Stern tube tarnish?

[diver dave]

SB?

I thought about trying the ketchup/catsup, but we haven't really stocked our boat fridges yet so didn't have any on hand. I suspect the Brasso might have been cheaper.



Did some poking around with the multi-meter, inconclusive results. I have continuity between shaft and tube, shaft and flange, tube and flange... on both sides. O Ohms resistance on the starboard shaft/tube, about 1.2 Ohms on the port shaft/tube (port being the one in question). No clue whether ~1.2 Ohms is significant, or relevant.

In our owners forum, I'm told the tube and flange are indeed separate, and the shaft is free-floating (so to speak) within the tube (i.e., supported by the gear at one end and by the two struts with cutless bearings toward the other end).

-Chris

Sorry SB = silicon bronze.
Got to be careful measuring from metal to metal when there may be galvanic voltage present. A small dmm uses ohmmeter voltage source not much stronger than the existing voltage present. If V is present, the Ohm readings will not be correct.

 

[bglad]

Conductivity of water

In this case yes. You will know better when you are on the hard. It may actually be worse than 1.2 ohms. For example, Volvo Penta Saildrives are supposed to be isolated which you can prove out of the water. But, once the system is submerged it will no longer test that way due to conductivity of the water.

We'll be hauled shortly, so I'll be able to check bonding better. I take it the ~1.2 Ohms resistance I measured between port shaft and port tube is right on the edge of significant. yes?

-Chris

 

[RT Firefly]

Greetings,
From an independent source:


WTF are those people going on about? What is the insulation resistance between 3 angels dancing on the head of a pin?



The photo shows a relatively large leak due to poor sealing between the flange, stud, and the void space behind the flange which is flooded. The moron "surveyor" completely ignored the obvious and pointed out a non issue.


The condition of the stud and its hull side threads should be determined and the flange should be resealed.


This issue has absolutely zero to do with bonding or the resistance of connections.


How on Earth did a question about something that has no impact on anything other than what should have been no more than idle curiosity turn into a sky might be falling corrosion thread?

 

[Bkay]

I seem to recall the maximum resistance between two items protected by the bonding system is 1 ohm. Seems like that's a tough standard to maintain (the source was either a Pro Boat article or something Steve D' wrote.)

Regarding:

How on Earth did a question about something that has no impact on anything other than what should have been no more than idle curiosity turn into a sky might be falling corrosion thread?

Good point. But my position is: 1) you should check bonding on a regular basis, 2) corrosion should be an easy problem to rule out and once ruled out you can focus on other solutions, 3) I've seen may small problems become big problems by ignoring evidence.

If it takes the OP a while to figure out how to perform the checks to rule it out - at the end of the process he has added a necessary skill. That's not a bad outcome either.

 

[Xsbank]

If corrosion on metal is annoying, clean it off and paint it with Le Tonkinois varnish.

 

[ranger58sb]

The photo shows a relatively large leak due to poor sealing between the flange, stud, and the void space behind the flange which is flooded.

The condition of the stud and its hull side threads should be determined and the flange should be resealed.

This issue has absolutely zero to do with bonding or the resistance of connections.

That's useful, thanks. I can't quite picture "the void space behind the flange" though; looks like solid fiberglass to me...

If it takes the OP a while to figure out how to perform the checks to rule it out - at the end of the process he has added a necessary skill. That's not a bad outcome either.

I think I'm learning... although perhaps at glacial pace.

I expect I'd understand better/faster if I had a clue what the parts (stern tube, flange, etc.) look like when they're not in a boat, but I haven't tacked that down yet.

-Chris

 

[Bkay]

I expect I'd understand better/faster if I had a clue what the parts (stern tube, flange, etc.) look like when they're not in a boat
-Chris

https://www.tidesmarine.com/shaftseals/locator.php

Don't know if the graphic on this page helps visualize it or not...

I've spent many hours climbing around the bowels of my boat and don't consider any of it a waste of time. Well, OK a little of it was a waste of time.

 

[Northern Spy]

Greetings,
From an independent source:


WTF are those people going on about? What is the insulation resistance between 3 angels dancing on the head of a pin?



The photo shows a relatively large leak due to poor sealing between the flange, stud, and the void space behind the flange which is flooded. The moron "surveyor" completely ignored the obvious and pointed out a non issue.


The condition of the stud and its hull side threads should be determined and the flange should be resealed.


This issue has absolutely zero to do with bonding or the resistance of connections.


How on Earth did a question about something that has no impact on anything other than what should have been no more than idle curiosity turn into a sky might be falling corrosion thread?

LOL. Thanks for the laugh. About time someone said something. [emoji3]

 

[diver dave]

Greetings,
From an independent source:

WTF are those people going on about? What is the insulation resistance between 3 angels dancing on the head of a pin?

I dunno; but if you can provide the test subjects, I do have the correct meter.

 

[ranger58sb]

https://www.tidesmarine.com/shaftseals/locator.php

Don't know if the graphic on this page helps visualize it or not...

I've spent many hours climbing around the bowels of my boat and don't consider any of it a waste of time. Well, OK a little of it was a waste of time.

