Need help: Bizarre Bravo III freshwater galvanic corrosion quandry

[tpenfield]

I have a thread somewhere here on iBoats that shows the gimbal ring anodes that I added.

 

[tpenfield]

Here is my thread on the gimbal anodes . . .
https://forums.iboats.com/threads/bravo-3-more-anodes.706756/

 

[rolmops]

That was my understanding as well, but it seems that different chemicals in the water, specially as the water gets warmer, tend to react with the aluminum alloy more than with the magnesium. That was the advice I was given by my local western Lake Ontario boat mechanic /small marina owner. He also claimed that close proximity to a power plant or an industrial seized power consumer throw the balance off in one way or another. High or low calcium content play a role as well. It has been a while since I played around with organic chemistry so I may be on a wild goose chase. Probably the best info available will be other boat owners and marine technicians nearby your slip.

 

[cyclops222]

We do not know what metal is used to make the thin bearing seal .

 

[cyclops222]

Very powerful underground and underwater cables also energize the surrounding waters. anchors can damage the insulation enough to charge waters.
There is so much that we do not know about areas or test for problems.
If you ever fell a tingling while swimming. STOP And swim back to where you entered the water. Save your own life.

 

[rolmops]

If you ever fell a tingling while swimming. STOP And swim back to where you entered the water. Save your own life.

Very good advice, specially the the swim back to where you entered the water part.
That way you swim a known gradual neutralising safe route back to dry land

 

[drewm3i]

That was my understanding as well, but it seems that different chemicals in the water, specially as the water gets warmer, tend to react with the aluminum alloy more than with the magnesium. That was the advice I was given by my local western Lake Ontario boat mechanic /small marina owner. He also claimed that close proximity to a power plant or an industrial seized power consumer throw the balance off in one way or another. High or low calcium content play a role as well. It has been a while since I played around with organic chemistry so I may be on a wild goose chase. Probably the best info available will be other boat owners and marine technicians nearby your slip.

I think you may be on to something here--especially since the magnesium anodes which are installed correctly are doing essentially nothing. I have thought maybe I got zinc by mistake so I will check that as well. For next season, I will go back to running aluminum anodes--they can't possibly work less either way.

 

[drewm3i]

another cause could be a incorrect charger wired incorrectly .Second place it the trim sender .With the key on there is a constant 12 volts at the sender. If the voltage is leaking from the wires you will get the same symptoms .You can rewire the system so that it only operates the gauge when the buttons are depressed

Thinking more about this, I think you are on to something. @tpenfield linked his thread where he added an anode to his gimbal ring because of similar corrosion issues. In that thread, someone also pointed out that he had broken/detached trim sender wires which would supply 12 volts with the engine on to the surrounding area (the gimbal ring). So, putting 2 and 2 together, the common denominator between the two cases is the trim sender wires dangling in the water. I am going to detach them from the engine block so they do not supply 12 volts for next season.

 

[Lou C]

Most trim senders are wired to be energized when the ignition is on, so those wires shouldn’t be getting any voltage when the ignition is off…
Even tho I’m 100% in salt water it’s not a marina where boats can be on shore power so stray current really isn’t an issue…

 

[muc]

Back in the early 2000s the dealer I worked for had a rash of these problems --- well only 8 but it seemed like a lot at the time --- so I had to learn. The first and best resource I found was from Mercury Marine, a 80 page manual part number 90-8M0167072 and it's cheap $20.00. It does a great job on the power package and boat, but not to much on stray current. ABYC had a great training guide that covered the shore power side.

What I learned from all this, was everyone was different, crazy different.
1. 23' runabout with battery charger installed like O.P. Slipped at private house. Ended up being the "invisible" dog fence 2 houses down. They had Labs so it was run out 20' into the lake.
2. 30' twin I/O in a river marina. They had grounded the CO detector to the Green wire by the main circuit panel in the cabin.
3. 48' steel hull house boat slipped at house with 2 other boats that had no problems. Customer had 2 good size ponds between house and lake, it was the underwater lighting in the ponds leaking current.
4. 32' twin inboards in small marina. Marina was "hot" and boat had been in saltwater first 2 years. Bonding wires between many components had excessive resistance.
5. 28' twin I/O small back bay. This one I swear was something called Microbial Induced Corrosion. Found the corrosion at fall haul out. It was scheduled for bottom paint so we repainted the drives at the same time. Launched in the spring and went to their house with my ref. anode, no problem found and we stored the boat for 2 years and the corrosion never came back. But the drives and gimbal housing needed a scrub and touch up every year.
6. 26' I/O marina. MerCathode went bad.

So there is no one size fits all fix. Each one is different and if your boat only has a problem at those 2 marinas, will be had to find.

Suggest you get the Mercury manual and a silver chloride reference electrode with a good DVM. Should have way less then 5 ohms between batt negative and any metal that touches water.

