Need help: Bizarre Bravo III freshwater galvanic corrosion quandry

[drewm3i]

Something very odd is going on with my boat and its 7.4L/Bravo III setup that I do not understand at all. It has only started happening upon boating in the Great Lakes and plugging in at Michigan municipal (hot?!) marinas.

Here is some backstory: Soul Rebel became a freshwater boat in 2023. Before so doing, i changed all of her anodes to magnesium, including for her trim tabs. I replaced her Mercathode in 2020/21 (I forget which). I installed a basic "shorepower system" in 2022 which is basically just a plug that goes to a battery charger that I use with a 25' cord with a built-in 15 AMP GFCI breaker that I plug into the dock with a 30 amp to 15 amp adapter--I only use this to keep the battery charged and all lights, fridge, etc. are 12 volt and run off the battery.

Since 2023, she has spent about 15 overnights in various marinas plugging into dock pedestals. After getting back from our last jaunt, I noticed some serious corrosion on the gimbal ring near the steering pin that I had never noticed before (see pics). I will sand, prime, and paint it and the outdrive (as I have done before) next season, but I want to solve the issue.

Digging around the boat and bit more, I have noticed some corrosion on the engine block and steering arm (since it is bonded to the gimbal ring I imagine). The underwater stainless surfaces are also a bit pitted and some have some rust (see pictures); all underwater stainless has this white film on it. It is like the entire anode/bonding system is not working despite all of the wires being connected and intact (see pictures). The anodes are also not corroding one iota which I do not get despite them being magnesium from martyr and/or boatzincs.

I am at a loss and hope the galvanic activity has not damaged my water jackets or other internal engine water passages! Any input would be appreciated. @tpenfield @Lou C

 

[drewm3i]

I have also checked continuity between the bonding wires and there is minimal resistance (minus the paint in certain areas and surface corrosion). The real question is why are the magnesium anodes not working?

Here are some more pictures:

 

[tpenfield]

It does not look like your anodes are depleting (if they have been on for a couple of months). If they are not depleting, then they are not working. Are you using the 'star' washers to get a good electrical bond to the anodes?

The corrosion does not look too bad, except for the steering pin. Next time you have the propellers off, take a look at the main bearing carrier . . . that usually takes the worst of it in fresh/salt water.

Are there bonding wires in your boat tying all the metal components together?

FWIW, I added anodes (small clam shell type) to the gimbal rings on my Formula/Bravos, as they seemed to corrode the worst of anything.

 

[Grub54891]

Did it previously live in saltwater?

 

[alldodge]

If your boat is well grounded and the marina or boat next to you is not, it all heads your way

Only way to know what the problem is, is to measure the voltages while sitting in the water for 24 hours with the correct probe and digital meter.

Adding more anodes can cause more issues than solving the problem. Need to have voltage reading between 620 - 1180 mV for fresh water

 

[Bt Doctur]

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

 

[Lou C]

There are ways of measuring if you have enough anode protection; and I agree your’s don’t look depleted as one would expect. When I pull my boat after 6 months on the salt water mooring they’re about 20 % depleted, I always put new ones on in the spring.

 

[cyclops222]

I do not lke the corrosion of .....SOME..... of the bolts in a group. Looks like ...Plain ....old salty corrosion. Or even salty spray on the motor.

Still need to check the marina / dock power outlets for correct grounds.

 

[Lou C]

Corrosion Reference Electrode with User's Guide | BoatZincs.com

Corrosion Reference Electrode with User's Guide | BoatZincs.com | America's Superstore for Marine Anodes

boatzincs.com

Check this out, this is a way of measuring if you have enough protection…

 

[cyclops222]

I read the description on the website. Can not form a opinion about it from instructions given.

 

[drewm3i]

It does not look like your anodes are depleting (if they have been on for a couple of months). If they are not depleting, then they are not working. Are you using the 'star' washers to get a good electrical bond to the anodes?

The corrosion does not look too bad, except for the steering pin. Next time you have the propellers off, take a look at the main bearing carrier . . . that usually takes the worst of it in fresh/salt water.

Are there bonding wires in your boat tying all the metal components together?

FWIW, I added anodes (small clam shell type) to the gimbal rings on my Formula/Bravos, as they seemed to corrode the worst of anything.

