Electrolysis - What comes first?

[KnotConnected]

So, after replacing the lower unit due to corrosion last-minute this spring, I want to make d@mn sure whatever was causing it has been resolved. Before I put her in (1994 Larson Cabrio 280 single 7.4l Merc) I...

1) Stripped the paint around the lower unit about 1" (the bottom paint was all the way to & touching the lower unit)
2) Replaced all anodes (they were pretty worn)
3) Reconnected the grounding wire connecting the port drive trim actuator to the housing (it was disconnected)
4) Verified the mercathode is connected & wired properly.

I'd like to have the water / boat tested for electrolysis, but the meter and electrode are pretty pricey, so I don't want to make the investment unless I still have a problem.

Question being: Will the anodes first and foremost *always* corrode BEFORE the important stuff on the outdrive? If so, I can just constantly check the condition of the anodes, and if they're wasting away too quickly, I'll know I still have a problem.

HOWEVER, if this isn't necessarily always true, and the drive could be corroding *with* the anodes, then I want to pursue a resolution immediately and not wait until the anodes (and lower unit) show signs of corrosion.

 

[Slip Away]

Re: Electrolysis - What comes first?

If you want to be d@mn sure what is causing the problem, test the water it sits in first. In theory, the anodes are "sacrificial" and will go first.
But I have seen the anodes and drive corrode at the same time in some boats.

 

[boatpoker]

Re: Electrolysis - What comes first?

First of all don't take advice from anyone who uses the word "electrolysis" in regards to corrosion on a boat. Electrolysis is a process of chemical change in an electrolyte due to the passage of electrical current through that electrolyte.

What you are talking about is either stray current or galvanic corrosion.

It's not enough to simply install new anodes, you must ensure electrical continuity between the anode and the metal to which its affixed.
Check this with a multi-meter set on ohms and the result should be less than 1ohm. This should help with the galvanic current.

You must also know the right type of anode to use zinc, magnesium or aluminum indium

Stray current may be from your own boat of from a neighbors boat. As soon as you plug in to shore power you are sharing a common ground with your neighbor and you inherit his problems. To avoid this you can install a galvanic isolator for about $100.00.

If you are still not satisfied I'd suggest you hire an ABYC Certified marine electrician to check your boat out. It would take a whole seminar to explain it all here. Or you could even take the ABYC course yourself for a thorough understanding of the issues and solutions.

 

[Slip Away]

Re: Electrolysis - What comes first?

10 to 1 his Larson already has a galvanic isolator installed. Most if not all cruisers do, I know my two boats did.

 

[boatpoker]

Re: Electrolysis - What comes first?

10 to 1 his Larson already has a galvanic isolator installed. Most if not all cruisers do, I know my two boats did.

In the last 2-3 years they have become a little more common as factory installs, before that they are extremely rare.

 

[Ned L]

Re: Electrolysis - What comes first?

You beat me to it Boatpoker. --listen to him as he is correct.
Anodes will protect against galvanic corrosion.
I don't know if anything fully addresses stray current corrosion except for fixing the problem, which can be with your boat, the boat next door, or even the next marina.

 

[KnotConnected]

Re: Electrolysis - What comes first?

Thanks guys! The galvonic isolator is on the list of things to add if not already in. I'll check this weekend, if it was stock, it should be near the ground line close to the shower power inlet, just as an after-market unit would be, correct?

(Side note, thanks for all the help. This boats been one helluva project since I got it, but all the money and headache is *totally* worth it on those days I wake up to a sunset coming up over the islands as I sit on the bow and enjoy the sea breeze)

 

[Thalasso]

Re: Electrolysis - What comes first?

goastnode.

#3 is was one of your problems.If you are serious about checking your protection the silver chloride tester is $100.00. Your drive replacement cost??????.
boatpoker is spot on with the remedy.
you must ensure electrical continuity between the anode and the metal to which its affixed.
Check this with a multi-meter set on ohms and the result should be less than 1ohm. Take the black wire on your DVM and put it on a good ground.(battery) Take the red wire and touch all metal that's to be protected and you will know weather it's grounded properly.

Also if you check with a silver chloride tester when in the water it should read around 900-1100 on the DVM. This tells you how your Mercathode is working. If the reading is to low just add another Mercathode Controller to the existing one. They will be mounted (controller) on top of your engine.Black or blue in color

 

[Thalasso]

Re: Electrolysis - What comes first?

Thanks guys! The galvonic isolator is on the list of things to add if not already in. I'll check this weekend, if it was stock, it should be near the ground line close to the shower power inlet, just as an after-market unit would be, correct?

(Side note, thanks for all the help. This boats been one helluva project since I got it, but all the money and headache is *totally* worth it on those days I wake up to a sunset coming up over the islands as I sit on the bow and enjoy the sea breeze)

It's probably behind the boats electrical panel. All it has connected to it is the green ground wire.Just make sure your shore power is off and disconnected before removing the panel

 

[Thalasso]

Re: Electrolysis - What comes first?

goastnode.

#3 is was one of your problems.If you are serious about checking your protection the silver chloride tester is $100.00. Your drive replacement cost??????.Marine Corrosion Testing - Silver/Silver-Chloride Electrode‎
BoatZincs.com (978-841-9978) – The Online Superstore for Zinc Anodes
for Marine Corrosion Testing‎ $124.00

boatpoker is spot on with the remedy.

you must ensure electrical continuity between the anode and the metal to which its affixed.
Check this with a multi-meter set on ohms and the result should be less than 1ohm. Take the black wire on your DVM and put it on a good ground.(battery) Take the red wire and touch all metal that's to be protected and you will know weather it's grounded properly.