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Old 05-12-2019, 08:29 AM   #1
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Stern tube tarnish?

The other day, I noticed what seemed to me to be more green tarnish than usual on our port side stern tube... much more than what's on the starboard side tube.

I haven't found any source of water on these... other than plain old general humidity in the engine room.

My first thought was that maybe the Tides SureSeal dripless shaft seal on that side might be going south, but the hose clamps there are good and tight, there's no sign of leakage, and any dripping would be at the other end of the blue "articulated hose" anyway.

Thoughts?

What's a good bronze cleaner?

-Chris
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Old 05-12-2019, 09:01 AM   #2
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Greetings,
Mr. r. Might be one of your stern tubes was "cleaner" (less oily/greasy) than the other and the humid ER conditions generated the verdigris. Not necessarily a leak but worth monitoring. I'm looking for a good bronze cleaner as well. Preferably spray/brush on and hose off...


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Old 05-12-2019, 12:38 PM   #3
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Verdigris! Exactly. Hadn't remembered the word...

I would have thought both tubes would have been in the same general condition before all this, but actually it must be that I wasn't noticing any recent changes.

There's much more of it on the port tube, and that's even after wiping some of it off with a dry rag. In fact, I also cleaned up (also with a dry rag) a bunch of the stuff from the hull area directly below; there's are a couple of signs of that still remaining in the pic. It's like the stuff was wet and actually dripping off that tube.

No signs of actual moisture though, even when I was down there while we were underway on this last Friday. No sign of water leakage anywhere near the stern tube, shaft, seal, etc. We do get a little sea water in there from time to time, near as I can tell from spray (and sometimes "sideways" rain) into the engine room vents on the sides of the hull. Nothing directly on the tubes though...

The starboard tube is normal, as shown here au natural with no cleaning at all at least within the last 14 years.

-Chris
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Old 05-12-2019, 04:16 PM   #4
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Looks like leak/corrosion staining on these two bolts.
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Old 05-12-2019, 10:49 PM   #5
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Looks like leak/corrosion staining on these two bolts.
I'd replace the rusted hose clamps with better quality.
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Old 05-13-2019, 07:13 AM   #6
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Its that natural protection layer for the bronze. I would not worry about. Just keep an eye on it.
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Old 05-13-2019, 07:39 AM   #7
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Greetings,
Mr. jl. Somehow I don't think the verdigris is "natural" protection for bronze in the same fashion that aluminum oxide protects aluminum if you can understand what I'm attempting to say.


"If not treated, complete destruction of the affected artifact is possible..." Taken from this article:


https://en.wikipedia.org/wiki/Bronze_disease


I'd clean it off and apply a light coating of oil/grease. That still begs the OP's question. What's best to clean it off?
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Old 05-13-2019, 08:02 AM   #8
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Quote:
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Looks like leak/corrosion staining on these two bolts.
Hmmm... hadn't thought of a leak there. I'll check, thanks.


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I'd replace the rusted hose clamps with better quality.
Yeah, they're a little unsightly. They're ABA clamps, though.


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Greetings,
I'd clean it off and apply a light coating of oil/grease. That still begs the OP's question. What's best to clean it off?
A dock neighbor suggested Corrosion-X, Scotch Brite pads, and a brass wire brush. I assume that means "elbow grease" as well.

OTOH, it looks to me like Corrosion-X is meant as a retardant (like Boeshield or similar), not specifically as a cleaner.

??

-Chris
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Old 05-13-2019, 09:26 AM   #9
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Greetings,
Mr. r. Yes. I always thought of Corrosion-X and similar as retardants as well. I found this on line:


General Purpose Bronze Cleaner: Salt, Vinegar, and Flour. Dissolve 1 teaspoon salt in 1 cup white vinegar. Add enough flour to make a paste. Apply paste to bronze and let sit for 15 minutes to 1 hour. Rinse with clean, warm water, and polish dry.


Seems counter intuitive to use salt where salt was the causal agent in the first place but...


In a former life I used Nitric Acid in various concentrations to remove the oxides from copper, brass and bronze. Did a GREAT job but MUST be done in a fume hood (laboratory). Nitric Acid is NOT, I repeat NOT a chemical to be used unless under VERY controlled conditions.


EDIT: It has just been pointed out to me by a knowledgeable and anonymous contact that there is an obvious track of verdigris from the port upper inboard mounting stud signifying a LEAK. I suggest that the fitting (shaft log perhaps?) be re-bedded to eliminate same. How did our surveyor miss that one? Perhaps it was SO obvious that it didn't bear mentioning. (that's what I thought anyway...).
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Old 05-13-2019, 10:05 AM   #10
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Greetings,
General Purpose Bronze Cleaner: Salt, Vinegar, and Flour. Dissolve 1 teaspoon salt in 1 cup white vinegar. Add enough flour to make a paste. Apply paste to bronze and let sit for 15 minutes to 1 hour. Rinse with clean, warm water, and polish dry.

