Outdrive corrosion out of control

[Pachanga Boy]

okay, so I've finally gotten to see my boat since it's been pulled out of the water (sad I know) and crawled behind the boat to see that it looks as though the outdrives have been swimming in acid all summer.
when I bought the boat they were in rotten shape, I scraped them down, cleaned them up, primed and painted them and installed new anodes in the trim plates....from the looks of it you'd never know I did a thing last spring. I'm figuring I need to start by checking my mercathode system both the anode under the drive and the wiring, is there anything else I should check. also is there an easier way to clean these things up, I'm almost thinking I should pull them and have them media blasted.

just to give you an idea of how much corrision we're talking here.
spring before all the time and effort

after all my time and effort

last week:smt009
porous anode

 

[Ididntdoit]

#1 - where are your trim cylinder anodes - I dont even see bolts?
#2 - you need a 1" unpainted ring around the outdrives - bottom paint should not touch the outdrives - it causes a disimilar metals issue
#3 does the boat have a galvonic insulator installed, is the bonding system in good shape?
#4 any electrical problems on your boat
#5 any electrical problems on neighbors boat? are you in a known "hot" marina

judgeing from the first set of photos the problem is with your boat - you cleaned up the drives but did not fix the cause...

 

[psubill78]

I'd definitely get a corrosion reference electrode and check out - somethings not right?

When you finished your drives, what did you use to sand them down? Possible that you left shavings in under the paint?

 

[JV II]

#1 - where are your trim cylinder anodes - I dont even see bolts?
#2 - you need a 1" unpainted ring around the outdrives - bottom paint should not touch the outdrives - it causes a disimilar metals issue

This

 

[Pachanga Boy]

well, I never see any boats on Erie that have a 1" ring around the outdrives on their bottom paint, so I don't think that's really the issue. what is a "galvonic insulator", and how do I check the "bonding system" is that the mercathode system?

 

[dicor]

I'd sand them down do not use a metal brush. Then put on 3 coats of Interlux Primco then 3 coats of Interlux Pacifica Plus. Talk to the support folks at Interlux they will guide you through the steps. FYI putting the first coat of Primco on before the corrosion begins is important. Make sure you are using the correct anodes for the water your slipped at. Ditch the present (blue or black) Mercathodes and replace them on both units with the new High Output Red Mercathodes.
Buy a Mercathode test probe and test it twice a month, it attaches to a multimeter. It's not cheap around $125 but a lot cheaper than replacing both drives.
You'll see that kind of corrosion with stray electric at the dock. A dead battery, loose/missing ground a neighbors boat with electrical issues. I would also talk to other folks that slip there. Walk around the yard now while the boats are on blocks and look at their out-drives, if they look like yours do I'd start hunting for a new Marina.

 

[Jetmart]

I'd sand them down do not use a metal brush. Then put on 3 coats of Interlux Primco then 3 coats of Interlux Pacifica Plus. Talk to the support folks at Interlux they will guide you through the steps. FYI putting the first coat of Primco on before the corrosion begins is important. Make sure you are using the correct anodes for the water your slipped at. Ditch the present (blue or black) Mercathodes and replace them on both units with the new High Output Red Mercathodes.
Buy a Mercathode test probe and test it twice a month, it attaches to a multimeter. It's not cheap around $125 but a lot cheaper than replacing both drives.
You'll see that kind of corrosion with stray electric at the dock. A dead battery, loose/missing ground a neighbors boat with electrical issues. I would also talk to other folks that slip there. Walk around the yard now while the boats are on blocks and look at their out-drives, if they look like yours do I'd start hunting for a new Marina.

The 4 boats that I have owned on the Great Lakes all had the 1" space around the drives. I believe most boat manuals instruct you to this as well as the directions for applying bottom paint. Don't underestimate this detail.

 

[dicor]

The 4 boats that I have owned on the Great Lakes all had the 1" space around the drives. I believe most boat manuals instruct you to this as well as the directions for applying bottom paint. Don't underestimate this detail.

