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Shafts fail dye penetrant test.

Discussion in 'Technical Discussion' started by Hogfish, Apr 25, 2011.

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  1. Hogfish

    Hogfish New Member

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    Just hopped on board a new yacht while it was on the hard. Some unfortunate news came my way today. Any advice before I end up making my decision would be surely appreciated!

    E-mail goes as follows:

    I have some bad news. We sent the shafts over to the machine shop to have them checked for trueness and tto modify the length to fit the new engines. Unfortunately a dye penetrant test of the key ways show that Both tail shaft sections have cracks at the key ways.

    We can modify the shafts to length but there isn’t enough length to remove and machine the effected areas and still be able to use them in your vessel. That leaves only leaves two choices. Operate the shafts until which time they will break and then you loose the props and possible damage to the hull or renew the shafts. I can take the Captain over to the shop so he may witness the cracks if you wish.


    Thanks guys,
    Hogfish
  2. K1W1

    K1W1 Senior Member

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    Hi,

    As wasteful as it sounds I would be inclined to replace the shafts.

    You could reassemble it all and hope for the best but if the Owner has repowered as it looks from the comment about new engines the extra grunt might shorten the shafts life a lot.

    There might be scope to reuse them if the boat is going to be a dock queen but if not it would be something that nagged at me all the time when the conditions were right for the things to fail and as we know the bigger duffers never seem to happen when it is flat calm or during daylight hours.
  3. Hogfish

    Hogfish New Member

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    Thank you K1W1, makes more than enough sense. Thats about where I am at. Replacement time :cool:
  4. Capt Bill11

    Capt Bill11 Senior Member

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    I agree. You could use split couplers that clamp down on the shafts and add zincs to the shafts on the inside ends of the shafts to stop them from backing all the way out if they fail. (Which is not a bad thing to do in any case.) But after all the expense and time put into a repower why scrimp now.
  5. K1W1

    K1W1 Senior Member

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    Hi,

    How is the end of the shaft with the prop on it falling off going to cause the shafts to come out if they are still attached to the gearboxes?

    It seems to indicate in the first post that it is the coupling end that is going to be shortened and re machined as they say they can still shorten them but can't do anything about the damaged end and then say the props might drop off.
  6. Capt Bill11

    Capt Bill11 Senior Member

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    I guess I read it to quickly. I thought they were talking about the key way at the coupling end.

    Either way, go with new.
  7. Marmot

    Marmot Senior Member

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    If you have access to a competent welding and machine shop with good NDT capability, the keyways can possibly be gouged out, welded, and re-machined if replacement is not acceptable for some reason or if the cost is reasonable.