EDIT: It has just been pointed out to me by a knowledgeable and anonymous contact that there is an obvious track of verdigris from the port upper inboard mounting stud signifying a LEAK. I suggest that the fitting (shaft log perhaps?) be re-bedded to eliminate same. How did our surveyor miss that one? Perhaps it was SO obvious that it didn't bear mentioning. (that's what I thought anyway...).

I think I've got some oxalic acid jelly (forget the brand name) on board somewhere, and I was thinking about trying that... Seems like the definition of verdigris suggests an acidic clean-up solution. I think. Maybe.

Boatpoker's post #4 also points to a possible leak there, and I'll be checking those studs specifically. I can't quite picture how a slow leak there would crawl up the stern tube toward the shaft seal, though. I was watching, the other day while we were trolling, and didn't see any sign of water ingress anywhere around there -- but we were trolling at very slow speeds, with the shaft hardly turning, so it may be that leakage only occurs at higher speeds. Maybe.

I'm a little unclear about terminology. Is the stern tube bolted to the "shaft log"? Or does that big hunk of fiberglass even have a name?

-Chris
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Old 05-13-2019, 10:13 AM   #11
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Greetings,
Mr. r. I'm unclear on the terminology as well. What I'm suggesting be re-bedded is the flange the 4 studs/bolts pass through. So, take the 4 nuts off and if possible, separate the flange from the big hunk of fiberglass and apply the sealant of your choice between the flange and the hunk. I have no idea IF it will be this simple but there IS a leak around that stud.
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Old 05-14-2019, 06:47 AM   #12
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Thanks; yes, I understood what you meant about re-bedding.

I'm awaiting additional guidance from an expert in the business with our brand of boat.

Happens we're due for our annual haul-out (powerwash, check-up, anodes, wash/wax, etc.) so it may be possible to combine stern tube work into all that at the same time. If so, I'm thinking I might as well replace the shaft seal, maybe some new hoses and clamps... and might as well do (almost) all of that on the other side, too.

-Chris
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Old 05-14-2019, 07:56 AM   #13
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I was watching, the other day while we were trolling
You know it is a bad spring rockfish season when you return to the dock having completed a full mechanical survey, organized your galley utensils, optimized your AIS and DSC. Oh, and you also had time to schedule your real ID appointment at the MVA.
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Old 05-14-2019, 08:23 AM   #14
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I freely admit that I don't know much about much - so take my comments with that in mind. First, I have a lot of experience with bronze and the natural verdigris is not a big concern to me on it's own. But I'd me more concerned about why there is an uneven tarnishing between port and starboard.

I would at least check the prop shaft anodes to see if they are eroding at a similar rate. I would also consider checking if there is electrical connectivity between the shaft and stern tube. I believe the Tides SureSeal should keep those two metals separated, but I would confirm that since it's an easy thing to check.
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Old 05-14-2019, 08:36 AM   #15
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You know it is a bad spring rockfish season when you return to the dock having completed a full mechanical survey, organized your galley utensils, optimized your AIS and DSC. Oh, and you also had time to schedule your real ID appointment at the MVA.
Yeah, that pretty much captures this year's session... <sigh>...


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I freely admit that I don't know much about much - so take my comments with that in mind. First, I have a lot of experience with bronze and the natural verdigris is not a big concern to me on it's own. But I'd me more concerned about why there is an uneven tarnishing between port and starboard.

I would at least check the prop shaft anodes to see if they are eroding at a similar rate. I would also consider checking if there is electrical connectivity between the shaft and stern tube. I believe the Tides SureSeal should keep those two metals separated, but I would confirm that since it's an easy thing to check.
Thank you; I've been wondering if someone might suggest a bonding or electrolysis issue, given the disparity. Some local circumstances in the marina could be involved, with some nearby changes over the last year or so... Anyway, when we haul soon, I'll certainly be checking anodes and especially on that side of the boat.

In the meantime... I don't actually have a clue how to check for stuff like that -- including shaft versus stern tube, etc -- from inside the boat. Multi-meter? What settings? Where to probe? What voltages to expect (or not)? What's good, what's bad?

-Chris
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Old 05-14-2019, 09:36 AM   #16
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I usually hurt myself with a volt meter, so I'm not the best source. But in this case, it should be painless to start trouble shooting.

I'd start my looking at the resistance (ohm setting) and see if there is any electric connectivity between the shaft and the stern tube. If you have infinite resistance then there is no connection. It should be the same on both shafts. (note: Touch the probes to two different, unconnected pieces of metal to see what infinite resistance looks like. Touch them to each other to see what 0 resistance looks like.)

