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?

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?

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).

Tyler