Rudders and Rudder Stock Stainless 316 329 or Aquamet(aqualoy) 22

Discussion in 'Boat Design' started by fpjeepy05, May 24, 2012.

  1. fpjeepy05
    Joined: Jan 2010
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    fpjeepy05 Senior Member

    I am told that it is best not to use 316, because it has a very low yield strength despite a high ultimate strength. 329 shouldn't be much more expensive, but I don't know if it has the same corrosion resistance qualities and weldability. Last option would be Aqualoy or Aquamet 22. I know it has the strength and the corrosion resistance, but I don't know about the weldability and I think it is also rather pricey. Is there there such a thing as Aqualoy 22 plate. I would need something around 1/2"
     
  2. CatBuilder

    CatBuilder Previous Member

    Is this a monohull or multihull? (does weight matter?)

    If sized correctly, 316L stainless (yes, with an "L") is the best you can do. The extra diameter stock will make up for the comparatively poorer yield strength.

    Also decent, though less resistant to corrosion is 15-5 or 17-4 PH stainless. It has 3x the yield strength of regular 316L stainless (at 60,000PSI), but of course will corrode more easily over the years.

    Pick your poison. Both a compromise.

    I chose the 316L, hollow tube to both save weight and be corrosion resistant, with a penalty on the yield strength.
     
  3. fpjeepy05
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    fpjeepy05 Senior Member

    I now also see SS 630 as an option
     
  4. CatBuilder

    CatBuilder Previous Member

    That is the extent of my knowledge on stainless, fpjeepy. I am trying to have as little of it aboard my boat as possible. :)

    We will have to wait for more people to pipe in.
     
  5. Stumble
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    Stumble Senior Member

    As an option, more and more rudders are being made with carbon fiber these days. Significantly lighter weight and flex but at a cost.

    Titanium is also an option, never corrodes, 3 times stronger than steel, and when designed properly not terribly more expensive.
     
  6. sabahcat
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    sabahcat Senior Member

    Speaking from experience ;) if I was you I would epoxy a foot of solid in the tube where it exits the hull.
     
  7. CatBuilder

    CatBuilder Previous Member

    ?? :?:

    Did you bend a rudder shaft?

    I'm confused. Missed the joke entirely... :confused:

    Are you talking about the rudder tube or the rudder shaft? I don't have a ruder tube on my design if that's what you are talking about. I have a kickup rudder with cassette. There are bushings that hold the shaft in place. If you torque it too hard, it pops up.

    I think maybe when I said "tube" I wasn't clear. I am using hollow 316L stainless tubing for a rudder stock. 2" dia, 1/2" wall thickness. I just ruined the joke, didn't I? :)

    PS (about carbon): Those inexpensive bushings you can use to hold a metal rudder shaft in place don't work with flexible carbon fiber. You also need to upgrade to special bearings that will still work when the carbon shaft is flexing as you steer. Otherwise, the shaft will jam.
     
  8. sabahcat
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    sabahcat Senior Member

    I had my 2" dia rudder shaft made from 316l with a 6mm wall for a 30ft cat.
    Yes, I hit the bottom, not very hard and bent the shaft and I had to disconnect that rudder as it could not be moved and motor home with the other one.

    Didn't know XXS existed in a 316L 2 inch pipe.
     
  9. CatBuilder

    CatBuilder Previous Member

    Ah, that sucks! Ouch! I don't even think I carried tools large enough to pull the tie rod shaft off my last (also 10 meter) catamaran. It's a good think you had them aboard.

    Yes, it's a 12mm wall thickness on a 48mm 316L tubing. It was made in Pennsylvania, USA, with the steel minded in Sweden by Sandvik. I got the best, so it would last.
     
  10. sabahcat
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    sabahcat Senior Member

    As was mine ;)

    I just made sure I had my boards down enough when playing in the shallows from then on.
     
  11. MikeJohns
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    MikeJohns Senior Member


    What type of craft and what type of rudder arrangement?

    316 is not very strong and it's a poor material for shafting where weight is a priority. Aqua... 22 is a much better material.

    In the commercial world a lot of high tensile steels are used to good advantage, epoxied and with either greased bearings or SS wearing sleeves they last indefinitely often with little care much better fatigue resistance and similar weight to what you'd achieve with Titanium alloy shafts! I have used these steels even on racing sailboat rudder shafts and often on cruising boats.
     
  12. sean9c
    Joined: Jan 2011
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    sean9c Senior Member

    You might look at this problem a different way. Start by calculating the load on your rudder shaft for your application. Dave Geer has the formulas in his book and also reprinted in Pro Boatbuilder magazine. Once you know the strength needed you can start looking at what materials make the most sense.
     
  13. Frosty

    Frosty Previous Member

    1/2 inch? I think thats your problem right there, mine are 2 inch.
     
  14. masalai
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    masalai masalai

    Or tubes/cylinders of grp made by the local fishing rod manufacturer but in LARGE size rudder tube at about 2" ID and the stock about 2"OD and honed to be a perfectly water lubricated match using an electric drill and rotating wire brush... KISS is good... a nice foil shape for the rudder blade - balanced for easy use, and a quadrant fabricated from metal and sleeved over the rudder to be bolted together (for replacement and repair capability) If you need a graphic, send me a PM and note to remind me to take some pictures of what I have done.
     

  15. CatBuilder

    CatBuilder Previous Member

    Again, Ouch! I know how much that grounding cost, then. :)
     
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