excessive vibration mid rpms

[SV Tatyana]

I just recently had my 25d hauled and replaced the cutlass bearing, motor mounts and had the shaft/coupling/prop re balanced. After launching her I aligned the coupling to .003/inch however after a sea trial I'm experiencing a good amount of vibration around 1200-1800 rpms which wasn't there before. The engine is much smoother on the mounts and there is significantly less vibration at idle/low rpms and above 2000. I have since tried realigning the shaft to no avail. Is it possible the new cutlass bearing needs to be broken in as it did make quite a loud noise on land when I rotated the shaft? any other possibilities? I can't imagine spending another day in the engine compartment on my 25d!


Thanks,
Richard

[JWSutcliffe]

As with any dynamic system, changing spring rate to ground (i.e. new engine mounts) will alter the resonant frequencies. It is unlikely that the cutless bearing is the culprit, since the typical rubber lined bearing does not need any break in. Are you certain that the shaft is running true and centered in the bearing?

[Jeff and Sarah]

How long was the boat in the water before the second alignment?

[SV Tatyana]

I waited over 48 hours to do the second alignment, it felt like the shaft was pretty centered in the stern tube when I aligned but also difficult to tell for sure because of the dripless shaft seal not providing a little support before the shaft enters the stern tube. Any way to know for sure if it's centered in the stern tube other than just by feeling it out?

Thanks
Richard

[SV Tatyana]

Also wouldn't it continue to vibrate at the higher rpm if there was an alignment issue?