Yeah, I had that one already... but that the shaft seal and not where the apparent leak is coming from. That said, I just got the engineering drawings for the "shaft log" (their terminology, not "stern tube") and now I've got a slightly better clue about what the thing is and how it's in there.

And FWIW, what I've been calling a "flange" is actually the internal "backing plate" -- so the tube that goes through there has it's own flange as part of the casting, but that's hidden by the backing plate that's visible in the pic.

They were also kind enough to give me a quick run-down about how to remove, inspect, reseal, replace the shaft log... so now I know maybe 1000% more than I did this morning.

A bunch of work though, and maybe an OK time to replace the Tides shaft seal, a hole bunch of hose clamps, and some hoses while I'm at it.

-Chris

 

[Bkay]

ranger42c,
I hope you don't think I've wasted your time - my apologies if you do. But if I experienced the symptoms you described (rapid change in color with no visible water leaking and in close proximity to an identical fitting that is not discoloring), I'd still want to watch closely for other signs of galvanic corrosion. That's an easy thing to do and is worth watching.

I may be more paranoid about that than some. But we are all victims of our own experience. Best of luck.

 

[ranger58sb]

ranger42c,
I hope you don't think I've wasted your time - my apologies if you do.

Not at all, thanks for your thoughts; it's made me learn something.

For anyone else who happens to have as little clue as I've started with here, I'll take the opportunity to include a pic of a shaft log (or maybe aka stern tube) that isn't exactly the same as ours but is representative of the design. What I've been calling a flange... isn't. The real flange is part of the tube casting, and it not visible inside the boat. (Duh!) The parts that are visible inside the boat are the leading end (engine/gear end) of the tube and the "backing plate".

I think I've got the engineering drawings for our actual shaft log (or at least a promising candidate), so I know about 1000% more about the whole thing than I knew before.

-Chris

 

[Bkay]

...so I know about 1000% more about the whole thing than I knew before.

-Chris

That strikes me as the attitude of someone who will be successful with complicated stuff (like boats). Hope to see you out on the Bay.

 

[ranger58sb]

We just got back from a barnacle run up and down the river... no sign of leak/drip/dampness near the port stern tube -- or anywhere else related to this.

Maybe this is all much ado about nothing... although I almost dislike it more when I have no explanation for a symptom that I've noticed... and then no repeat of the same symptom. Gremlins? I think not. But what? Dunno...

-Chris

 

[Comodave]

I would clean them up and just watch them for a while and see what happens. Good luck.

 

[ranger58sb]

Thanks, I think that's exactly what I'm going to do...

-Chris

 

[RT Firefly]

Greetings,
Mr. r. Yup. Clean up and watch. I would still plan on addressing the leak(s) on your next haul out. You won't sink any time soon but you will still seep.

 

[bglad]

Should have read down further before posting...

This might help. Same thing only three bolts instead of four.

https://www.tidesmarine.com/shaftseals/locator.php

Don't know if the graphic on this page helps visualize it or not...

I've spent many hours climbing around the bowels of my boat and don't consider any of it a waste of time. Well, OK a little of it was a waste of time.

 

[Comodave]

Greetings,
Mr. r. Yup. Clean up and watch. I would still plan on addressing the leak(s) on your next haul out. You won't sink any time soon but you will still seep.


I hate it when I seep, but it will probably happen more often as I get older...

 

[RT Firefly]

Greetings,
Mr. C. "...will probably happen more often as I get older..."

 

[Comodave]

Thanks for the suggestion, not there quite yet.

 

[bglad]

I do not think you or anyone else has wasted anyone's time here The OPs boat is in Maryland. In cold water those fittings could sweat and as a result some galvanic activity or general corrosion could occur. Fitting failure no Housekeeping nightmare yes Same as underwater fittings a protective coating would help insulate the metal from the moisture

ranger42c,
I hope you don't think I've wasted your time - my apologies if you do. But if I experienced the symptoms you described (rapid change in color with no visible water leaking and in close proximity to an identical fitting that is not discoloring), I'd still want to watch closely for other signs of galvanic corrosion. That's an easy thing to do and is worth watching.

I may be more paranoid about that than some. But we are all victims of our own experience. Best of luck.

 

[Trawler Dave]

re: verdigris

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?

If you read the article, it actually states:

These properties are all in comparison with verdigris, which is normally a duller shade, uniform across the whole of the affected object, and cannot be scratched off with wood or fingernails. Unlike bronze disease, verdigris serves to protect the metal.



I have a Marine Trader trawler, which has upwards of 800 pounds of bronze on it (bronze rudder, shaft logs, port lights, running lights, etc). No "bronze disease" there. Judging from the photo, I would call it verdigris as jleonard stated.

 

[ranger58sb]

Hah!

Following up on this... we were finally! hauled, earlier this week... NO sign of zincs wasting or anything like that. All normal, everywhere.

That doesn't solve my question about where a possible leak might have been that could have been affecting our port stern tube... I'll just have to keep an eye out for any re-occurrence of that...

-Chris