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Torsional Vibration Damages Tug Clutch
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PROBLEM
This customer had just replaced the friction plates in his forward and reverse clutches. The next morning they had picked up a barge and had headed out the inlet. Shortly after reaching full ahead, smoke began to fill the engine room. Unable to stop in the inlet, they had to proceed out several miles.
When the smoke cleared, they found the reverse clutch was red hot. After limping back into port, disassembly revealed severely worn friction material.
They checked their air control valves and circuits to see if they could explain why the reverse clutch smoked while going forward.
They couldn't figure out what happened, so they asked us to visit.
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SOLUTION
Within 24 hours, we were on site. Sure enough, a lot of friction material was missing, however the wear surfaces didn't exhibit normal rubbing contact. The air tube had literally burned at one point, yet the other metal parts did not have the expected "blueing".
After collecting all the data, we got on the phone with Ron Compton, who has considerable experience with similar propulsion systems. He gave us a couple more parts to the puzzle.
We then checked the pilot bearing clearance, and as suspected we found that it had opened up 0.008". Turns out that this particular engine and gear box has a critical torsional frequency near the full ahead speed. If the shaft is not properly restrained (proper bearing fit), it will whip. This action rapidly and violently throws the clutch plates back and forth, resulting in heat and impact failures of the friction material.
Due to the critical need for this vessel, we needed to get up and going ASAP. The bearing bore was bushed and machined to the proper tolerance. The center plates were cleaned and checked for flatness. The air tube and friction plates were replaced. By the next morning, she was back at sea.
If you have a problem which is tough to explain, give us a call.
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