Stailess Steel rudder?

Discussion in 'Boat Design' started by hargadoo, Jun 1, 2009.

  1. hargadoo
    Joined: Jun 2009
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    hargadoo New Member

    Hi All,

    I'm new here.

    I'm a metal fabricator -- machining and welding. Its recently happened that my rudder has started to delaminate and I'm gonna need a new one. For my boat, I've been quoted $1700 cdn for a new rudder with a foam core.

    What I'm wondering about is why don't people just fabricate a stainless steel rudder made from:

    -- Stainless Steel rudder stock.
    -- 316 stainless steel sheet folded over rudder stock and welded and re-inforced in places.

    The cost for the stock and sheet would be just $300 cdn in materials. In labor, hours-wise, it would take me approx 4 or 5 hrs to fabricate this rudder. It will be 3.5 feet long, hollow inside (doesn't matter if water is in it) and will have something at the bottom of the rudder to bolt on a zinc.

    The weight of the rudder would be even less than my current rudder. My current rudder weighs in at 150 lbs (I'm thinking it might be because its soaked with water??)

    It looks good to me on paper but I'm wondering if I'm missing something. Why aren't there more rudders made of stainless steel? Is there something I should know or have not accounted for when it comes to rudders?

    Thanks much.
     
  2. BeauVrolyk
    Joined: Apr 2009
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    BeauVrolyk Sailor

    Welcome aboard!

    There is nothing wrong with a metal rudder, even an iron one. There are thousands of boats out there that are made of metal and they do just fine. One reason that people tend not to use metal is because it takes some real skill to put compound curves into the shape. A rudder is usually not flat in any direction, and that makes it difficult for most folks to build in metal. This sounds like it wouldn't be a problem for you.

    Be sure you have a look at the types of stainless and their ability to live with salt water, include the rod you use for welding (as some rod isn't good with salt water either), have fun.

    Beau
     
  3. CDK
    Joined: Aug 2007
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    CDK retired engineer

    My boat has four stainless steel rudders alongside 2 props.
    The marine growth comes a bit faster than on the previous grp ones, but it is only a matter of maybe one or two months*. And the mechanical strength is of course much better.

    * I wasted money on a special product that is supposed to prevent marine growth on props and rudders. A dull gray coating from a spray can that looked good while the boat was on dry land, but it came off in flakes after 1 week in the sea.
     
  4. lewisboats
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    lewisboats Obsessed Member

    I built a blade just like that...slightly smaller at 18" long x 6 or 7" chord. I used stainless rod 1/2 at the front, 3/4" at the max chord and simply welded the two sheets together at the aft edge, welded to the 1/2" at the front and drilled a few holes along the 3/4" and welded through those to bond it. Oh and use 316L and TIG it if you can.

    Steve
     
  5. erik818
    Joined: Feb 2007
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    erik818 Senior Member

    Zinc and barnacles

    I have a stainless steel rudder on my wooden boat. Every fall when the boat is take up for the winter, there is a lot of barnacles on the rudder. Behind the barnacles are corrosion holes. After some decades the rudder is quite dented. There was a zinc anode on the rudder until this spring when I took it off.

    The rudder isn't galvanically connected to anything else, so the zinc anode was only "protecting" the rudder. The motor shaft (stainless) with the bronze propeller seem to be doing fine without zinc protection and there are no barnacles on them and not on the propeller axis bushing (bronze) either.

    According to an article in a Swedish boat magazine it could be better not to use a zinc anode at all with some metals. Some galvanic action from the stainless steel will keep the barnacles away, but the galvanic action is stopped by the anode. If the article is right there should be less barnacles on the rudder when I inspect it this fall.

    If the article I read is correct, a stainless steel rudder without galvanic connection to other metallic structures in the hull should be hostile to barnacles if the zinc anode is omitted. You are better than me to judge if the possible corrosion will cause any trouble before you can inspect the rudder after the season.

    Erik
     
  6. TollyWally
    Joined: Mar 2005
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    TollyWally Senior Member

    Erik,
    Quite an interesting observation about the barnacles. I would have never thought...
     
  7. BeauVrolyk
    Joined: Apr 2009
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    BeauVrolyk Sailor

    Erik,

    I have found that SSteel (which isn't steel, of course) doesn't like being "covered up". By that I mean that if it exposed to air, even the small amounts of air that is dissolved into the sea water, it doesn't corrode. You'll see evidence of this when you cover a piece of SSteel above the water line too. Where the air can't get to it, it suffers from pit corrosion. I'm guessing that the barnacles cover the surface of the SSteel and keep the air away, thus the pits.

