Volvo Sail Drive sudden rapid galvanic attack damage and management question

[Davidasailor26]

Conditions:
Saildrive coatings heavily compromised during "haulout" from scraping per owner photo from May 19.
Saildrive with either heavy aluminum oxide or calcium hydroxide buildup on June 3rd (inspection to determine which would be beneficial to properly diagnose the fault) per owner photo.

This is an interesting observation. It sounds to me like the saildrive wasn't damaged by corrosion itself, but by scraping the deposits off of it. That makes me lean even more toward the 12V fault being in the thruster, decaying the aluminum there, and depositing it as an oxide on the saildrive, where the current could go back into the ground circuit through the non-isolated drive leg.

 

[Charles Erwin]

PS Volvo engineers want that drive isolated. Ask them why. They will probably say we want no path for DC negative return to battery nor an AC return via the EGC (safety green) to the AC shore power source either. Engineering theory aside - follow the Volvo rules and make sure the yard does too. Don't follow the rules (or allow someone else to disobey them) and you don't get any warrantee help.

 

[boaterbob]

Not at Swantown. Interesting esoteric knowledge about Ca precipitant indicating stray current. "all fine" means testing does not indicate source of problem, yet. I hope all is fine. Will monitor closely. If saildrive was isolated per Vovo design, this would not have happened. Bought boat in Great Lakes in 2016. Perhaps term might be "reverse electroplating" to refer to removal of metal via electrolysis action. I ordered the book on corrosion. Great learning and recollection of chemistry, moles, electron flow, electrochemical potential hierarchies, circuits and problem solving critical thinking. Ultra sonic growth deterrent seems to work. Sending unit is 12 V but transducers are inside hull and one on saildrive. 20,000 to 60,000 Hertz AUDIO transmitted to hull. Not relevant unless acoustic energy removed protection from saildrive (big doubt). Will report back if cause is determined.

 

[boaterbob]

Picture of substance scraped off of saildrive. scraping of drive during first time on grid was minimal. See picure of the before and compare.

 

[boaterbob]

Bow thruster has been replaced due to short to saltwater. It was the problem. Hope Geico will se equipment failure as covered. Mystery solved in disassembly of thruster. Aloft Marine owner heard "bubbling ions" when thruster motor activated, confirming path to saltwater Great diagnostics. Boat in yard for replacement of thruster and sail drive.

 

[JamesG161]

I just found a good reference on this issue.

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Jim...

 

[dLj]

As to AC stray current - AC will degrade aluminum at about 40% the rate of equivalent DC. Other marine alloys of iron, copper, lead, etc degrade at about 1% that of DC when subject to AC stray current. (Study: Northern States Power Company (Feb 1966.) Double check there is no AC neutral (white) to safety ground (green) connection on the boat AC shore power circuit. Devices like microwave, AC/DC refrigerator, etc. may have internal neutral to ground bonding. This is a no-no in the shore power system. AC neutral to ground bonding get done at the source and the AC shore power source is on shore at the transformer.

@Charles Erwin Do you have a copy of that report? I'd love to get a copy!

Great advice above!

dj

 

[dLj]

I just found a good reference on this issue.

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Jim...

I really don't know why the marine industry - particularly the recreational marine market - refuses to use accepted terms and constantly mis-uses the term "Electrolysis"...

Electrolysis is a defined term (The NACE Corrosion Dictionary used to be easily accessed on-line but it seems to be getting harder to find. Now they want you to buy the book apparently. However, there is a copy here on SBO at Sailboat Owner's Guide to Corrosion - Basic Theories (Collier 1-4)):

Electrolysis—production of chemical changes of the electrolyte by the current flowing through an electro-chemical cell.

Electrolysis is not a term that should be used for corrosion processes - it is specific to the electrolyte found in an electro-chemical cell.

Anytime I read some "corrosion guru" using this term it is clear to me that whatever they are writing about has to be taken with a large grain of salt as they clearly don't even know basic corrosion terminology. Another blatant error in what he wrote was the 50 Hz is commercial power and 60 Hz if an American boat. Now maybe the author is in Europe where 50 Hz is primarily used. By the way, it's also used in many other parts of the world. If the author is in Europe, then the 60 Hz reference would only apply if the American boat is running a US generator that is running at 60 Hz so that would be a fairly useless measurement to make the majority of the time. That's pretty sloppy writing in any case. The OP is in the State of Washington where everything is running 60 Hz - it would be an exercise in futility performing that frequency measurement.

In any case looks like the OP found the problem in the bow thruster.

dj

 

[colemj]

I really don't know why the marine industry - particularly the recreational marine market - refuses to use accepted terms and constantly mis-uses the term "Electrolysis"...

I have the same complaint, but at least this is the first time I've seen an author clarify how they were using the term "electrolysis", as well as his implied understanding that his use of the term is incorrect.

Mark

 

[dLj]

I have the same complaint, but at least this is the first time I've seen an author clarify how they were using the term "electrolysis", as well as his implied understanding that his use of the term is incorrect.

Mark

Yeah, well at least he did try to make an explanation of how he's using an incorrect term. But there are so many red flags in that reference that I just can't swallow anything he's saying.

I especially love the "Tip: A silver half-cell is really just a piece of silver wire. You’ll find a piece at any jewelry shop in the form of silver soldering wire. Buy a 100mm piece and attach it to one multi-meter lead. Submerge the silver wire in water near the boat and measure voltage between it and the suspect metal."

Wow! Completely wrong! The silver-silver chloride half cell electrode is a silver wire with a silver chloride coating on it. This electrode is then dropped into sea water and the reaction between the silver wire and the silver chloride coating is very stable over a very wide range of saline concentrations producing a stable +0.266 in seawater (it is affected by temperature) such that by connecting your negative from your volt meter to the electrode, you then have a "reference ground plane" for the volt meter to measure the potential difference between the reaction at that electrode and the structure that you are investigating. By just using a piece of silver wire you don't have a ground plane.

Sorry - I'm having a really hard time giving that reference any credence ....

dj

 

[Charles Erwin]

Well, after all the author is a Newzeelander. Otherwise for those do not have a silver-silver chloride probe, fasten a pencil zinc to the end of the wire, get your numbers, then add -1.050. You will be plenty close enough.

 

[dLj]

Well, after all the author is a Newzeelander. Otherwise for those do not have a silver-silver chloride probe, fasten a pencil zinc to the end of the wire, get your numbers, then add -1.050. You will be plenty close enough.

That explains the 50/60 Hz... New Zealand is 50 Hz... dang Americans... Hahaha

dj

 

[Davidasailor26]

That explains the 50/60 Hz... New Zealand is 50 Hz... dang Americans... Hahaha

dj

You give him too much credit I think.

From the article - “60 hz means an American boat is leaking the current.” - An American boat plugged into shore power in NZ isn’t going to spontaneously start leaking 60 hz. If it has a fault that fault will leak at the same 50 hz as the shore power source. Maybe if the American boat is running an American inverter or generator those will emit 60 hz, but then if the boat is running an inverter or generator it probably isn’t plugged into shore power, so there’s no ground return path from your boat to theirs, and you won’t read anything when you measure voltage between the water and your ground.

 

[JamesG161]

2004 Bavaria 41 with Volvo D255 and sail drive. Problem free for 10 years of saltwater ownership.

I hope all information supplied here, helps you with your issue.
Jim...