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Old 09-26-2018, 01:46 PM   #7
kapnd
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City: hawaii
Vessel Name: #31
Vessel Model: ex-Navy MUB 50 fish/cruise
Join Date: Aug 2013
Posts: 869
Quote:
Originally Posted by O C Diver View Post
Several factors can be causing your problem. First a traditional stuffing box may have cut down the wobble so that you didn't notice it. The wobble that appears above a certain RPM may be caused by several different things.

First, you realized engine alignment was a partial cause.

The propeller can also cause wobble if one or more blades is slightly out of pitch. Growth (barnacles) on the blades can cause an imbalance.

You could have a worn cutlass bearing that doesn't cause the shaft to jump until you reach the magic RPM.

You could have a slightly bent shaft.

The objective is to figure out what is causing the problem through analysis, not monetary injections. When next you haul out, I would pull the prop and have it scanned. This will tell you if it's true or needs to be reconditioned. Most prop shops will do this for a small fee or less. With the prop off, I would check the cutlass bearing for play by trying to move the shaft up and down, and side to side. If there is play and you don't know if it's too much, seek a professional's opinion. I would also then consider pulling the shaft and coupling, and take them to the prop shop for analysis. Is the shaft bent? With the coupling locked on the shaft, does the coupling face spin true to the shaft? Hopefully, without having spent much money, you can determine if any of these things are causing or contributing to the problem. While you're at it, check your motor and transmission mounts. A broken or worn out mount can be the problem.

Ted

If you take the shaft to a shop, be sure to take the propeller, key, and nuts, so they can check it as a system, rather than an individual part.
Vibration can occur, even on a perfect prop if the taper and key do not fit precisely.
Also note that props installed underwater often do not receive the same degree of scrutiny as props installed on the hard!
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