    On bare SSteel below the water, I leave it uncovered by any form of bottom paint. I've had no pit corrosion doing this, although I do have to put a face mask on and scrap junk (barnacles and clams) off it if I don't drive the boat much. Movement seems to keep them from growing much more than any zinc/no-zinc or paint.

    One thing that did work for me was true lanolin, the oil from sheep. It was amazing. I smeared it all over the SSteel below the water line and a year later when I hauled it the lanolin oil was still there and there was no growth. I'm sold. You can get this in some marine stores, and I think you can buy it on-line from New Zealand, where I bought mine years ago.

    B
     
  8. Mercury
    Joined: Jun 2009
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    Mercury Mercury

    Steel rudder

    Hi,

    I was on some time ago discussing a new Stainless steel spray product, requires no heat, can be sprayed on or rollered. Product consists of 316L SS powder and a proprietary polyester binder. Possible to spray in almost any configuration, is extremely abrasion resistant and is used to protect the leading edges on wind turbine blades and airplane propellers. The company supplying this product is based in Temecula California. if interested I would be happy to pass on more details but do not wish to use this forum to promote any particular product.

    Terry
     
  9. Guest62110524

    Guest62110524 Previous Member

    on all my builds I use ss, I use 2205 stocks, 316 frames, in chord only and 316 skin
    i have never had an issue and it lets me use a smaller stock and therefore foil section
    I drew this in rhino, it has just been approved RCD UK
     
    Last edited: Jun 21, 2010
  10. ChrisN67
    Joined: Jan 2008
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    ChrisN67 Senior Member

    I have stainless I was thinking about making them thinners/ lighter... Any ideas?

    I was interested with less drag and lighter weight. These rudders are almost 60lbs a piece.
     

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  11. Mercury
    Joined: Jun 2009
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    Mercury Mercury

    Stainless

    Thanks for question regarding Stainless steel. There are a number of things you could do to lighten the load and still have Stainless as your finish. Take a different substrate material (fiberglass etc) Coat the substrate with Stainless steel which can be rolled on or sprayed. The coating will be approx. 7000ths and provide longer term hard wearing. Some are already turning to this material as a hull coating as it is so durable and need not be re-coated for many years.

    Hope this of assist, let me know if you want further info on the coating and where you can purchase.

    Mercury
     
  12. BertKu
    Joined: May 2009
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    BertKu Senior Member

    Hi Hardagoo and Mercury,

    Would there be an advantage to powdercoating the SSteel rudder or in my case also the keels? I assume that powdercoating will give some resistance to wear and tear.
    Bert
     
  13. Mercury
    Joined: Jun 2009
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    Mercury Mercury

    Hello Bert,


    The Stainless steel I referred to is not applied via a powder coating, rather it is a method of cold spray application which can be performed by roller and or automotive spray equipment. The SS is 316L which is a high grade corrosion resistant steel sutable for marine use.
     
  14. lewisboats
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    lewisboats Obsessed Member

    until you remove the ready oxygen from the surface. The chromium needs a steady supply of oxy to create the film of Oxided chromium which protects the substrate from corrosion. The whole reason the barnacles promoted the pit corrosion is because they sealed the surface away from oxygen. Your coating would suffer the same result...and why would you paint Stainless steel with stainless steel?
     
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  15. Mercury
    Joined: Jun 2009
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    Mercury Mercury

    Hello lewisboats,

    I thank you for your email and comments. You are of course correct when dealing with SS sheet metal. I was not advocating coating SS with SS although this has been done with good result (no corrosion or pitting), I believe what the original request was about included lessening his weight from 60LBS each rudder. What I thought I had indicated was the rudders could be replaced with a lesser weight substrate and if wanting the look of SS it could be coated with 316L encased in a hybrid binder (no corrosion). In the Channel Island Harbor S. California plates of stainless coated GRP have been in continual immersion where barnacles and tube worm etc. have attached over the time-line of 13 months, a simple pressure wash removed all attachment, what remained was a coating of SS 316L with zero corrosion or pitting of any kind. There is a video of same on You-tube, if you like I would be more than happy to see if I can find it.

    Thanks again,

    Mercury
     
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