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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 05-25-2006
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Vibration

Before launching this year I repacked the stuffing box and changed the zinc on my prop shaft. I moved the boat from the launch slip into an adjacent slip and had no noticable problems. I later moved the boat from the temporary slip into my permanent slip. All of these moves were very short distances, no more than four or five slips apart. When moving to the permanent slip the boat backed normally. In forward I experienced a slight vibration that seemed to be related to the prop shaft. When I eased into reverse there was a prounced "wobble" kind of vibration. I thought it might be that the zinc was loose or out of balance. When I installed it it wouldn't close completetly around the shaft. There was about a 1/4" gap on both sides. The yard mechanic said that was fine. If the zinc is still tight is it possible for it to unbalance the shaft or is it more likely I did something wrong when repacking the stuffing box?
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Old 05-25-2006
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If the two gaps are opposite each other and even in size, then they should balance each other out. If the gaps are opposite each other, but uneven, then the zinc will not balance properly, as it will be heavier on the half with the smaller gap.
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Old 05-25-2006
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1/4" gap seems to big

You might have the wrong size zinc (to small) and the large gap makes it possible to mount it out of true/unbalanced.
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Old 05-26-2006
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Thanks for your help.

I'm going to double check the size of the prop shaft. The Pearson manual says it's 7/8" but the 7/8" zinc really doesn't seem to fit.
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Old 05-27-2006
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If the vibration isn't the same in both forward and reverse, it doens't make sense that the problem would be with the shaft. If the problem is with the shaft (or zinc), the vibration should be the same in forward or reverse, depending only upon rpm. Since the vibration seems to differ according to the direction you're moving, the prop would seem to be the more likely cause. Is it a folding prop? When ours doesn't open evenly or fully, we get vibes. Marine growth or something caught on one blade could also be the issue. (Your post says you moved the boat to the permanent slip later, but doesn't specify if it was an hour, a few days or a week later. Stuff floats around in the current, or can grow.) Hope you don't have to haul again to fix it.
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Old 05-27-2006
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Paul makes an excellent point.. .what kind of prop do you use???
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Old 05-28-2006
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Have a check of the alignment. If You had the shaft coupling didmantled when working on the stuffing box, the alignment should be made or at least checked when back in water!
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Old 05-28-2006
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Mike,
There should be no gap between the shaft and the zinc. Either your shaft size is different or the zinc is the wrong size. Did the yard mechanic sell you the zinc? He obviously has a lack of knowlege about shaft sincs. I always tap thezinc with a hammer on both halves and re-tighten the bolts to seat it well on to the shaft. It is also possible your prop nut backed off and your prop is wobbling.
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