Corrosion in water tanks on a GB42C

[Bongi]

Folks, this video by John over at Oxford Yacht Agency scares me a little as l consider how we can treat our water tanks to keep the water potable.

To be fair… I think our 1986 GB42C has steel water tanks and John was showing an aluminum tank from a more recent model GB36.

What should I be concerned about when adding a water sanitizing chemical, like a little bleach for example, to prevent contamination of our tank water?

I know the mild steel tanks should also be well cared for…lest they start corroding from the inside.

 

[Each finger a marlinspike]

For the very reasons he mentions aluminum is a bad material for water tanks, although lots of boats have them. This is from the ABYC standards for water tanks and water systems:

23.6.3.2 Materials in contact with potable water shall be nontoxic and comply with the EPA Reduction of Lead in Drinking Water Act amendment to the Safe Drinking Water Act. Acceptable materials include:
23.6.3.2.1 copper alloys (including bronze or brass),
23.6.3.2.2 AISI Type 300 series, stainless steel,
23.6.3.2.3 nickel-copper alloy,
23.6.3.2.4 glass lined metal, and
23.6.3.2.5 plastic and rubber materials that comply with applicable National Sanitation Foundation standards and/or requirements of the Food andDrug Administration for potable water.

Notice which material is NOT in their list of acceptable materials?

 

[jungpeter]

Folks, this video by John over at Oxford Yacht Agency scares me a little as l consider how we can treat our water tanks to keep the water potable.

What should I be concerned about when adding a water sanitizing chemical, like a little bleach for example, to prevent contamination of our tank water?

Hi Bongi,

What always concerns me about routinely adding random amounts of (presumably household) bleach to aluminum water tanks is the likelihood of leaching out alloying elements contained in the tanks, forming "crusticles" of these elements on the tank walls and welds. Each of these sites is a potential leak site, leading to a water tank that works more like a sieve than a tank before long.

Typically, water tanks are routinely refilled from city water at your dock. Depending on your municipality, it's already treated with biocides similar to household bleach; thus, adding additional household bleach to your tanks only hastens your aluminum water tank's demise.

Unfortunately, use of household bleach in water tanks is a common and useful way to decontaminate not only the tank water, but the entire water system as well, superbly described by Ms. Peggi Hall in her book https://www.amazon.com/New-Get-Rid-Boat-Odors-ebook/dp/B01BW2ZSTW

So the conundrum is-decontaminate and maintain your water system, or protect your aluminum water tankage? Unfortunately, I have no solution to that conundrum, other than to minimize use of bleach, and/or replace your tankage with 316L stainless steel or rotomolded plastic.

Regards,

Pete

 

[Comodave]

If you replace them go with plastic. I like Ronko tanks.

 

[Bongi]

Thanks folks… I appreciate the valuable insights you shared here.

I have come to realize that Peggy brings a ton of wisdom on these topics!

I believe these tanks are black iron - like the fuel tanks of this era on these boats.

Would the same (or other) considerations need to be kept in mind for these?

 

[Comodave]

Try a magnet on the tanks, if they are steel it will stick.

 

[Old Sea Dog]

I will be removing the water tanks in our '79 36 later this month. Port tank leaks according to previous owner. I would prefer to install plastic tanks. I had several emails with John Shanahan a few months ago. Led me to the conclusion to tackle this myself. Looking for diagram and/or measurements for '70s era 36 water tanks.
Thanks.

 

[Bongi]

Finally got back to the boat and looked closely at the tanks. This was the label welded onto them.. we have aluminum tanks - and I guess all the caveats mentioned here about adding any chemicals to them now apply.

 

[slowgoesit]

As I stated on Old Sea Dog's thread, if you have access to the inside of the tanks, you can go in, clean up the inside surfaces thoroughly, and apply fiberglass cloth using food safe epoxy resin, readily available on the internet. Total cost per tank would probably be less than $200, not including your time. There is no need to cover inside baffles, as damage to them will not cause a leak to the outside.

The structure of the tank is still there, so what you are essentially doing is to build a "liner" inside of the old tank. The old tank provides the structure, and the "liner" provides the sealing. Once accomplished, the tank is probably good for another 50 years! And the advantage is you can treat the newly repaired tank with as much chlorine, or other treatments as you desire.

I've repaired black iron, SS, aluminum, and fiberglass tanks in this manner.

Best of luck in whatever you decide!

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