Question(s) on Hull Corrosion

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minuteman62-64

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I have an '82 Bayrunner, by Westcoaster. Pretty sure the hull is 5200 series aluminum. Got some corrosion under the bunks (see attachment). The boat sat for about 20 years on old degraded carpet and moldy bunks. I'm pretty sure the corrosion was already there when I replaced the bunks and put on new, quick dry, West Marine carpet. Just to make sure, I'm thinking of adding some of those "Glide Sticks" (from West) this winter.

Anyways, no sign of pin-holes/leaks from this corrosion. So, my question: should I leave this alone or is there some sort of treatment that will "stabilize" it?

Am I correct in assuming that the corrosion is somehow related to the bunks? Adding Glide Sticks a good idea?

Hull Corosion.jpg
 
That's poultice corrosion, from being in contact with a wet surface, such as carpet or wood.
Use a stainless wire brush to remove the excess, then treat with ospho (phosphoric acid) Then use self-etching primer, or zinc chromate primer, followed up with paint....or preferably, good bottom paint like Trilux 33.
 
****, I was hoping the answer would be more like ".... spray some WD-40 on it and go boating" :)
 
Hadn't heard the term "poultice corrosion" before. Lots of on-line info on what causes it and how to prevent it, not much on what to do if you have it.

Raised boat off bunks. Only area that seems impacted is just at the front end of each bunk, as shown in previous photo. Attached is shot of the starboard corroded area after scrubbing/wire brushing/sanding off the loose stuff down to bare aluminum. Some deep pitting, but nothing going all the way through.

Appreciate the suggestion on painting, but thought I'd try Marine Tex. I've used the grey on pin holes on my transom and it's holding strong for 4 years now. Talked to the tech support folks at Marine Tex and they said the white actually has better adhesion than the grey. So, that's where I'm going for now (subject to regular monitoring to see how it holds up).

Process will be to remove corrosion down to bare, roughed up, aluminum, clean with acetone and apply Marine Tex. The Marine Tex folks don't recommend any chemical prep, as they do for Gluvit.

I'll post results.
 

Attachments

  • Polutice Corrosion.JPG
    Polutice Corrosion.JPG
    53.6 KB · Views: 647
OK, repairs completed. Here's starboard side, white Marine Tex applied and sanded to a feather edge. Same on port side. This will be a good test of the Marine Tex since it will be subject to moving salt water plus sliding on and off bunks.

Checked along the remaining areas that overlie the bunks while the boat was raised. Only a couple of small spots, nowhere near as severe as the ones I fixed. During the Winter lay-over (January 15-31 here :) ) I may pull the bunks for access and give those remaining spots a similar treatment (assuming the current repairs hold up).

Interesting how the worst areas were just overlying the fronts of the bunks - based on my reading, must have been ideal chemical/physical conditions in those areas.
 

Attachments

  • Hull Corrosion Repair Sep14.JPG
    Hull Corrosion Repair Sep14.JPG
    21.2 KB · Views: 613

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