Shaft Zinc Mystery

[Roger Long]

Aluminum actually. I put them on myself. I've done lots. Tap with a hammer, get them tight, etc. Our boat is slow enough that I can put them about 3 inches from the struts since our shafts are light and putting them in the middle causes some vibration when they waste a bit.


They were just replaced by a diver and he thought the two on one side were missing. Then, he found them a couple feet up the shaft. How the hell did they get up there? If they were loose because I screwed up and left them loose or the area around the nuts wasted, I would think they would be down next to the strut.


Boat hasn't been out of the water since I replaced the anodes in a quick haul.

 

[Gdavid]

Did the shaft move? I could check that the prop shaft flange has a secure hold on the shaft. Obviously the shaft can only go but so far forward but perhaps it had slipped back a bit before you installed them and it shifted forward again since then.

 

[Roger Long]

Did the shaft move?

Not two feet. I think I would have noticed that like when the prop hit the rudder, the engine started racing, and water started pouring in the empty stuffing box.

 

[Gdavid]

Not two feet. I think I would have noticed that like when the prop hit the rudder, the engine started racing, and water started pouring in the empty stuffing box.

My bad, I misread and mixed up the 3" from the strut as the movement. That is a mystery.

 

[Bmarler]

They had to be loose. Either they eroded, or just weren’t tight enough to begin with. A good blast of reverse pushed them back till they got lodged in the position they’re in now.

 

[psneeld]

Very common with shaft zincs.... sometimes they corrode on the inside and become loose and weirdly screw upwards on the shafts.

More often than not, shaft zincs are the thinnest near the bolts and the screws are stainless so in aluminum they corrode even faster than zinc. Same results often with traveling up the shaft. Some guys paint around the screws to slow the depletion there and they remain in place longer.

But no matter what you do...it is still a common issue on faster boats and the worries are they slide back against cutless bearing and burn them up.

Why some go up versus down??? Never heard an airtight reason.

 

[Steve1.0]

Might be some shaft whip happening and the zincs are being "flung out" to the point of greatest rotation.? Do you have any vibration when running?