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Thread: electrolytic pitting

  1. #1
    Join Date
    May 2013
    Location
    Edwardsville, IL
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    296

    Default electrolytic pitting

    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.
    1994 Tracker Party Cruiser
    115 hp Merc, 2 stroke

  2. #2
    Join Date
    May 2013
    Location
    Edwardsville, IL
    Posts
    296

    Default

    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.)
    1994 Tracker Party Cruiser
    115 hp Merc, 2 stroke

  3. #3
    Join Date
    Aug 2019
    Location
    Central Texas
    Posts
    84

    Default

    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.
    2015 SouthBay 522FCR w/150 Yamaha

  4. #4
    Join Date
    May 2013
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    Edwardsville, IL
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    Default

    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.
    1994 Tracker Party Cruiser
    115 hp Merc, 2 stroke

  5. #5
    Join Date
    Aug 2019
    Location
    Central Texas
    Posts
    84

    Default

    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
    2015 SouthBay 522FCR w/150 Yamaha

  6. #6
    Join Date
    May 2013
    Location
    Edwardsville, IL
    Posts
    296

    Default

    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
    1994 Tracker Party Cruiser
    115 hp Merc, 2 stroke

  7. #7
    Join Date
    Jul 2006
    Location
    Raystown Country, PA
    Posts
    2,223

    Default

    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.
    Last edited by Moser; Today at 12:56 AM.
    2006 Forester 19 Fish (new deck and carpet, Pontoonstuff interior, 2019)
    1996 Mercury 50 ELPT4S
    1983 Sea Nymph FM171 Striper (complete rebuild from hull up, 2014)
    1985 Johnson 70 J70ELCO

    Raystown Country, PA

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