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Cracked propulsion shaft

Discussion in 'Props, Shafts & Seals' started by CalmSea, May 7, 2026 at 6:22 AM.

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  1. CalmSea, May 7, 2026 at 6:22 AM
    #1
    CalmSea

    CalmSea New Member

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    Dear colleagues,

    imagine you have CPP propulsion shaft OD 200mm with bore 80mm.
    Shaft has been found cracked exactly below ST seal assembly. ST is water cooled system. Cracks found deep around 1mm. Shafts are 20+ years old.

    Class has approved cracks repair by Belzona and shaft surface was checked only with regular NDT test. For example the Eddy current test never was approved by management for micro cracks check below surface cracks.
    Please see photos before and after repair.

    Your professional opinion would be highly appreciated!

    Attached Files:

  2. Capt Ralph, May 7, 2026 at 9:16 AM
    #2
    Capt Ralph

    Capt Ralph Senior Member

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    Interesting crack pattern.
    It goes all the way around? Reminds me of but welds joining pipe together,, failing.
    Oh wait,, CPP? Control rod down the middle?
    Was the shaft later x-rayed to ensure the welds went deep enough?

    I fear there is a problem with shaft support and sudden application of heavy torque loads.
    I am not a professional in this matter, just swamp logic; I would have no faith in that shaft.
    If it must be re-used, ease up on the rate of loading with your fingers crossed. ;)
    Last edited: May 7, 2026 at 9:21 AM
  3. LenR, May 7, 2026 at 6:10 PM
    #3
    LenR

    LenR New Member

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    Pay attention to harmonic issues also. It may be a minor issue and been happening for a while but that is the end.
  4. mapism, May 7, 2026 at 6:47 PM
    #4
    mapism

    mapism Senior Member

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    Amen to that.
  5. motoryachtlover, May 7, 2026 at 7:11 PM
    #5
    motoryachtlover

    motoryachtlover Senior Member

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    If the cracks had not been in a straight line would you guys be as concerned?
  6. Capt Ralph, May 7, 2026 at 9:04 PM
    #6
    Capt Ralph

    Capt Ralph Senior Member

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    Any crack is a concern.
  7. DOCKMASTER, May 7, 2026 at 9:12 PM
    #7
    DOCKMASTER

    DOCKMASTER Senior Member

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    Belzona does nothing for the strength of the shaft. All it is doing is helping to provide a continuous surface for the seal to ride on. Is the yard doing the work class approved to make shaft weld repair? Any certifications need to be specific to the material type of the shafts and the shaft size. Weld repair involves grinding out the crack, pre-heat, weld, post-heat with a specified heat reduction taper and then machining. We do shaft weld repair all the time and hold many class Certs. You could also explore spray metalizing which is now an approved process by ABS and NAVSEA. I think DNV accepts this now as well.
    CalmSea likes this.
  8. Capt Ralph, May 7, 2026 at 10:01 PM
    #8
    Capt Ralph

    Capt Ralph Senior Member

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    Here is a professional. Glad DM checked in with his knowledge :)
    CalmSea likes this.
  9. CalmSea, May 8, 2026 at 9:21 AM
    #9
    CalmSea

    CalmSea New Member

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    Thanks for your comment. I absolutely agree with you regarding repair, but obviously somebody loved quick repair while crew can't do anything about it. If you take into consideration this is CPP shaft with bore 80mm on shaft OD 200 mm, it means 60 mm shaft wall thickness. I believe any serious class especially IASC class would scrap this shaft. Bat in these days IACS is not any more what used to be.

    This shaft under load especially in bad whether easily can snap off and sink vessel and crew. This case telling you how is Yacht Industry polluted by any kind of dilatants.
  10. Capt Ralph, May 8, 2026 at 10:09 AM
    #10
    Capt Ralph

    Capt Ralph Senior Member

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    Capt, Exec and Engineer should all have a say in this.
    If you don't feel safe, find a boat you feel more conformable on.