Rapid zinc deterioration with PSS shaft seal?

[WillieC]

I have the A25 with original SS shaft and bronze prop. A PSS shaft seal has been installed replacing the original stuffing box. The PSS shaft seal utilizes a black carbon or graphite ring, not exactly sure. And I have fairly rapid zinc failure on the prop shaft. The shaft is electrically isolated from the engine by way of flexible shaft saver.

We have a private mooring ball out in the Canal we use only during boating season, and haul out over winter. We often pull it out during the season having a private boat launch and custom trailer. It rarely sees a marina. The electrical system is bare bones, modestly improved original, the most sophisticated add-on being an echo charger and higher capacity alternator with isolated ground.

I have been following the discussion here Stern Glands:

viewtopic.php?f=20&t=9719

and don't want to hijack that thread.

Nepidae mentioned Steve D'Antonio's comment about carbon and SS making the SS the sacrificial metal! Yikes!
http://www.trawlerforum.com/forums/s31/ ... 057-3.html

I can change zincs monthly if I need to but it seems odd. And I certainly want to sort this out before reworking the shaft and prop. Others have weighed in that I must have some serious leakage issues, but with an isolated shaft and simple electrics and brackish water I am somewhat stumped.


Could the PSS seal be causing my rapid zinc failure?

[Tree]

I would think that since the shaft is isolated from the system that's the first route of the problem. You can buy shaft brushes that mount in the shaft allowing them to be in contact with the rest of the boat zincs. It could also be possible you have someone near your berth with a bad setup that could lead to eating away yours and others zincs. This is where galvanic isolators are worth their weight in gold. A commercial fisherman friend of mine had one of his propellers destroyed on his catamaran a while back, that was found to be caused by a new berth holder with a bad setup. Both boats were plugged into the electric hook ups on the pontoon and the rest is history!

[WillieC]

1. The only other boat zincs are, a: on the SS rudder support shaft, fairly close to the prop shaft. and b: pencil zincs in the heat exchanger. There is no other metal in contact with seawater, save for a few through hulls that immediately convert to non-metallic hoses.

2. "We have a private mooring ball out in the Canal we use only during boating season, and haul out over winter. We often pull it out during the season having a private boat launch and custom trailer. It rarely sees a marina." The nearest boat on a ball is a few hundred feet away. There is no shore power out in the middle of the canal.

What is the purpose of making the shaft and engine electrically continuous? The only electrical connection from the engine to the seawater (with my isolated prop shaft as is) would have to be only through the seawater flowing through the heat exchanger and out the exhaust. (There might also be an electrical connection through the rudder shaft and its cable to the steering wheel. I am unaware of any electrical connection between the steering wheel and the control levers for throttle and transmission. I have not tested that circuit with an ohmmeter.) What am I missing? I could easily connect the engine to the shaft with a couple of copper bonding straps at the shaftsaver coupling. Seems to me making that connection would make the whole engine susceptible to galvanic corrosion.

Do I need to electrically tie the rudder support shaft to the prop shaft? Any A25s out there with this set up? Or should I remove the zinc on the rudder support shaft. I have seen other A25s set up like that.

[Nepidae]

Willie,

I think I would look in the area of stray current.

Steve D'Antonio comment was in reference to possible pitting of the shaft where the graphite packing is, due to dissimilar metals, your current issue sounds much worse. I'd also offer that your isolated shaft is not getting the benefit of your grounded boat, so I would look in the water around you and since you have a private dock, I'd start there with a qualified electrician checking out your dock. THIS IS NOT the type of work that a regular home electrician is qualified to do.

I would also agree that a galvanic isolator would be a step in the right direction. This will help with stray current, AGAIN, not the job for a home electrician. Get an ABYC certified electrician and have it done right.

You are lucky, this is a warning of an issue and the loss of some anodes is a small price to pay, but it could get worse. I wouldn't put off attending to this matter ASAP.

Good luck.

[Cape Codder]

My suggestion is to STOP using any copper-based anti-fouling paint!
Use Pettit Vivid or better yet, Pettit Hydrocoat Eco to minimize electrolysis, and or current.
They are BOTH copper-free, and perform top notch.

[WillieC]

Now that may be a good suggestion. Thank you, Cape Codder. Mine is ablative, red in color, and ready for replacement, likely copper based since it is old. Hydrocoat Eco is top of my list.

[Northern Spy]

Are you using the right anode composition? I use zinc in brackish with occasional trips to salt water. I have a PSS seal on factory SS shaft with a bronze wheel. The only difference with my setup is I don't have a flex coupler. I am berthed in a marina with suspect boats and wiring every where, and I stay plugged in to shore power. A single anode lasts me a year. My heat exchanger eats the pencil anodes up though.

[DougSea]

I found some good information on another forum - see here: http://www.cruisersforum.com/forums/f14 ... -1362.html

If it were my boat I'd put a brush on the shaft and bond it. Bonding allows current to flow between the metal fittings on your boat without flowing through the water - and reducing your corrosion. You still need a zinc on the shaft to protect the dissimilar prop and shaft.

[WillieC]

Anodes are zinc, I am in saltwater. Doug, thanks for the great link. Don't have time right now to read it all.
Now that the engine is out of the boat, I will be removing fuel tank and batts and do some major cleaning. Also, while boat is much lighter, I will be doing bottom paint

Thanks all for the advice!