Stray marina electric currents?

[SecondBase]

Originally Posted by deblen

Folks
I may be wrong but I think the OP is telling us his depth finder bronze thru hull transducer failed,but three other "seacock" thru hulls are fine.
So,why would corrosion pick on just his depthfinder transducer??. & leave his seacocks alone?? See my earlier post for one possibility that I personally experienced on several vessels that I serviced.

Len

Good point. Question to the OP - did you have temp monitor or other likely underwater source of local current? Was this the closest thru hull to temp monitor?

[anchorman]

Originally Posted by Malbow42

Three weeks ago my 89 year old John Alden designed cutter sank in the marina. After she was refloated we found the bronze through hull transducer had failed. The threaded section through the hull had corroded somewhat but still had about 2 mm thickness, but that section had broken away. The outer flange had parted, allowing water pressure to force the rest of the fitting inside the hull. I keep an anode hanging in the water with a wire attached to the rudder post, hoping to attract any stray currents. Three other through hull fittings are in good condition.
The only conclusion we can reach is a stray current targeted the fitting & caused it to fail quite quickly.
The boat is sadly a write-off. All the internal timbers have swelled & of course the engine & electrics are gone. The boat was immersed 22 hours by the time we refloated her.
i don't know what the answer is - maybe hanging 3 or 4 anodes over the side, keeping them clean to be effective, & perhaps replacing fittings each time the boat is out of the water?

Was the fitting connected to your grounding system?

[Oceanride007]

Shame we don't know more, about bonding system and if the shore connection is isolated (if so how), or what kind of transducer. If the shore connection was not isolated thru a Transformer or Galvanic isolator and the shore earth is connected to bonding system and Transducer is bonded, well that easy to explain in a hot Marina.

Other than the transducer shorting to its (metal) body, leaking Pos DC Current will cause transducer to become Anodic, can't think of anything else.

Truly some of us like to know what happened.

Oh and in restoring a engine, much must be done when engine is removed from Salt water, immediate flushing to prevent oxidising of journals and other shiny bits. Diesel fuel pump and injectors need flushing if saltwater got in, other obvious things like Alternator good flush and drying, maybe.

I'd have waited till, Ducks were lined up, flushing out media like kero diesel would not be welcome in a Marina, FreshWater would be allowed thou, not easy and not necessary in control, I,m sorry for your loss.

[SecondBase]

Originally Posted by a64pilot

I don’t have plastic thru hulls myself, but I’m led to understand that they are hell for strong, tested to something like hundreds of lbs of pull on a side load?
From my understanding it would almost take a sledge hammer to bust one off.

Agree with a64. So to take the ABYC to task - AFAIK they bear maybe 5% responsibility for US builder corrosion sinkings due to a missing standard sending industry off in the wrong direction?

Does ABYC have a (real world) standard such that a thruhull must resist X amount of stray current for Y months?

I’m basing this on my suspicion that thruhulls fail more often from corrosion than from sideload. This, combined with ABYC not having a corrosion resistance standard (or at least not one I hear quoted) means they are perhaps addressing the second most frequent issue but not the most likely failure mode. Additionally I base this on a person almost always being present during a sideload failure (can do something about it) vs the unattended initiation pathway of corrosion failures.

Glad to be proven wrong on this one. It is possible ABYC has this right and the corrosion standard just isn’t discussed as much ...

p.s. “proper grounding system” doesn’t cut it as an excuse to me unless that vulnerable grounding system can also resist the identical sideload.

[boatpoker]

Originally Posted by SecondBase

Agree with a64. So to take the ABYC to task - AFAIK they bear maybe 5% responsibility for US builder corrosion sinkings due to a missing standard sending industry off in the wrong direction?

Does ABYC have a (real world) standard such that a thruhull must resist X amount of stray current for Y months?

I’m basing this on my suspicion that thruhulls fail more often from corrosion than from sideload. This, combined with ABYC not having a corrosion resistance standard (or at least not one I hear quoted) means they are perhaps addressing the second most frequent issue but not the most likely failure mode. Additionally I base this on a person almost always being present during a sideload failure (can do something about it) vs the unattended initiation pathway of corrosion failures.

Glad to be proven wrong on this one. It is possible ABYC has this right and the corrosion standard just isn’t discussed as much ...

p.s. “proper grounding system” doesn’t cut it as an excuse to me unless that vulnerable grounding system can also resist the identical sideload.

My guess as a Certified Corrosion Analyst with 4,586 surveys under my belt is that 98% of vessels with stray or galvanic corrosion issues are the source of their own problems. It's not an "excuse" it's simple scientific fact, a properly grounded and bonded boat as per ABYC and use of the material specifications they note will minimize corrosion.

A corrosion standard as you describe would be impossible due to the infinite number of variables.

As to plastic throughulls .... the larger sizes appear sufficiently strong but I stopped doing side load tests on anything less than 1.5" ..... I learned the hard way that they don't measure up. A Google search of "Marelon seacock failures" will give you some indication of the issue.

