Put a zinc in aluminum holding tank

[sv_isara]

Hey all, my question is the same in the title.

My boat is well known for having an aluminum holding thank, that, when exposed to sea water, develops holes and leaks. Great. I was thinking about adding a zinc anode inside the tank. What do you all think? As long as I do a stout installation, it couldn't hurt. But would it help?

[peghall]

An anode won't hurt, but it won't help either because it's not galvanic corrosion that corrodes metal waste tanks, it's the sodium chloride in urine--which will prob'ly eat the anode too.


--Peggie

[sv_isara]

Originally Posted by peghall

An anode won't hurt, but it won't help either because it's not galvanic corrosion that corrodes metal waste tanks, it's the sodium chloride in urine--which will prob'ly eat the anode too.


--Peggie

Is there absolutely no chemical that can neutralize uric acid? Seems like there should be something I can put in the tank that will reduce the effects of uric acid

[peghall]

If there were, the medical community would be all over it. But it's NOT uric acid that "eats" metal, it's the sodium chloride. 10 years is the average lifespan of any metal waste tank and it doesn't matter how often you pump out and rinse out the tank. The first leaks usually occur at weld--a seam or a fitting while urine is gradually turning the bottom of the tank into a colander. When it became necessary to use holding tanks in the mid-late '80s, aluminum was the industry's choice because it was cheap. But by the mid '90s, seamless rotomolded polyethylene had become the recommended material. There are a number of mfrs and quality varies. The best quality tanks have thicker walls to support the 8.333 lbs/gallon that sewage and water weigh without flexing or bulging. Plastic tanks last as long as the boat lasts so you'll only have to do it once.


So do yourself a favor and replace the tank with a plastic tank before it starts to leak. Ronco Plastics Ronco Plastics marine Tanks is your best source. They make TOP quality thick-walled water and waste tanks for a very reasonable price and have more than 400 shapes and sizes, over 100 of which are non-rectangular, and they install fittings in the sizes and locations specified by the customer when they make the tank. There are retailers who sell Ronco tanks, but Ronco sells direct for a much lower price...and they're great to work with.

When looking at drawings it's important to know that there is no top or bottom until the fittings go in, and YOU decide where they go. So rotate, flip in any orientation to find the tank that fits your space.


--Peggie

[boat driver]

Originally Posted by sv_sharky

Hey all, my question is the same in the title.

My boat is well known for having an aluminum holding thank, that, when exposed to sea water, develops holes and leaks. Great. I was thinking about adding a zinc anode inside the tank. What do you all think? As long as I do a stout installation, it couldn't hurt. But would it help?

its not the salt water and corrosion , its the waste urine. \meanwhile, just to correct, you would need magnesium, as the zinc will not protect the aluminum.
surprised your tank is still in operation,

[Russ]

I believe aluminum tanks require magnesium anodes in any tank. I agree ain’t gonna help the poop. I have a 35 yo steel cutter with integral tanks that are sound. I believe he refers to cast iron vs cotton steel. But I agree plastic is nice

[grantmc]

Originally Posted by boat driver

... \meanwhile, just to correct, you would need magnesium, as the zinc will not protect the aluminum.
surprised your tank is still in operation,

That's what I thought too. Attaching a zinc self sacrificing anode to an aluminium tank seems counter intuitive to me. There's a difficulty obviously in knowing the purity of any of the metals in question.

And the reality is that aluminium is typically an alloy and there are a wide variety of types and grades, many of which have alloying elements of zinc, magnesium, copper and/or tin, not to exclude other compounds used in the smelting process such as silicon.

You'd have to ask the producer carefully worded questions too, before knowing the purity of the anode. Many are vitiated, and aluminium anodes in particular are usually described as 'alloy' anodes giving a hint to their origin. Cheaper 'aluminium' anodes in particular are often made by sources from the recycling industry. So the anodes they produce are of simply melted down junk. What you might describe as aluminium wheels, engine blocks, cans, pots and pans etc.

A huge consumer of such anodes is the fishing industry where they're attached to the pots. The operators are hardly likely to pay for premium product.