How do you connect SS rigging to an aluminum hull?

Discussion in 'Metal Boat Building' started by BillyDoc, Aug 9, 2005.

  1. BillyDoc
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    BillyDoc Senior Member

    Galvanic action? SS rigging on an aluminum hull?

    Electrically insulating the connection would be best, of course, but is it really necessary? Now that titanium shackles are available, is this an option that could be used between the aluminum deck and the stainless steel rig? Titanium is very “noble” but also forms a very tough oxide coating that is non-conductive. Does anyone have experience with titanium fittings used with aluminum at sea?
     
    Last edited: Aug 12, 2005
  2. marshmat
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    marshmat Senior Member

  3. BillyDoc
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    BillyDoc Senior Member

    Well, yes, but . . .

    Hey Matt, it ain't all that bad.

    Actually, the price of titanium seems to be dropping quite a bit. For example, a half-inch shackle with a breaking strength of 13,600 lbs is just $31.60 (US$) at the first place I tried (http://www.apsltd.com/Tree/d3000/e399.asp). I don't like it, but I can afford it.

    So, joking aside, is titanium a good idea for attachment to an aluminum hull? The strength is great, it's the galvanic action I'm worried about. And if it isn't a good idea . . . what is?

    BillyDoc
     
  4. BillyDoc
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    BillyDoc Senior Member

    Um, its been a week . . . does this mean that you can't have SS rigging on an aluminum hull?

    Did I ask a question too dumb to answer?
     
  5. marshmat
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    marshmat Senior Member

    So since nobody else has answered, I'll toss in my 2-cents worth. (DISCLAIMER: This is based on electrochemical principles, NOT on having tried it on the open seas.)

    If stainless steel and aluminum are electrically insulated from each other, they get along just fine. Easily accomplished with some urethane or silicone sealant and a couple of plastic bushings for the bolts.

    If they can't be electrically insulated from each other, just make sure there's a magnesium or zinc anode nearby that is electrically connected to both. (Check with your multimeter for continuity between the various parts.) The magnesium will then corrode before either the SS or aluminum is damaged, and it can be replaced easily.

    The oxide coating that forms on titanium (as with that on aluminum, and stainless steel) is not very conductive but will wear off at contact points, and so will not electrically insulate the parts.
     
  6. BillyDoc
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    BillyDoc Senior Member

    Thanks for your thoughts, Matt.

    It looks like I need to design some insulation in for my rigging attachment points at the deck and on the mast. Something I was trying to avoid.

    *sigh*
     
  7. D'ARTOIS
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    D'ARTOIS Senior Member

    Yes, I have. Titanium is a metal that is almost inert and alomost corrosionproof
    unless you call 1/1250 mm over 1200 years corrosion. I have done a number of tests with the combination of AlMg 4,5 and TiVaMn and other Ti alloys and the results were surprising.
    There is no interaction between Titanium and aluminium so to isolate Alu from the SSt you can simply use the Titanium shackle as an isolator.
     
  8. BillyDoc
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    BillyDoc Senior Member

    Thank you very much for that good news D'Artois! The titanium shackles aren't cheap (but they sure are strong) and using them will simplify the rigging nicely.

    BillyDoc
     
  9. johnW
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    johnW Junior Member

    How about using titanium clevis pins instead of shackles...about 1/3 the price.

    Just a thought.

    John Worsell
     
  10. Dutch Peter
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    Dutch Peter Senior Member

    You can anodize the aluminium and fit a ss bush in the hole.
     
  11. yipster
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    yipster designer

    viewing the making of QMII a steel/alu mixid alloy was used for welding alu deck to steel hull
     
  12. Dutch Peter
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    Dutch Peter Senior Member

    Was it called tri-clad? That's 2 layers of aluminium and one layer of steel forged together by an explosion.
     

  13. yipster
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    yipster designer

    making of QMII was on discovery channel yesterday
    but dont recall exposive forming or the name tri-clad
    but it probably was when it welds on iron and alu
     
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