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Old 06-09-2018, 05:46 PM   #14
SeahorseMarineDD54201
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City: Zhuhai
Join Date: Jun 2018
Posts: 71
Quote:
Originally Posted by healhustler View Post
Oh, one other thing. In two similar cases where driveshaft “whip” was suspected to be the source of vibration, one shaft was replaced and the problem was rectified. The other was not replaced, but a mercury fluid balance ring (I believe it was only one ring) was installed on the 2” shaft at various locations until the vibration was eliminated in the regular operating RPM range of the shaft. It seems to me that the whip was noticeable at max RPM, but the device delayed the imbalance (and therefore delayed the whip) for an additional 500 RPM, which was all that was necessary to meet the performance expectations of the owner. Sorry for the lack of detail here, but I’m working with the memory of two old engineers. The mercury fluid balance ring was about $100 from this outfit:

DRIVESHAFTS

Very interesting device which I am not aware of.

As stated in another reply, I wonder if Thrust Bearing can support nearly HALF of the entire shaft from deflection. The shaft near the Thrust Bearing is the only exposed and short section (something like 1 or 2 ft, the rest is inaccessible in the stern tube), and may be the place to put this mercury device. I wonder if it balances against any deflection, or it could introduce another force that the Chinese shaft needs to bear with. So a brand name shaft would give a peace of mind for me.
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