 

[drewm3i]

Most trim senders are wired to be energized when the ignition is on, so those wires shouldn’t be getting any voltage when the ignition is off…
Even tho I’m 100% in salt water it’s not a marina where boats can be on shore power so stray current really isn’t an issue…

Either way I have now disabled them. Seeing as the corrosion was closest to the wires, I believe this was the issue: while running, 12 volts were applied and a "battery" was created causing the electrons to flow from the open circuit into the non-conductive freshwater to the least noble metal, aluminum--aka my gimbal ring; the situation is further exacerbated by the ring's contact and proximity to the carbon steel steering pin and much stainless: hinge pins, swivel pins, etc. Due to the current, the gimbal ring thus dissolved a bit, while the steering pin rusted and the stainless pitted. The further away from the loose, dangling wires one's eyes travel, no corrosion is discernible--thus the drive itself is a-okay and well-protected by its anodes (which are barely being tested since the water's of the UP are so clean, clear, and cold).

Seriously, the water has only been ~67 and ~62 degrees, in Lakes Michigan and Superior respectively so it is not that conducive to corrosion in any way--as such, this whole thing never made much sense to me but I couldn't believe my eyes and the feel of the ring which were not deceiving me.

Also, I have confirmed my anodes are indeed magnesium and they do have small pits when viewed up close. This isn't shocking since they've been in the water only a total of nine overnights (4 and then 5).

I think this thread is solved but only time will tell. Thanks to all for your help!

 

[Scott06]

Either way I have now disabled them. Seeing as the corrosion was closest to the wires, I believe this was the issue: while running, 12 volts were applied and a "battery" was created causing the electrons to flow from the open circuit into the non-conductive freshwater to the least noble metal, aluminum--aka my gimbal ring; the situation is further exacerbated by the ring's contact and proximity to the carbon steel steering pin and much stainless: hinge pins, swivel pins, etc. Due to the current, the gimbal ring thus dissolved a bit, while the steering pin rusted and the stainless pitted. The further away from the loose, dangling wires one's eyes travel, no corrosion is discernible--thus the drive itself is a-okay and well-protected by its anodes (which are barely being tested since the water's of the UP are so clean, clear, and cold).

Seriously, the water has only been ~67 and ~62 degrees, in Lakes Michigan and Superior respectively so it is not that conducive to corrosion in any way--as such, this whole thing never made much sense to me but I couldn't believe my eyes and the feel of the ring which were not deceiving me.

Also, I have confirmed my anodes are indeed magnesium and they do have small pits when viewed up close. This isn't shocking since they've been in the water only a total of nine overnights (4 and then 5).

I think this thread is solved but only time will tell. Thanks to all for your help!

not sure where you get your magnesium annodes from, but I also had some corrosion on a fresh water alpha gen 2, Lift kept and there is no shore power to it. My hoist runs of 12 vdc. I run a revolution 4 prop which is a big chunk of SS.

I added a mercathode, still getting some bubbling around the prop hub...I had put magnesium annodes from boat zincs on it that were not sacrificing, swapped those for OEM merc ones, they do show signs of "working" and I no longer have corrosion.

I had none of this in same hoist with my old boat running aluminum props on a gen one

 

[alldodge]

In my findings aluminum is best for B3 and fresh water

Also the amount of anodes used must be done with knowing the voltage reading. Adding more anodes will change the voltage readings, so more is not necessarily better

 

[dingbat]

The "corrosion" appears to be mostly calcium scaling with a bit of corrosion here and there

In situations with dissimilar metals in contact with each other in fresh water an often overlooked and attributed to other factors is water chemistry.
Alkalinity, hardness, and pH interact to determine whether the water will produce scale, corrosion or stability of the metals.

In general, water with a low pH causes corrosion. Ideally, pH should be maintained between 7.0 to 8.5 for aluminum. 9.2 to 9.6. for steel/iron and 8.0 to 12.0 for stainless to minimize corrosion.

https://oceanacidification.noaa.gov/wp-content/uploads/2023/05/11.-Great-Lakes.pdf

Time series of pH at drinking water intakes in the western and central basins of Lake Erie illustrating short-term variability of pH


However, water with higher pH lowers the solubility of calcium carbonate making it more likely to precipitate as scale. "Whiting events" are a know phenomenon in the Great Lakes

https://www.michigan.gov/-/media/Project/Websites/egle/Documents/Programs/WRD/Inland-Lakes-and-Streams/Naturally-Occurring-Phenomenon-Whiting.pdf?rev=f6076b90b07949c3b0395c7f9308a414

Temperature speeds up corrosion however, the effect of temperature on corrosion is complex. Higher water temperature reduces the solubility of calcium carbonate which promotes scale formation and but slows corrosion. Temperature also alters the form of corrosion. Pits and tubercles tend to form in cold water while hot water promotes uniform corrosion

 

[drewm3i]

The "corrosion" appears to be mostly calcium scaling with a bit of corrosion here and there

In situations with dissimilar metals in contact with each other in fresh water an often overlooked and attributed to other factors is water chemistry.
Alkalinity, hardness, and pH interact to determine whether the water will produce scale, corrosion or stability of the metals.

