Silicon Bronze Screws/Bolts with Stainless Steel Fittings?

Discussion in 'Materials' started by tontoOx, Mar 28, 2021.

  1. tontoOx
    Joined: Feb 2021
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    Location: Australia

    tontoOx Junior Member

    I am about to start buying deck hardware for the wood/marine ply boat I am in the process of building.

    I have read that silicon bronze screws/bolts are the best to use in a marine environment. However, what about using silicon bronze screws/bolts with stainless steel fittings (probably 316 but some might be 304)? I know that dissimilar metals in contact with each other can cause electrolytic action between the dissimilar metals and hence corrosion, but how bad would it be between silicon bronze and stainless steel? And are there any workarounds to deal with the problem?

    Thanks.
     
  2. rangebowdrie
    Joined: Nov 2009
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    rangebowdrie Junior Member

    I've not had any problems using silicon bronze fasteners to attach stainless deck fittings.
    But I would never mix metals for underwater use, like a seacock/thru hull/bolts.
    Don't use bronze on aluminum parts.
    The dearth of quality bronze deck hardware in todays world his highly lamentable.
     
  3. tontoOx
    Joined: Feb 2021
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    tontoOx Junior Member

    Thank you. I read somewhere on this forum:

    "A small amount of the more noble metal surrounded by a much larger amount of the less noble metal will result in a very slow corrosion rate."

    Q1. Would silicon bronze screws be less noble than stainless steel 304/316?
    Q2. Do you put something on the threads to seal the threads e.g. blue loctite thread locker?
     
  4. rangebowdrie
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    rangebowdrie Junior Member

    Silicon bronze is more noble.
    Standard practice is to coat the fastener with some kind of Polysulfide, and using the same as a "gasket" to bed
    the hardware part against its mounting surface,, no reason to have any "sealant" products on the parts of bolts/nuts that are interior and not exposed to weather.
    Sealant is for keeping water on the outside of the boat,, preventing leaks into the substrate/interior.
    No reason at all to use any kind of "Locktight" product(s) for anything of that nature.
    A complete discussion of sealants, their applications/usage, and properties approaches infinity.
     
  5. rangebowdrie
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    rangebowdrie Junior Member

  6. tontoOx
    Joined: Feb 2021
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    tontoOx Junior Member

    Thanks. Do you mean something like this for dipping fastener threads in?
    BoatLIFE Life Calk Sealant - 10.6 fl oz Cartridge | BoatLIFE https://www.boatlife.com/product/life-calk-cartridge/

    Okay, understand. I feel more comfortable now about using silicon bronze fasteners with stainless steel "deck" fittings.
     
  7. kapnD
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    kapnD Senior Member

    Does the above wisdom remain pertinent underwater?
    Say a SS strut, or a SS rudder with a bronze bushing/gland?
     

  8. rangebowdrie
    Joined: Nov 2009
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    rangebowdrie Junior Member

    The copper based metals are always superior in underwater usage,, (of course speed boats and outboards and all kinds of craft use non-copper metals in many applications,) I'm speaking to "traditional" craft used in salt water.
    Probably the most well known example of mixing metals underwater is using a bronze propeller on a stainless prop shaft.
    We allow that combo by the generous use of zincs, another combo that's common is bronze rudders with stainless shafts, and we monitor the corrosion, (or lack thereof,) by regular replacement of the zincs.
     
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