[SecondBase]

Originally Posted by boatpoker

My guess as a Certified Corrosion Analyst with 4,586 surveys under my belt is that 98% of vessels with stray or galvanic corrosion issues are the source of their own problems. It's not an "excuse" it's simple scientific fact, a properly grounded and bonded boat as per ABYC and use of the material specifications they note will minimize corrosion.

A corrosion standard as you describe would be impossible due to the infinite number of variables.

As to plastic throughulls .... the larger sizes appear sufficiently strong but I stopped doing side load tests on anything less than 1.5" ..... I learned the hard way that they don't measure up. A Google search of "Marelon seacock failures" will give you some indication of the issue.

Hi Boatpoker, I appreciate your humorous but all too true signature quote. Thanks for sharing your informed opinion. Any rough estimate on how many corrosion incidents you observed out of those 4500+ surveys?

[boatpoker]

Originally Posted by SecondBase

Hi Boatpoker, I appreciate your humorous but all too true signature quote. Thanks for sharing your informed opinion. Any rough estimate on how many corrosion incidents you observed out of those 4500+ surveys?

On all of them. Not being facetious, it's just a matter of degree. Corrosion starts the day the metal is made. All we can do is slow it down.

There are a few photos of what I see frequently on this page.

[boatpoker]

You might also find some useful stuff in AC DC Electrolysis ?

[SecondBase]

Originally Posted by boatpoker

On all of them. Not being facetious, it's just a matter of degree. Corrosion starts the day the metal is made. All we can do is slow it down.

There are a few photos of what I see frequently on this page.

Understood. Ok so you’ve personally observed say “way over” 2,500 corrosion incidents.

How many side load failures have you observed across this same group of boats?

[boatpoker]

Originally Posted by SecondBase

Understood. Ok so you’ve personally observed say “way over” 2,500 corrosion incidents.

How many side load failures have you observed across this same group of boats?

The answer is not as simple as you'd like. As I said, I stopped side load testing after I broke three (under 1.5") Marelon cocks very easily.

I also do not side load test any euro boat "seacocks" because none of them are ! I'm sure I could break 80% of them with little effort. All production euroboats use brass ball valves (home plumbing type) many with NPT on NPS throughulls. The installation and the crappy materials make me averse to testing them (broke a couple of those too). There is more info and photos on my website on this issue. Mainesail also has some great stuff on it.

Over the years I've probable seen 25 (?) side load breaks. In those same years I've seen 2 or 3 corroded bronze seacocks and those were probably 50 years old. In salt water one rarely sees a sound brass ball valve and if you do a search you'll find many on this forum replacing their Beneteau, Jeaneau, Dufour, Bavaria or Hanse's cheap ball valves in about five years.

A measurably corroded "bronze" (real marine seacock) is a very rare thing indeed.

[SecondBase]

Originally Posted by boatpoker

The answer is not as simple as you'd like. As I said, I stopped side load testing after I broke three (under 1.5") Marelon.

So in your experienced opinion which is a more common problem for buyers? A corrosion failure or a side load failure?

If you just aren’t sure, I understand.

[boatpoker]

Originally Posted by SecondBase

So in your experienced opinion which is a more common problem for buyers? A corrosion failure or a side load failure?

If you just aren’t sure, I understand.

If you buy a boat with proper seacocks, you have neither issue. If you buy a euro boat then you have both problems, your choice.

[SecondBase]

Originally Posted by boatpoker

If you buy a boat with proper seacocks, you have neither issue. If you buy a euro boat then you have both problems, your choice.

If you are uncomfortable with my question of which failure mode, corrosion or sideload, you have encountered more often I understand and I don’t necessarily have to have an answer.

[boatpoker]

Originally Posted by SecondBase

If you are uncomfortable with my question of which failure mode, corrosion or sideload, you have encountered more often I understand and I don’t necessarily have to have an answer.

I can see that you are a black & white kind of guy and nothing but a simplistic answer that agrees with your own prejudices will suffice. Things are more complex than you are willing to accept so good luck to you.

[SecondBase]

Originally Posted by boatpoker

I can see that you are a black & white kind of guy and nothing but a simplistic answer that agrees with your own prejudices will suffice. Things are more complex than you are willing to accept so good luck to you.

Probably - for example I can simplify the galvanic load for a new ABYC Standard. Go to ten “hot marinas” and measure current one boat slip away from the problem. Average those together and say all thruhulls need to resist that level of current for 24 months. Would that be a simple enough start?

I’m just a boat owner. I don’t hold any stock or receive any income from dealing with corrosion. Just seems like a problem you’ve seen thousands of occurrences of which could be eliminated and maybe there are competing interests IDK. Seems weird to me.

If the ABYC has no standard for resisting corrosion then they are ignoring your thousands of observations. Corrosion is just high school chemistry and easy to reproduce in a lab. WHY ignore it in favor of side load?