The anodes are not depleting and I have no idea why--maybe a residual aluminum oxide barrier?; maybe the packaging was wrong and I got zinc anodes? It looks like the metal is "passivated" for what it's worth. I replaced the existing aluminum ones with magnesium in 2024 (did not splash in 2024) and since putting it in and plugging in to shore power at marinas on the Great Lakes, have seen a lot of this pitting and full-scale corrosion of the gimbal ring. What's weird is the magnesium anodes on the trim tabs are also not really corroding either. The prop anode is aluminum (that's all they sell for the original Bravo III prop nut).

The main bearing carrier was fine when I had the props off last. I had previously painted it and I always slather it with grease when off. I seal/protect the steering pin with grease as well, but that has worn off after numerous trips this year.

The bonding wires are indeed in place and intact--I tested continuity between wires and there was some resistance but no open circuit. I am also using the star washers which are needed to cut through the metals to create a good electrical bond. Really everything is done right to my eye so I am at a loss; hence the suspicion of stray current.

I may have to add anodes to the gimbal ring--thanks for the great idea Ted! Where did you add them? As it stands, the gimbal ring is bonded to the bell housing via wire and to the drive via the mounting bolts. Still, this doesn't seem to be protecting it.

 

[drewm3i]

If your boat is well grounded and the marina or boat next to you is not, it all heads your way

Only way to know what the problem is, is to measure the voltages while sitting in the water for 24 hours with the correct probe and digital meter.

Adding more anodes can cause more issues than solving the problem. Need to have voltage reading between 620 - 1180 mV for fresh water

What's weird is it is very clear my gimbal ring is acting as the anode for my boat, while the actual magnesium anodes are doing nothing.

 

[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

Yes the trim sender could be an issue when running. I will cap those (very corroded) wires.

The charger though is 100% not wired incorrectly. It is simply plug and play to the dock with terminals to each of the two batteries. It is a Pro Mariner 20 Amp Dual Bank marine smart charger so it is ignition protected and has many integral safety features. In fact, it doesn't work with sketchy extension cords due to detecting a fault.

 

[drewm3i]

I do not lke the corrosion of .....SOME..... of the bolts in a group. Looks like ...Plain ....old salty corrosion. Or even salty spray on the motor.

Still need to check the marina / dock power outlets for correct grounds.

Did it previously live in saltwater?

No salt here--in fact in saltwater, stray current is much less destructive because of the conductivity of the water itself.

She was run on brackish<fresh water on the Upper Chesapeake for a few seasons, but since 2023 has been on the Great Lakes. There was no corrosion of the bolts, trim lines, or gimbal ring (minus the steering pin which I always paint/grease in a never-ending battle) until very recently when we spent 9 nights at two different Michigan municipal marinas plugged in. In fact, after getting back I just noticed it and I am always keeping tabs on things.

 

[cyclops222]

Those 2 marinas could be wired incorrectly. Have the marinas do a electrical test of the 120 / 240 VAC outlets to the water around the boat. T he water may be at 120 vac and electrocute a swimmer. It has happened and caused deaths.

 

[alldodge]

Those 2 marinas could be wired incorrectly. Have the marinas do a electrical test of the 120 / 240 VAC outlets to the water around the boat. T he water may be at 120 vac and electrocute a swimmer. It has happened and caused deaths.

Never found a Marina that allows swimming off the dock. Also have never heard of a Marina do any testing unless the State requires it

 

[cyclops222]

Years ago 2 young girls jumped from boat into water to cool off. 1 drowned from electric current flowing in the water.

 

[drewm3i]

Those 2 marinas could be wired incorrectly. Have the marinas do a electrical test of the 120 / 240 VAC outlets to the water around the boat. T he water may be at 120 vac and electrocute a swimmer. It has happened and caused deaths.

It totally could be wired incorrectly. In fact, I would expect state marinas with no competition or incentive to be good to be wired as such.

 

[rolmops]

It seems that aluminum indium alloy anodes work better in the great lakes, specially during the warm summer months

 

[drewm3i]

It seems that aluminum indium alloy anodes work better in the great lakes, specially during the warm summer months

My understanding of this chart is that the more active anode (magnesium) should protect better in pure freshwater like the Great Lakes (Lake Michigan and Superior)? Even the one aluminum anode on the prop shaft also isn't corroding!