Jetmart is absolutely correct most all bottom paints have a high copper content (marine growth does not like copper) with the copper paint right up against your aluminum out-drive you'll in essence create a battery.

 

[GrandMaster]

Its definately supposed to have a gap between the drive and bottom paint.

 

[psubill78]

well, I never see any boats on Erie that have a 1" ring around the outdrives on their bottom paint, so I don't think that's really the issue.

I see lots of large women who like to wear tiny spandex at Walmart also - it doesn't make it right.

The 1-2" is imporant. Check your stern drive user manuals.

 

[kaz911]

I see lots of large women who like to wear tiny spandex at Walmart also - it doesn't make it right.

The 1-2" is imporant. Check your stern drive user manuals.

The 1-2" is ONLY important if the bottom paint contains copper. You can safely use water based copper free paint on that inch without any issues. My boat has CopperCoat - with 1 1/2 " space - and then water based anti fouling paint on the rest.

But I would say - apart from Anodes missing - check that you have ALL the continuity wires connected and they are operational! They help ground the drives and without them you are inviting to a corrosion party. Also check the ones on the engine to the transom plate.

And before you upgrade Mercatode to RED - check the ones you have work with the silver coil from Mercruiser. The RED ones uses twice the power and might not be needed. But everything else first!

And you have a lot of "loosish" wiring on the back. Check them as well - if one is broken it can create a circuit.

From the pictures it looks like the starboard drive has taken a harder beating than the port. So start there and compare if there are any wiring differences.

 

[Lazy Daze]

All of the above recommendations are correct and should be addressed.

But... I'm looking at the pictures and I don't really see any "corrosion". It looks like some sort of calcification or something from the water. Look at the first and second picture - you can see the same white crap on the drive and both the swim platform support and trim tab ram. In looking at all the pictures, I'm hard pressed to find any spots where the drive looks deteriorated (corrosion). It appears the paint has worn off (third picture), but that could be due to an inferior paint (prep) job.

Do you only have a cavitation plate anode?

I would also encourage you (as mentioned above) to double check ALL of your grounding/bonding points/electrical connections in the boat. ALL of them. Are the drive's bonding wires present (both outside and inside the boat)?

 

[psubill78]

Is there a way to test grounding outside of the water. A guy from boatzincs.com told me to use a meter on the anodes and drive parts to test to make sure there's continuity.

If someone had that process documented - that would be a big help I'd suspect.

 

[KC_Sundancer]

With fresh water you may also want to be using Magnesium Anodes. Salt water is more conductive than fresh. In fresh water, the more noble zinc or aluminum anodes do not break down as easily which allows for more corrosive action on the aluminum of your outdrives.:huh:

 

[Lazy Daze]

With fresh water you may also want to be using Magnesium Anodes. Salt water is more conductive than fresh. In fresh water, the more noble zinc or aluminum anodes do not break down as easily which allows for more corrosive action on the aluminum of your outdrives.:huh:

BUT, be careful. Sometimes Mg can overprotect and cause corrosion... which usually starts as "paint lifting/peeling". Aluminum is usually the safest choice if not sure about the condition of the water. But the best way is to ask EXPERIENCED locals what they use.

 

[KC_Sundancer]

BUT, be careful. Sometimes Mg can overprotect and cause corrosion... which usually starts as "paint lifting/peeling". Aluminum is usually the safest choice if not sure about the condition of the water. But the best way is to ask EXPERIENCED locals what they use.

Here is a good link to a web page that describes in detail how they work and the "over-protection" Lazy Daze noted: http://www.performancemetals.com/anodes/AnodeFAQs.shtml

 

[JV II]

well, I never see any boats on Erie that have a 1" ring around the outdrives on their bottom paint, so I don't think that's really the issue. what is a "galvonic insulator", and how do I check the "bonding system" is that the mercathode system?

No corrosion, just pesky barnacles.