electrolytic pitting

[belercous]

My boat maybe about dead. I pulled it out of the water yesterday for the first time in 2 years, & today power washed the algae off the logs. They have hundreds of small spots of electrolytic corrosion. Scraping the bumps away reveals salt powder & pits, some fairly deep. 2 years ago (when I was at a different marina) these spots were not there. I was told that there was current in the water at the slip which caused this.

Ironically, while my buddy wash washing the pontoons I was replacing the sacrificial anode which was overdue to be changed.

Is there a way to fix this problem? Could I paint the logs to prevent further degradation? I don't know what to do, but if I were to put the boat back in the water without fixing it it'll be less than a year before the boat will sink. I am beside myself.

[belercous]

I just read where zinc anodes should be replaced yearly. The anode had not been replaced for over 10 years, if ever, & sorely needed it. I only have one & it's on the trim bracket. Should I mount another one on the 3rd (actually 1/3 of a 3rd) log as well so as to better protect the logs? The boat lives in the water is only taken out for a few days a year.

I'm going to try to find an electrician who can check my slip for stray voltage before I put it back in the water. I'm also going to contact a couple places which paint aluminum hulls to see if that'd be the way to go, but I don't want to have to repaint the things every year or two cuz that would get expensive.

I've got an aluminum welder who can apply welds in the deep pits, but there are a bunch of them & I also want to see what's on the logs where they sit on the trailer. I'm not sure how to go about lifting the boat up (I'll prolly have to do it in spots as the boat is fairly heavy).

I'm going back Thurs to wire wheel off the corrosion spots to judge the full extent of the problem. The welder said to use a SS wheel rather than brass. I'll be gentle on it. I am still in a panic. I don't want to lose my boat because it can't be replaced. (The newer Party Cruisers are not near as well laid out as the old ones. Driving from inside the cabin is screwed & it reduces the room in the cabin as well.)

[FogHorn]

STOP! Do NOT use a SS wheel on your aluminum tubes! That is a rule taught to all aircraft mechanics because the stainless wheel will leave minute particles embedded in the aluminum and will contribute even MORE to corrosion. Stainless and aluminum are contradictory to each other for electrolysis.

Use aluminum-wool or 3-M pads or wheels which are synthetic.

Another thing about “zincs”. Zinc is wonderful for salt-water...not so much for fresh water....and may partially be contributing to lack of protection for your aluminum tubes.
Aluminum anodes are used for salt AND/OR fresh water. And Magnesium is best for Fresh water only.

[belercous]

I was also taught in A&P school not to use SS on AL. The welder who's going to install my drain plugs told me to to do that & I questioned him about it. He said he's been welding AL for decades & it's never caused a problem. I tried using Scotch-Brite pads, but that didn't go very fast. Even with the SS wire wheels I figure I'll have a good 20 hours in prepping the pits. While the SS wheels will transfer some metal, it will be microscopic amounts which shouldn't cause much of a problem with galvanic action. Surface corrosion is nothing compared to the electrolytic pitting I've got going on.

After I researched it I found that zinc is only for salt water. I replaced my anode with a new Mercury part which says it's an AL alloy. It needed replacing, prolly a couple years ago.

For the pitting I've found an AL brazing material which requires the AL to be heated to 735 degrees & then rub the rod onto it. I'll go back once it cools & contour it to shape. The brazing material contains Zinc, but since Zinc doesn't work good as an anode in freshwater it should be alright. Check: https://www.youtube.com/watch?v=LB8qw-u9XVI&t=113s

To get under the logs where they sit on the bunks I'm going to use the piering jacks (or whatever they're called) found in basements to support & level floor joists in houses, doing one side at a time.

I'm thinking about removing the batteries once I get it back in the water for the winter rather than keeping power on the boat to keep them charged.

[FogHorn]

Belercous, those so-called aluminum brazing rods are junk, and I don’t think you’re going to be able to heat the tubes up that hot without introducing serious buckling and warping. I’d suggest you polish the corrosion and don’t try such repair schemes. Certainly don’t do it until you’ve experimented with some scrap first.

It sounds as if your moored boat is suffering from stray electrical currents, possibly from other boats in the marina if not from your own while it’s hooked up to shore power.

There are cathodic devices for boats that are moored and suffer electrolysis you might look into if this is that serious. Google “Marine cathodic protection systems”

Here’s a quick read on the subject: http://www.galvatest.com/WP_Cathodic_Protection.pdf

[belercous]

Thanks for the link Foghorn, I'm gonna read that soon. It seems to be right on point & better info than I've found. I'd rather my boat be a cathode than an anode. I don't know if this was caused by not changing my anode in time (I believe it was original to the boat), but it was overdue.

Some of those pits are too deep to polish out, looking like 2/3 of the depth of the metal. It'll require MAPP gas to get the metal up to temp (735 F) which is about 500 degrees below the melting point of AL. My buddy has one of those devices which one just points at something & it tells the temp so that may speed things up, marginally.

It looked pretty easy in the video & I'll trust brazing more than epoxy. Another video shows a prop blade having a missing chunk being repaired (I'd have that done professionally) & the guy beats it with a hammer. I can't let a lot of these pits go unrepaired. This is gonna be a very time consuming job, but I believe it'll do the job. https://www.youtube.com/watch?v=-yr2XjmLEoY

[Moser]

I watched the demo. he's a bit of a snake oil salesman, he beat the prop pretty hard, but at or below the repair line. If you can get the rod to flow like it does on the prop suface for him, it should fill your pits.

[belercous]

I went to the boat today & tried the AL brazing with moderate success. It's gonna take me a bit more to get the hang of it, but I believe it'll work. The job is gonna take many hours though. First I went over the pits with a wire wheel. But I need to clean to bare metal the all salts left in the bottom of the pits. A sharp pick & a pocket knife blade is not very fast so I'm gonna take my Dremel with tiny carbide grinding burrs & see if that's any faster (it certainly can't be any slower). Then, once I've filled the pits in I'll need to grind down the excess to contour. 120 grit sandpaper is way too slow so I'll be experimenting with other methods.

I've got a guy who'll test my slip for stray current once I get my boat back in the water so I'll know if it was the marina's fault or mine. I'm also going to install another anode on the left pontoon on the transducer mounting bracket.

I figured that it'd cost me a fortune buying small containers of MAPP gas @ $12/bottle so I stopped at a welding supply shop & priced a small tank of MAPP gas. They lease them for 5 years w/1 fill will set me back $150, but should be enough to complete the job. I have a friend who'll loan me a regulator/nozzle set-up & hopefully it has a bigger flame so I can heat a larger area faster than the small unit I have (which takes a bit longer than the guy in the video, which somehow doesn't surprise me).

They also had the same type of brazing rods for a reasonable price so I picked up what I hope is more than enough to do the job.

[Captain Tony]

Hey Belercous:

Wow what an undertaking. Here's hoping the end result is what you want it to be.

You realize of course that we will need pictures posted at many times during the process just to be sure your armchair superintendents approve of your skills, lol,
but seriously bless you for taking on the labor and saving that beautiful ship.

Stay Healthy

[Moser]

Be careful with that carbide burr, they eat material. You can poke a hole in a tube in the blink of an eye. Try a small area with some plumbers flux brushed on thin, it may encourage the molten material to flow.