    CatBuilder Previous Member

    I do know how to put zincs on shafts - you run a wire from the the top of the shaft/post, then put a through-hull zinc on the hull very close to the shaft. This works.

    Is that shaft the only thing you have underwater that's metal? What type of stainless was it?

    All techniques you describe are exactly what Kurt describes as the best way to go about making the rudders and dagger boards. Thanks for the input. You are in 100% agreement with Kurt on everything you posted. That's reassuring to me too, since I was going to follow all of his suggestions on the foils.

    I have seen those trapezoidal cassettes somewhere before (Farriers?) and wasn't sure what they were for. Now I know. I suppose I might as well do that to make sure things don't rattle.

    Phil's foils look good too, in case I go carbon on the rudder posts. Thanks for that link!

    I'm going to see what it would cost to have Phil's foils do the foils to save time. I wonder how much more than the materials, plus consumables it would cost for them to do the foils... interesting... but probably over budget! :)

    Thanks for the tips, guys. All good things to think about.
  5. sabahcat
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    sabahcat Senior Member

    Probably worth loading up some epoxy with 423 graphite powder and painting that on first before wrapping the light layer of glass around.
    It effectively gives you a graphite bearing

  6. sabahcat
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    sabahcat Senior Member

    Consider using the finished board as a former for a strip planked case

    I did mine using coreflute ( real estate signs ) with a few blobs of hot melt glue to hold it in place and some split garden hose down trailing edge and plasticine to fill/fair gaps.

    Wax and pva well
  7. catsketcher
    Joined: Mar 2006
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    catsketcher Senior Member

    Gday Sahbah

    I like the idea of using the corflute.

    I did use your idea of graphite in the resin to make the tube into a bearing. After locking up the rudders when doing 15 knots about 70 metres off Ballina bar and surfing in with the family on board I wanted better bearings. That said my tubes were not perfectly round so this didn't help. The Tufnol bearings were much better and I haven't locked the steering no matter what the load since. So I got better bearings and no knocking by making new tubes, bearings and cassettes

  8. AndrewK
    Joined: Mar 2007
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    AndrewK Senior Member

    Another option is glass tubes, you can get filament wound tubes at reasonable prices.
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