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Rotten Props??

Discussion in 'Props, Shafts & Seals' started by FIQ, Mar 8, 2016.

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  1. FIQ

    FIQ Member

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    Feb 19, 2016
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    Today I dropped of a couple of Michigan bronze 32X32 Props in to be checked.

    One of them had cracks on all four blades and he said that the other one was rotten.

    I've never even heard of rotten bronze!

    Anybody know what he is talking about?

    Can cracks be repaired?

    These were spare props that came on my recently purchased Navigator, so I thought to get them tuned up

    and stored in my garage.

    Maybe I have a couple hundred pounds of scrap!
  2. Capt J

    Capt J Senior Member

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    Take them to another prop shop and have them checked. I've never heard of rotton props. But it's possible the boat had electrolysis or something that has effected the integrity or the props.
  3. olderboater

    olderboater Senior Member

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    I haven't heard of that term but have read of props with cracks developing and not getting attention so that the blade was beyond repair.

    I've also heard of bronze when anodes and bonding aren't adequate gaining a pink tint as they basically lose part of the base metal and they go beyond possible repair. They generally show a lot of pitting and sometimes the drive components will show the same. If the anodes aren't doing the job them part of the metal of the bronze prop will sacrifice like an anode. If you hit the blade it will make a thud kind of sound instead of a ding.

    Still never hurts to get a second opinion.
    Last edited: Mar 9, 2016
  4. FIQ

    FIQ Member

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    Location:
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    When I purchased the boat, the props were down in the engine room.

    They were stood vertically, leaning against the hull on a piece of carpet.
    The edges of the blade on the carpet had some green corrosion as if saltwater had got to them in the past.

    Maybe he was thinking that some of the leading edges required too much repair to be viable.
    I've seen some pretty nasty props be restored, so I don't know about that.

    When I pick them up, I will ding them both with a ball peen to listen for a tone or a thunk.

    Maybe he would prefer that I spend $10k for new ones!

    I'll take them to Seattle for a second opinion.

    Thanks to you Captain J and olderboater!
  5. T.T.

    T.T. Member

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    Kruger and Sons in Seattle. Let the experts look.
  6. FIQ

    FIQ Member

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    I looked at the props after they were shot peened and they were both just covered with pink pits and craters!
    I remembered what olderboater said about zincs and bonding.

    After doing some research, I found that without proper zinc and bonding, electrolysis will leach the zinc out of the bronze and basically reduce it to a form of brittle brass.

    Doesn't sound like a good idea to hang something like that on the end of the shafts!
  7. olderboater

    olderboater Senior Member

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    Glad you figured it out. Sorry the answer is what it is. I hadn't heard the term rotten used to refer to them, but it sounds like a reasonably good description. Amazing how all the metals interact with each other.

    I'd suggest two things more. The obvious one is to maintain anodes. The other though is to check your bonding and double check for any stray current on the boat since you don't know over what period of time this occurred, whether on the boat or stored, or the conditions under which it happened. You just don't want it to happen again.
  8. Lepke

    Lepke Member

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    However you want to describe it, rotten bronze fittings are common on vessels that either don't get hauled often or have an electrical fault or both. I'd check rudders, thru hulls and any other in the water fittings. I've seen 36" props so bad you could break pieces off the blades with your fingers.
  9. Fishtigua

    Fishtigua Senior Member

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    Volvo's DPH 'G' series props were well known for this problem. Pitting was dreadfull and they ended up changed the "recipe" of the Nibral alloy.

    I used to run one of a matching pair of commercial fishing boats. On one boat they had a bonding issue and when the boats were hauled out, one prop was almost 2" smaller in diameter than the other one. The holes in it made it look like it had been hit by a shotgun!!!