Reference Cell Test Results, Help to Determin Resolution

[boatbod]

There are numerous issues, not least of which the bellows weaken over time and have to be replaced every 5yrs, give or take.

Once a leak starts, be it caused by poor alignment or weak bellows, the stainless rotor pits and gets totally gummed up with salt deposits and other junk.

Considerable maintenance required, and replacing bellows requires a shaft pull.

Also very easy to get the bellows installed off-center on the shaft log just by tightening the house clamps.

[groundtackle]

Boatbod, your comments are valid but can be remidied. I'm not a pss salesman but my clients read this thread. I'd like them to feel confident.
* bellows weakens. Yes it does. I try for 2 1/2-3 yrs between haulouts. I change the bellows every other haulout. 5-6 yrs. I think thats ok. The kits are a little pricy but im ok with it, for its special perpose in life.
* 5-6 yrs also Change the o-rings, all the set screws and have a good look at it all. Throw the ss rotor on the lathe and give both sides a good polish or skim. Sometimes I just flip them so 10-12 years before another skim or machine.
* they do get ugly on the outside with gummy salty debris. When I get them apart those surfaces are usually spotless. I stopped cleaning the outside other than a qwick scotchbrite, just for looks.
* pulling the shaft. my feeling is the shaft should come out of the coupling every 5-6 yrs anyway. You get a chance to inspect all those spinny things, rear seal, rusty bolts, key slop and alignment etc. Not sure why a seal leak can be blamed when you have a missalignment issue.
* stern tube. I agree they can get off centre when tightening. The bellows material is soft and all i use are awab's so you can squish the guts out of them if you overtighten. If the tube is rough glass or off centre then yes, thats an issue that needs to be addressed first. Take some care when setting the bellows, try a few posititions before deciding to say its good enough.
I don't feel them to be considerable maintenance at all, just maintenance. What seal do you prefer?
ce

[RaymondR]

Originally Posted by senormechanico

It's not a resistance reading, but after electrically coupling mine as above, I got exactly the same voltage reading on my bonding system to the reference cell.
I measured the prop shaft, the bonding system in the middle of the boat, and at the forwardmost thruhull.

AFAIK, it's working fine.

So it appears that for all practical purposes there is no voltage difference between any of the submerged metal components to drive any current flows and consequently should not be any electrolytic corrosion. The bonding is complete and effective.

[boatbod]

Groundtackle,

I think we're in agreement that 5-6 years is about max bellows life and also time to perform major overhaul of rotor & o-rings. On a twin engine 40 footer, you're looking at a $2k repair bill, which although not excessive, is not exactly peanuts either.

Loss of other options out there, and much to be said for regular packing glands. We've tried most everything at some time or other and all have pluses and minuses.

[senormechanico]

Originally Posted by RaymondR

So it appears that for all practical purposes there is no voltage difference between any of the submerged metal components to drive any current flows and consequently should not be any electrolytic corrosion. The bonding is complete and effective.

Yuppers, with the exception of the zinc itself.