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C350 Vibration Noise Survey
Your vibration problem may have been the result of cavitation or some harmonic resonance due to the conditions at the time you experienced it.
With only 13 hours on your engine the vibration should not be the result of a worn cutlass bearing, which Catalina advised me is the most likely problem with some C350''s which have developed persistent vibration noise.
What happens is this. If the dripless shaft seal bellows is not properly compressed and bled of air when the boat is launched, an air pocket prevents cooling water from reaching the shaft seal as well as the cutlass bearing. This results in a very worn cutlass bearing in very short order, not to mention possible damage to the carbon graphite flange of the shaft seal. The vibration problem on my boat started after only about 60-70 hours on the engine. That was all the time it took to wear out a brand new cutlass bearing that was deprived of cooling water.
I replaced the cutlass bearing on my boat a week ago, and the vibration problem disappeared. Completely.
Catalina also has a water injection kit they can provide to obviate this problem. Make sure your newly commissioned boat does not have an air pocket in the shaft seal. In other words "burp" the shaft seal bellows if this has not already been done. This is critical.