Help! Merc 125 saltwater corrision

[rakidd413]

I have a 125 HP merc saltwater motor, it seems to be getting alot of galvonic corrision, the anodes are in good shape, but the motor is a saltwater version used in fresh water, do I need to put a different type of anodes on it? if not what could be causing the corrosion, I have had the motor since 2002 , and this has never happened before? any help would be greatly appreciated.

Thanks,
Rick

[SabikiRig]

Do you keep the boat in the water with any shore power attached? Or in a marina where there is other boats with Shore Power?

There is obviously some external current from somewhere. Check your electrical system for "leaks".

[SalmonBum]

The reason the anodes are in good shape is because they are Zinc. You need magnesium. The Zinc andoes look good yr after yr, because they are not doing thier Job. Zinc is for Saltwater. An anodes job is to sacrafice themselves instead of the Lower unit. I use Magnesium and notice a HUGH Difference. After a yr, they are half gone.... BUT My lower and beaver Troll have NO Corrosion on them. Cost me $100 a yr to switch over, but well worth it. Wouldn't keep my boat in a slip without it

[SabikiRig]

The reason the anodes are in good shape is because they are Zinc. You need magnesium. The Zinc andoes look good yr after yr, because they are not doing thier Job. Zinc is for Saltwater. An anodes job is to sacrafice themselves instead of the Lower unit. I use Magnesium and notice a HUGH Difference. After a yr, they are half gone.... BUT My lower and beaver Troll have NO Corrosion on them. Cost me $100 a yr to switch over, but well worth it. Wouldn't keep my boat in a slip without it

Salmonbum,

You pretty much covered where I was going next.

He would probably not notice any corrision with Zinc if he trailered the boat.

[SalmonBum]

Yep. If the boats not slipped and is just trailered, no biggie. Most of the corrosion comes from stray current at the docks. You can do everything you can to your boat to stop YOUR boat from causing it, but if the docks power and the other boats arround you don't do the same, your still gonna get corrosion. The way to help battle that is with the proper anodes, magnesium for freshwater

[salmonslammer]

Hmmm...Never knew that.

Is the corrosion a result of electrical current or just sitting in the water?


We'll have to go do some fishing when your brother gets back from wandering around South America...

[SabikiRig]

Hmmm...Never knew that.

Is the corrosion a result of electrical current or just sitting in the water?


We'll have to go do some fishing when your brother gets back from wandering around South America...

Stray Current from Shore Power and/or boats that are poorly or incorrectly grounded.

Speaking of anodes, I may have to replace the ones on my Alpha1 this season. They are not looking too good.

[Jason Adam]

Is the corrosion a result of electrical current or just sitting in the water?


Both. It can be caused from stray current in a marina, or it can be caused by any two dissimilar metals in water containing any alkaline(most water with any salt or metals), effectivily making a battery, hence, stray current.

[FIJI]

thats the exact same OB thats on my boat. But mine is trailered.

[rakidd413]

pulled the boat out of the water and found a broken ground strap located under the little plastic cove on the port side of the engine shaft, put on a new one and no more problems.......Thanks

Rick

[KI Jim]

I too have the exact same engine (but I trailer mine)-good to know!

Jim

[FREEPOP]

Here is a table of common materials in order:

http://en.wikipedia.org/wiki/Galvanic_series

Lots of info there to be found too.

Sea water conducts electricty much better than fresh. Zinc and magnesium are sacrificial anodes, meaning that they will corrode, disipate and have to be replaced. Any two dissimilar metals in water will have galvanic corrosion, because one will be more noble than the other.