Galvanic Isolators

[Caliente]

At the urging of "Wahoonbox" , I am posting on this forum on a topic some of us know too well... Electrolysis. I had responded to a fellow member who keeps his boat in the same marina as mine. He related that an electrical problem with the transformer serving the facility was eating up his lower unit.

I informed him that I had a similar problem (not as severe) on my own boat. Mine is an inboard and I had noticed pitting of my props when it was out last year. The prop shop confirmed that electrolysis was the cause.

I then decided to do some research.Aside from the normal theory of dissimilar metals in salt water causing the "battery effect" and causing low currents to errode zincs I also found out that boats connected to shore power circuits can cause an additional problem.Stray low voltage currents flowing between the AC ground wire and the boat's DC bonding system will create a "galvanic " action. This type of stray current will overload your zincs.

I then purchased and installed a "galvanic Isolator". Its job is to block a majority of the low voltage currents. It is installed in series with the shore tie ground wire and should keep my zincs from dissapearing so fast.

Anyone who is interested can "Google" Galvanic Isolators and find about a dozen brands (I bought one from Newmar) as well as discriptions and discussions on the topic.

[Reveille75]

I have galvanic isolators on my shorepower system to prevent excessive damage to my zincs. I can't prove it but I think if you have a neighbor who is creating the aforementioned low voltage stray current, he can eat up your zincs. The zinc eating got so bad in our harbor we had it checked. Turns out we have a1/2 volt of current running through the water at all times.I keep my boat in a lift but my neighbor lost every zinc on his boat in less than a month after a haul. It seems like this is something that could be traced or countered in some way. Does anybody have any experience in this area. I am so electrically challenged I believe that removing a light bulb lets electricity fall on the floor so be gentle with your sharing.
David

[LuckyLady]

There are so many things that cause galvanic corrosion.

Mercruiser discovered a major problem with the older bravo III stern drives back in early 2000 where customers were pulling there boats out and if you touched the skeg it would crumble in your hand.

One of the main causes of that was that with it was dissimilar metals was that they found out when bottom painting bottoms the paint was going all the way up the to the transom assembly there for causing the dissimilar metals between the paint and the drive.

In order to avoid the above problem you need to leave a 1" gap between the bottom paint all the way around the entire outboard bracket or transom assembly.

Another couple things that I have seen happen is electric trim tab cylinders some times fail and explode the case and allows water in there for putting stray current in to the water.

Another problem I have seen is with bilge pumps/float switches sometimes the wire breaks or the connection is actually sitting in the bilge water causing stray current.

Then the ever so common culprit is other boats surrounding you or shore power cords.

The last time I had an issue they almost indicated that if you are an outboard and surrounded by stern drives you are more susceptible to it. Not sure the truth of this but most stern drives here are dukey crusiers.

The document attached is a great tool and put understanding to how it happens

Hope this helps

[Reveille75]

Mary:
Is there a device that will absorb stray current from surrounding boats or protect a slip? I expect my problem is originating from another boat.
That was a great walk thru on galvanic corrosion, I think I got it.
David

[LuckyLady]

Mary:
Is there a device that will absorb stray current from surrounding boats or protect a slip? I expect my problem is originating from another boat.
That was a great walk thru on galvanic corrosion, I think I got it.
David

Not to my knowledge, about the only thing you an do is give it something else to eat, they make zincs that you can hang off the side of your boat or the dock. But I do not think there is a enough zincs in the world to stop another boat, but its worth a shot. I think they are like 30 bucks each and I think if its bad you will be paying 1000s of dollars

What is getting eatten up?

What kind of boat? Engines?

Most manufacturers having bonding systems in place for trim tabs, brackets etc - If there is a break it in somewhere it will cause you problems too.

[OffTheHookB&T]

We had a crazy electrolysis situation happen at the marina years ago.
Early one morning, one of our staff came running into the office and said that we had a boat sinking. We went about the usual procedures, but we couldn't get a hold of the owner and he had never left the office a set of keys We tried to pump it but the water was in the bow and had no keys for the cabin, so we decided to tow it to the travellift and pull it.
Well when the boat was high enough I reached under to remove the plug and the plug and fitting looked like they had been dipped in acid Also, there was water pouring from where the bottom mounted transducer had been As I stepped back I noticed the outboard bracket was eaten away as well, it looked like white coral. But the zincs we're fine The crazy thing was the owner had just used the boat a week before.
After checking the docks for bad wires and the other boats on the dock we were baffeled.??
When we checked the boat we found a hot wire was connected directly to the bonding system
Turns out the someone in the owners family had replaced the batteries and decided to FIX some wiring problems
The electrolosis was so bad on this boat, mechanics from all over the local area came to take a look at the damage, most of them couldn't believe it. If I can find the pics I'll post them later.

[LuckyLady]

We had a crazy electrolysis situation happen at the marina years ago.
Early one morning, one of our staff came running into the office and said that we had a boat sinking. We went about the usual procedures, but we couldn't get a hold of the owner and he had never left the office a set of keys We tried to pump it but the water was in the bow and had no keys for the cabin, so we decided to tow it to the travellift and pull it.
Well when the boat was high enough I reached under to remove the plug and the plug and fitting looked like they had been dipped in acid Also, there was water pouring from where the bottom mounted transducer had been As I stepped back I noticed the outboard bracket was eaten away as well, it looked like white coral. But the zincs we're fine The crazy thing was the owner had just used the boat a week before.
After checking the docks for bad wires and the other boats on the dock we were baffeled.??
When we checked the boat we found a hot wire was connected directly to the bonding system
Turns out the someone in the owners family had replaced the batteries and decided to FIX some wiring problems
The electrolosis was so bad on this boat, mechanics from all over the local area came to take a look at the damage, most of them couldn't believe it. If I can find the pics I'll post them later.

Had a similar one trim tab switch on the dash port side rocker wasn't working, owner bypassed at connected both at transom and left hot wire in bilge.

[jawz12]

There are so many things that cause galvanic corrosion.

Mercruiser discovered a major problem with the older bravo III stern drives back in early 2000 where customers were pulling there boats out and if you touched the skeg it would crumble in your hand.

One of the main causes of that was that with it was dissimilar metals was that they found out when bottom painting bottoms the paint was going all the way up the to the transom assembly there for causing the dissimilar metals between the paint and the drive.

In order to avoid the above problem you need to leave a 1" gap between the bottom paint all the way around the entire outboard bracket or transom assembly.

Another couple things that I have seen happen is electric trim tab cylinders some times fail and explode the case and allows water in there for putting stray current in to the water.

Another problem I have seen is with bilge pumps/float switches sometimes the wire breaks or the connection is actually sitting in the bilge water causing stray current.

Then the ever so common culprit is other boats surrounding you or shore power cords.

The last time I had an issue they almost indicated that if you are an outboard and surrounded by stern drives you are more susceptible to it. Not sure the truth of this but most stern drives here are dukey crusiers.

The document attached is a great tool and put understanding to how it happens

Hope this helps

first...
bravo III drives,the galvanic reaction was caused by the use of a stainless steel prop shaft bearing carrier...ANY and ALL aluminum underwater parts,INCLUDING brackets,need at least a 1" gap between them and any copper based antifouling paint...i see way too many aluminum outboard brackets painted incorrectly...


shore power cords...should not be in the water...keep them outta the water...

wet 12v wiring,this will induce current into the water,it will erode your zincs then attack your underwater gear !!

shore power ground...the shore power ground must NEVER be connected to the ship's dc ground system....

this whole galvanic,stray current electrolysis thing is kinda technical,if you're not sure about it,then i suggest you seek the services of a qualified individual to check it all out for you...