In general, water with a low pH causes corrosion. Ideally, pH should be maintained between 7.0 to 8.5 for aluminum. 9.2 to 9.6. for steel/iron and 8.0 to 12.0 for stainless to minimize corrosion.

https://oceanacidification.noaa.gov/wp-content/uploads/2023/05/11.-Great-Lakes.pdf

Time series of pH at drinking water intakes in the western and central basins of Lake Erie illustrating short-term variability of pH
View attachment 411928

However, water with higher pH lowers the solubility of calcium carbonate making it more likely to precipitate as scale. "Whiting events" are a know phenomenon in the Great Lakes

https://www.michigan.gov/-/media/Project/Websites/egle/Documents/Programs/WRD/Inland-Lakes-and-Streams/Naturally-Occurring-Phenomenon-Whiting.pdf?rev=f6076b90b07949c3b0395c7f9308a414

Temperature speeds up corrosion however, the effect of temperature on corrosion is complex. Higher water temperature reduces the solubility of calcium carbonate which promotes scale formation and but slows corrosion. Temperature also alters the form of corrosion. Pits and tubercles tend to form in cold water while hot water promotes uniform corrosion

The corrosion on the gimbal ring is definitely corrosion and not pitting or scale. I believe the source to be the loose, dangling, and formerly-powered trim senders wires which are right next door (and have been since disabled).

 

[drewm3i]

In my findings aluminum is best for B3 and fresh water

Also the amount of anodes used must be done with knowing the voltage reading. Adding more anodes will change the voltage readings, so more is not necessarily better

I suppose I could go back to aluminum anodes for next season.

 

[drewm3i]

not sure where you get your magnesium annodes from, but I also had some corrosion on a fresh water alpha gen 2, Lift kept and there is no shore power to it. My hoist runs of 12 vdc. I run a revolution 4 prop which is a big chunk of SS.

I added a mercathode, still getting some bubbling around the prop hub...I had put magnesium annodes from boat zincs on it that were not sacrificing, swapped those for OEM merc ones, they do show signs of "working" and I no longer have corrosion.

I had none of this in same hoist with my old boat running aluminum props on a gen one

I do not recall if these came from Boat Zincs or Martyr (through West Marine).

 

[Scott06]

I do not recall if these came from Boat Zincs or Martyr (through West Marine).

I was surprised at how much more ‘active’ the oem ones were Vs aftermarket. Of course this is a sample size of one…funny thing is seeing ADs comment about aluminum is I took off the AL ones that were on there, PO used this boat in brackish bay areas of Deleware.

it was my understanding via word of mouth from a friend iPhone has fought corrosion issues on his B3 in upper Chesapeake, that the turning if the Ss props in the water generates current underway. Like yours his was a late 90 s vintage drive I think after his lower gear case cooroded by the bearing carrier he added a prop nut annode and a second Mercathode on his transom with two pucks vs the head under the gimbal housing. I think this worked given his marina stray electricity, but eventually his gimbal housing eroded too which was a big cost to replace

 

[cyclops222]

A bad electrical problem a distance away. Can cause that electrical battery condition to ungrounded metal parts.
Where I boat. I have no corrosion problems. NO electric on the docks or at least 1/2 mile away.

 

[JustJason]

I'm an ABYC-certified corrosion technician, and here are my two cents....

You need to get a silver/silver chloride reference cell and throw it overboard and see what you get for readings. Anything other than that is guessing at things. If your anodes are NOT corroding, that would point to electrolytic corrosion. With electrolytic corrosion, the cathode corrodes, not the anode.
With a reference cell connected to your multimeter's negative input, and the meter's positive lead connected to battery ground, you should get -800 to -1100 millivolts DC with all electrical systems off, including the mercathode.

• If you are a high, you have cathodic corrosion going on, which means that your boat may have too many anodes, the wrong type of anodes, or a boat next to yours has too many anodes or the wrong type.
• If you are low, that is galvanic corrosion, which means too few anodes, the wrong type of anodes, or a boat or structure near your boat has a lot of underwater stainless steel that your boat needs to account for.

Next, start turning on items 1 at a time and see if the reading changes. The readings should not change. If the readings change, especially a shift from - to +, there is DC stray current in the water coming from whatever is being turned on. The common offenders are trim senders, trim limits switches, faulty mercathode, and faulty bilge pump.