Initial Sea Trial Vibrations

2010 November 1
by Chris Brown

We always appreciate the opportunity to go on a sea-trial prior to starting any running gear work.  A preliminary sea-trial gives us the chance to see and feel the vibration first hand which allows us to start the diagnosis and also compare the before and after.

That was the case with a recent 120′ Intermarine that had a vibration problem.  During the sea trial is was apparent that the shafts and props needed significant work.  There are many different vibrations that can be felt and heard:  shaft hopping, propeller distortion and cavitation are just a few sources.  With this vessel we could feel the shaft hop and see the Tides Seal movement in the engine room – a clear sign of bent shafts and a misalignment.

Some vibrations are subtle and some are very bad.  This one ranks in the very bad category.  The video was taken during the sea trial.   We were about 2 miles off Fort Lauderdale in FLAT CALM SEAS.  Once the Captain pushed up to 1800 RPMs the vibration was obvious.  Everything in the aft cockpit was shaking and moving.  There is no way someone could sit around the tables  in the aft deck during a cruise.  A water bottle placed on the table shook and would walk off the table within 10 seconds.

The vessel was hauled and we are starting the disassembly process.  Stay tuned for updates on this vessel in future posts.

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