electrolysis on bracket

[panga]

I have been noticing some pitting on my bracket. Boat is a 2520 with twin 150s, 1992 model. I am assuming this is from electrolysis. The pitting is in a line about midway across the top surface of the bracket, looks like small pitted holes and peeling paint. I recently had the bottom done on the boat and the previous owner had painted the bracket, so the guy went over it this time again and replaced the zincs. I am assuming this new copper paint could be causing my issues, it seems to be much worse since the repaint.

What can be done, do I need to strip all paint and resurface the bracket with something? If the bracket is stripped does it need to be re etched? What kind of paint and primer?

Thanks

 

[miky2884]

If he painted the bracket with a bottom paint containing Copper, you got a problem on your hands, it will need to be striped and redone. You need to use Trilux 33

 

[DaleH]

That pitting is caused by Galvanic Corrosion, caused by dissimimilar metals in contact with each other and only exacerbated by electrolysis, which is an electrical reaction (ion exchance) with saltwater as the electrolyte.

Aluminum brackets should never be painted with a copper-based anti-fouling paint. Not sure if the original owner did and the one who repainted it repeated that error, but regardless - you now have a mess on your hand.

After you strip it, mechanically, chemically, or by soda blasting, you'll need to etch it with a zinc chromate or strontium chromate paint, of which Aluma Protect by Pettit (epoxy-based, so it's durable) is what I have used on many aluminum boats. Once stripped, solvent wash it well with acetone and plenty of clean rags, working in one direction only, immediately before painting the etching primer on it.

Then you can apply Trilux 33. I wouldn't apply Tlux-33 without the eching base coat. Spec sheet on AP attached.

Aluma Protect is an epoxy primer specifically formulated for use on sand-blasted aluminum where maximum corrosion resistance to fresh and salt water is required. Coating is resistant to water, as well as, many chemical fumes and very humid environments. Pettit Protect High Build Epoxy 4700/4701 is usually used over the Aluma Protect for bare aluminum, pontoon hulls, and outdrives.

 

[Bryan 2530]

Yep, you need to remove all that copper paint.

Is the pitting underwater or above the water?? Sounds like the bracket deck from your description.

FWIW, I touch up any corrosion on my bracket every year. It keeps the bracket looking better longer.

Any small chip or bit of corrosion is sanded and painted over.

 

[panga]

Yeah figured Id have to strip the paint, The pitting is in two horizontal rows going the direction of the transom or beam, about a foot apart and about a foot in from the front and rear edge of the bracket. Im assuming this is where horizontal ribs are running and the welding made the metal more susceptible to the pitting.

How imperative is it to remove every spec of the copper based paint? Im hoping to not have to pull the motors and bracket from the transom.

Also how fast does this act? I have some free time between jobs in late january, and would like to tackle it then if time is not super important.

Also is this only occurring when the boat is in the water or will it happen the trailer.

Thanks

 

[gw204]

Pulling the motors isn't hard and you don't have to remove the bracket from the boat (unless the transom to bracket seal is leaking).

I went though a similar thing with my old 25' Grady. While the bracket didn't have any galvanic corrosion, the Gil-coat had separated from the aluminum (but not chipped off) and there was some corrosion from saltwater.

I ground off all the separated spots as well as everything above the waterline to a point about 3" below the bottom paint line and filled in some low spots with the version of Marine Tex suitable for use on metal.

\

I then had the portion of the bracket above the bottom paint line shot w/ Awlgrip.

Next I taped off the Awlgrip and existing bottom paint. The tape at the top was actually about 1/4" up the Awlgrip and that area was lightly sanded with 80 grit. Next was to etch the bare aluminum with the West System aluminum etching kit. It the the product number is 860 or something like that. I followed the instructions exactly. I didn't take pics of that because there wasn't really anythign to see. One of treatments was clean, the other a very light yellow.

As soon as it was dry, I applied several coats of Interprotect 2000E and peeled the tape.

New-to-me motors went on and were re-rigged.

Ran a fresh bead of caulk around the top and slightly down the sides of the bracket (for cosmetic purposes...I had done the rest of the sides and bottom a few years prior). Taped off the paint line and reapplied the bottom paint. No paint on the engine mounts. I just dabbed it on with a 3" chip brush to more closely match the existing paint text left by the roller.

FYI...the paint I used was standard copper-based paint. That's what the PO used for the 13 or so years he owned the boat and there was zero galvanic corrosion. The key is to keep it off of bare aluminum.

I sold the boat a few weeks later so while I can't tell you how it's holding up, but I would be very surprised if there are any issues with it.

 

[panga]

the paint I had applied was put on over old bottom paint, not sure if it was copper based or not previously, the new stuff definitely was. So... the new stuff isnt touching any bare aluminum. It just seems odd, that I noticed this after re doin the bottom. We replaced the zincs on the bracket, the old ones were painted over and not doing much good.

The boat has been spending more time in the slip.

 

[DaleH]

The boat has been spending more time in the slip.

Well that clearly could be a contributing factor ... as any stray current in the water is going to make a super conductive environment that will greatly exacerbate any effects from galvanic corrosion or electrolysis, which has a symbiotic relationship.

 

[panga]

After some further investigation, I figured out that the bracket is stainless steel, made by stainless marine, does this change anything ?

 

[Bryan 2530]

Not really.

 

[Megabyte]

Stainless Marine is the company name, but the bracket is not made of stainless steel.

http://www.stainlessmarine.com/index.ph ... t&Itemid=1

 

[miky2884]

Kevin is correct I have the same bracket and its aluminum, they used these on the older Parkers before they went to Armstrong

 

[Bryan 2530]

Being a 92 though, it may be stainless.

That is where the name came from, I assume it has no swim platform??

 

[miky2884]

good point, forgot it was a 92 hull

 

[Megabyte]

Mine is a 96, no swim platform, aluminum.
A bracket made in stainless would be very, very heavy.

 

[Bryan 2530]

They are, a friend of mine put a Stainlees Marine bracket he bought off craigslist on a 1988 Soportcraft he had and it was actually stainless steel.

I don't know what Parker used for this vintage.

 

[miky2884]

Bryan Irish Mikes bracket is stainless ? I did not know that, his boat does sit low in the back

 

[Bryan 2530]

Not Mikes', Jeff's boat "Finito".

 

[panga]

Yeah Im not sure if it is stainless or aluminum, but def made by stainless marine. The issue did not come up until the redone bottom, so Im gonna strip and repaint it.

 

[Bryan 2530]

Good choice.