Vibration

[mtbmike]

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?

[RichH]

A shaft zince must be very tight on the shaft. If there is any 'looseness' the zinc will spin (precess) on the shaft and 'may' cause the slight 'wobble' that you are noticing.

[sailingdog]

Also, if the zinc isn't completely tight against the shaft, it will not perform its primary function—protecting the shaft from galvanic corrosion—very well.

[LaLeLu]

Did you check your cutless? Perhaps your bearing is going out.

[Fstbttms]

Originally Posted by mtbmike

There was about a 1/4" gap on both sides. The yard mechanic said that was fine.

Time to find a new mechanic.

My bet is that the zinc came loose. Clearly it was not installed properly or was the wrong size to begin with. In the future, seating the zinc on the shaft with a few well-placed hammer blows will help insure not only a snug fit but good electrical contact as well. Have a diver check and replace (if necessary) that zinc you have on there now.

[seamountie]

What ever it is it appears to be progressive, and reasonably quickly progressive. I do not know if you experienced the wobble or vibration for long, but did you notice if the vibration was steady or was is cyclical. If there was any hint of it being cyclical, I would check the prop as well as the zinc.