Metal fatigue

  • August 30, 2012 7:46 AM
    Message # 1060562
    I am soon to replace my old wooden boomkin with one of Bud's stainless ones, but I have noticed that with the old setup, with the engine running, there is considerable vibration in the boomkin tangs. Given all that I have read on the forums about these tangs failing, I wonder, how much of those failures are due to metal fatigue rather than corrosion?
  • August 30, 2012 2:45 PM
    Reply # 1060991 on 1060562
    That sounds off.  Have you checked your motor mounts lately?  It shouldn't vibrate that bad.  Also, if you have the engine room liner, have you secured it as per Bud's manual? 
  • August 31, 2012 12:10 PM
    Reply # 1061774 on 1060562
    I don't believe my engine is causing any more vibration now than it has previously, but I have to admit that since I bought the boat in 2008 I have little basis for comparison. What I am referring to is the tendency of the cables on the tangs to vibrate like a guitar string whenever the engine is running. Does that not happen on others' boats?
  • August 31, 2012 12:15 PM
    Reply # 1061779 on 1060562

    I'll check next time we go motoring but I don't recall every noticing that sort of vibration before which is why I was curious about your motormounts/etc

  • September 04, 2012 6:36 AM
    Reply # 1064068 on 1060562

    From what I hear is that your boomkin tangs may be too loose.  If they are in a harmonic with the engine at idle, then they are certainly too loose.  Else, I believe that minor displacement of the boomkin tangs would not result in high cycle fatigue, especially with stainless. 

    If I received one of these failed tangs, I could make a micro sample to search for "beach mark" which would signify high cycle fatigue.  The more concerning question is if it is due to bending (engine vibration), or if due to tension loading (loading the backstay).  The answer to this question can only be found in a micro sample.  Since fatigue is subject to temperature, material, surface quality, stress risers (square notched hole), etc, we cannot rule out bending damage, but my analysis rests with Bud and that the boomkin tangs were originally under sized by width (if not thickness as well).


  • September 05, 2012 6:28 AM
    Reply # 1064943 on 1060562
    Deleted user


    I checked for vibration when out this weekend and there is a little at the lower RPM ranges and at idle power. It is not a high frequency vibration like a guitar string more like a little shaking is the best way I can describe it. I have the old MD11C and minor vibration is certainly evident in certain other parts of the boat as well. I did replace the boomkin tangs with the more robust ones from Bud and keep the wires pretty taut.


    Last modified: September 05, 2012 6:29 AM | Deleted user
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