Pitting in Aluminum Water Tank - Major or Minor Concern ?

[sdowney717]

I know, it might not be a food safe coating, just appears to be, I never noticed it degrade except when exposed to UV sun. And the company has no point to testing for that as that use is outside what designed for.

Over the last 10 years, I must have used a few hundred 30 oz tubes. Ground it, sanded it, breathed a lot of PL dust, got it all over my skin and never felt a thing.

You can mix PL with sawdust or anything dust like really and it will cure full thickness to a nice sandable (with coarse) filler material. Good for plugging holes and rebuilding repairing wood. I also rebuilt rocker panels on a Ford with aluminum sheet, rivits and PL mixed with sawdust to recontour the shape. It is a great seam sealer expanding adhesive to glue and gap seal between metal sheets.

I have even repaired cracked plastic radiator end covers with PL and sawdust and it holds up, for that needs around 1/4 inch thick layer.

It bubbles and swells when exposed to moisture during the cure phase.
You can use a plastic cereal bag to press down the bubbles during the cure as it wont stick to PE plastics.

So far going on 6 months and no leaks.
This is why I KNOW it holds up to heat.

[sdowney717]

just another FYI, if you use PL to repair plastic radiator, take a weller soldering gun and slightly dimple, crater and, carbonize the surface as an aide to the adhesion. I have read before that by carbonizing surface layer of plastic impossible glue jobs can be made to work.

One advantage also of PL is it is flexible and slightly stretchy, so it can give or yield a little where as an epoxy might crack.

Look up Dragon Shield polyurea coating on youtube for some fun.

[GordMay]

Originally Posted by Billy Higgins

sdowney - A lot of that fear of aluminum cooking pots came from popularized medical research in the 80s that noted that some of the compounds in the dentrites in the brains of Alztheimers corpses contained aluminum salts. However, the connection of aluminum cookware to Altzheimers has since been disproved.

Also, I would really think twice about using polyurethane construction adhesive for a potable water tank coating. It's the "construction adhesive" part that alarms me. Polyurethane is not bad per se, but make sure what you are using is ANSI NSF Standard 61 compliant. That is the ANSI potable water standard, and if the label does not state it, I would certainly not use that coating.

INDEED!

[estarzinger]

Originally Posted by Cheechako

2mm is .080 inches. That would be a concern to me, unless those are real thick tanks. They could be .125 thick... which only leaves about .04" left. I guess it comes down to how hard is it to replace the tanks ... just in case. Is it only on the bottom plate? I have heard of just welding a new bottom plate on tanks that are otherwise good. If the tanks are as thick as that baffle I see, I wouldnt worry I guess.

The bottom plating on the 395 is 8mm thick 5083 H111. So, if the pits are 2mm deep there is 6mm left, which is probably plenty.

Originally Posted by Billy Higgins

Evans - Are your water tanks aluminum and integral to the hull on the Hawk?

Yes, integral fuel and water tanks. Water tanks are painted inside.

And what are your opinions on integral sea-water ballast tanks for performance-oriented cruising with a metal hull? Is the trade-off of complexity and loss of storage space worth gaining some stability for performance and comfort, plus having the "double bottom" benefit?

Water ballast tanks need to be right outboard as far as possible, typically right under the deck edge, so they don't really provide much "double bottom" benefit.

I think most cruisers would be better off using the space for stowage or 'real' tankage (eg fuel or fresh water). I have seen a couple boats with fuel tanks (or fresh water tanks) in these outboard locations, with the capability to pump/tack the fuel from one side to the other. That seems like a more practical cruising approach but it still adds complexity, and probably adds some extra small amount of drama to accidental gybes and such.

I don't think I would do it, but would have to see an analysis of how much sailing benefit it would provide. My guess (based on carbon vs aluminum mast analysis I have seen) in cruising terms is not so much.