Klamath 19 Corrosion

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Joined: Sat Nov 12, 2022 9:06 am

Klamath 19 Corrosion


Post by ModG »

Hello to all.  First, let me contribute a profound thanks  to those who have offered their time, ideas and experience on this site.  I’ve been reading last few weeks since I’ve purchased my first alum boat.  Previously I owner ad 24’ glass boat and after selling always wanted an aluminum.

So, the “new” boat.  It’s a 2004 Klamath.  Purchased and didn’t know much about alum corrosion beforehand.  Used primarily in salt.  Original owner was neighbor of family member and I heard he took good care of the boat through the years, and that it sat (mostly) covered last 8-10 years.

Found no obvious holes in bottom, did a couple test rides with no obvious water intrusion after pulling plug, hull looked pretty darn sound…then I took off the deck a week after.  Discovered decent amount of organic material, somewhat dirty styrofoam, and some corrosion.  Worst if the corrosion is in the bilge, within a few feet of the drain plug.  Poultice corrosion it would seem.

I’ve since removed all foam, washed clean and rinsed heavily, Green 3M, then sanding with 120 and 400.  I can’t find any holes, but there do seem to be a few tiny corrosion pits, like around 1/16th -1/8th diameter and same depth perhaps, that are in some flowering spots before I removed the flowering.

So no obvious holes, but some localized very small Swiss cheese near drain plug on bottom.  Here and there on rest of the bilge has a few spots of flowering that seem to have some less obvious pits.

My current fix is to continue with etching with either alumibrite or shark hide, then boshield the complete bilge, then pray.

My buddy does own a welding shop and I will have him fix a few deck braces that have small cracks where center console attached.  From what I have read in this forum, welding may not be needed.  But if it is, I’d have to drill out all pits, and make sure my welder had experience with the thin material.  Then pray.  Or, perhaps a patch, which seems difficult considering the bends in the hull from the bottom chines.

AAaaaamd now my question please:  Should I just boeshield after etching, and monitor?  Or should I try other material filler first from the top/inside of bilge to fill the pits, then paint?  Or fill with 5200 and paint?  Or just paint? What about braising with flux and “pooling” over the areas?  

I keep going back and forth on what my situation might call for, it doesn’t look like it’s comprised the hull too much yet, doesn’t leak from what I can tell, but I’d like to take some action.

Any thoughts or guidance appreciated!



Posts: 2
Joined: Sat Nov 12, 2022 9:06 am

Re: Klamath 19 Corrosion


Post by ModG »

Couple photos…note that I have not washed out there pits/corrosion spots just vacumed…some debris in there still from sanding etc
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Donator 08, 09, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24
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Your location: Kenai, AK
Location: Kenai, Alaska

Re: Klamath 19 Corrosion


Post by kmorin »

ModG, welcome to the ABB.com Forum and the discussion of aluminum boats. 

Manufactured boats are very often not made of the (main welding) ‘marine alloys’ that is; 5000 series sheet/plates and 6000 series extrusions. The forming process of rolling ridges into sheets or pressing or stretch-forming isn’t done very often with the 5052, 5083 and 5086 primary alloys used in plate welded boats.  As a result corrosion resistance or existence between the formed-shape boats and the ‘five panel’ welded boats isn’t identical- similar, yes- but not identical. 

My remarks will be based on my experience with the formed panel and welded seam boats like your post shows. I don’t know the alloy of these boats but we can see what’s happened in your pictures. 

No aluminum boat should have a composted organic saturation of the bilge water- the longer it’s left the worse it gets in terms of creating crevice/poultice corrosion cells that can actually puncture the hull; especially in the bilge where the water was allowed to stand. 

IMO using solder like products or flame/torch heating to flood any molten metal onto the sheet areas- isn't very successful. The reason is distortion and lack of exact control of the heat- which is mostly judged by the puddle fluidity. That means when the sheet cools there will likely be huge differences in thickness which will make for areas that are more rigid that others’ immediately adjacent and actual cracking usually follows. 

The same is true, to some degree, with TIG welding. However, if you take out an area of a palm of hand or greater then you’d be more able to control the welding patch. Filling pin holes in super thin sheet is possible but the welder needs to have lots of experience with this type of repair to avoid putting big (quarter sized) thick patches which will then crack out. 

IF you can sand or soda blast then adding an epoxy of some kind may work? However, the odds of the catalyzed resin adhering to the metal is low if you are unable to get some anchor pattern - which you’d expect from blasting. If you blast then softer materials are needed as the medium- NOT what you’d use for steel! 

If you are able to wash/etch the entire area w acid (Zep-a-Lume works well) and clean out the bottom of the pits, then get a very thorough rinse of the entire area - then follow with some Allodyne (Chromic acid to form a chrome oxide layer adhering to the parent metal) then coating with a ‘flexible’ epoxy paint (not a casting or rigid cured product) you’d probably have the best cure for what you’ve shown. 

Both blasting and acid washing will clean out the pits much better than simply using a wire brush or sanding disc. So both of them are farther along in curing the pits by cleaning them out compared to mechanical tools. 

Oils like BoeShield are not a ‘cure’ for thin spots but they will stop the corrosion cells from advancing if the oil is able to get to all the sites. As open as your bilge seems in the photos, you should be able to get it sprayed into the effected areas to stop further corrosion. 

Green labeled soap/cleansing products often have copper solutions in them. For example ‘Simple Green’ (tm) states in the MSDS; “ not for use on aluminum “ as the copper in solution will adhere to and form a galvanic cell which will really give your boat some problems. I suggest you make sure to read the cleaners’ MSDS sheets for content and avoid any that have copper in solution. 

As to pitting being closer to the drain fitting? Was the drain plug the common BRASS cam-over rubber expanding plug? That brass would have left lots of copper ions in the bilge water which we’d expect to pit the area of any exposed bilge water to the hull. SS bilge plugs are much less corrosive to the bilge. I suggest removing the bilge plug completely from the drain and the not leaving it lay in the bottom while the boat is stored/beached. 

Good luck, hope something in all that above was worth your time to read?

Kevin Morin
Kenai, AK   
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