If there is good connectivity between the bronze stern tube and the shaft and both read similar, then checking for even wear in anodes is simply a matter of looking at them when you haul.

You may find no connectivity (infinite resistance). If there are any readings that are different from one side to another or if there is materially different wear in the anodes, I'd ask a smart electrician to assist with a survey. I have always seen those done in the water with a silver/silver chloride reference anode hung over the side and readings taking from inside the boat to determine the difference in potential. This is something that you are better off watching the first time.

With a haul out coming, I'd be satisfied with just confirming whether either or both sides have continuity. If they do, then your shaft anode is the protection for the stern tube. If everything looks and feels normal, then you are probably back to the question of how to clean up the verdigris. But if copper bottom paint is turning colors around the fittings, an anode is worn through, or one side has a difference in continuity, then it's time to talk to a smart guy.

Hope that helps. I usually just try to common sense these things out until I get frustrated then hand someone a bag of money to explain what the clues mean. Hopefully someone better educated than me will chime in.
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Old 05-14-2019, 01:14 PM   #17
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Thanks, it does help.

To clarify one point: I DO (0 resistance) or DO NOT (infinite resistance) want connectivity between shaft and tube?

I kinda thought the shaft wouldn't actually be touching the tube, but then I don't know what the inside of all that looks like...

The flange around the tube is bonded (green wire)... but now that I've cleaned it up a little, it's looking more and more like the tube and the flange are separate pieces... and if so, the tube isn't connected to that green wire... I think...

For RT ref cleaning: a search on "bronze cleaner" turned up those household cleaners, paste of flour/salt/vinegar, lemon juice, etc that you mentioned... but it also turned up Brasso (says also for bronze) and a 3M Metal Restorer and Polish (says also for bronze), along with some other commercial products.

Brasso ($5.59 at the local grocery) seems to be working OK, with the aid of a small brass wire brush and rags and so forth. I'm prepared to try the 3M product if necessary ($27.99 from Amazon, manana... or $44.xx from the local West Marine) but that may not be necessary.

In my case, cleaning is maybe turning into more of an access issue than a product issue. I can only reach that port side tube with a wire brush in one hand with arm extended... and there's an engine exhaust and a Racor in the way so I can't always see what I'd doing either... Half hour job on the bench, probably 3 hours job in the boat. Not uncommon.

-Chris
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Old 05-14-2019, 02:05 PM   #18
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Greetings,
Mr. r. Yes. Quite familiar with Brasso. Good stuff for brass and copper alloys. Also good for polishing headlight lenses/plastics due to it's mild abrasive qualities. Cleaning of oxidized surfaces is effected more by mechanical means (rubbing) than by chemical means although there IS some chemical removal of oxides.


I looked up the MSDS for Brasso and it contains, as I suspected from the smell, amonia as well as oxalic acid.


ammonia 5 - 10%
Oxalic acid, dihydrate 1 - 2.5%
Isopropyl alcohol 1 - 2.5%


I may have to haul out my Junior Woodchuck Chemistry kit and make up my own cleaner at some point. I DO agree with you that it is a LOT easier working on a bench than doing "Pretzel Yoga" on a boat.
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Old 05-14-2019, 02:13 PM   #19
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Thanks, it does help.

To clarify one point: I DO (0 resistance) or DO NOT (infinite resistance) want connectivity between shaft and tube?
How am I supposed to know that? Just kidding - but not really.

I'm not sure how you are set up, I would assume that you would want no connection between the tube and the shaft. That's the way my last two boats have been. But I suppose it is conceivable that you are designed to have contact. My suggestion for figuring this out is to determine whether there is contact or not because these are clues you will discuss with an electrician if it starts looking like some type of galvanic corrosion is occurring. If there is infinite resistance (i.e. no contact) and your anodes look similar, then you can be somewhat assured your shaft is not consuming the tube.

Having said that, you mentioned a green bonding wire, that tells me you have a bonding system and the stern tube is attached to a hull zinc somewhere. There is a different test to determine if this fitting is still being protected by the bonding system. But I don't type fast enough to address it.

If this is an older boat and you have never checked your bonding system, that might be a good thing to do at the yard as well since they are prone to failure over the years.
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Old 05-14-2019, 02:17 PM   #20
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Now that I think about it, you can check the continuity of the two stern tubes. If they have good continuity, then at least those two items are connected (even if they are not connected to the rest of the bonding system). If they are connected, they should be corroding at similar rates. If there is no connection, get help trouble shooting your bonding system.

If you find good continuity and no other sign of galvanic corrosion - I might not loose any sleep over the fact that one is tarnishing and the other is not.
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