Raw water & aluminum holding tank

Just realized we have raw water intake for the two heads and an aluminum holding tank. Not sure what will happen when vessel is in saltwater, drawing salt water into head and waste holding tank that is aluminum. Any help is great.

Aluminum does not get along with uric acid and has a shorter life span than any other material commonly used in fresh water..... Salt and uric acid together = a very short life span.

How short ? depends on the acidity of your urine.

temple1120 said:

Just realized we have raw water intake for the two heads and an aluminum holding tank. Not sure what will happen when vessel is in saltwater, drawing salt water into head and waste holding tank that is aluminum. Any help is great.

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You could convert the head to fresh water, use a lot of fresh water to delute, added baking soda, and/or pump the tank often.

Phil Fill said:

You could convert the head to fresh water, use a lot of fresh water to delute, added baking soda, and/or pump the tank often.

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That would hel a dock queen but using up fresh water to flush while cruising is a time consuming and sometimes expensive proposition.

boatpoker said:

That would hel a dock queen but using up fresh water to flush while cruising is a time consuming and sometimes expensive proposition.

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He asked for some help! Other than replacing the tank, the other is to make it last. One of the first things we did was convert the head to fresh water, as I have thing about through hulls! Took out the through hulls below the water line except the 671 and gen set in take. When at dock they are closed. We are defiantly Dock Queens as 99.99% of the time we are at the dock and get pump every week.

There are many Al hulled boats in salt water and they don't come to grief. The tank contents and potentially non-compatible connectors may or may not cause problems. Keep an eye on things and be prepared ( how to do it and with what tank) to change the tank out but until problems crop up I'd not worry. Who knows, it may outlast the boat!

Fresh water flushing advantages are well known, but your Al tank won't know the difference.

If I recall correctly, Peggie Hall, who wrote the book on marine sanitation, really doesn't like metal holding tanks and I think aluminum is the worst. Sewage, whether mixed with salt or fresh water, is pretty corrosive. I think you'll have leaks probably sooner rather than later. If you can get the old tank out, it's not very expensive to buy a good plastic tank.
Ronco Plastics makes about 500 different sizes and shapes of heavy wall tanks. I bet they'd have something that would work.
Here is a link.
Ronco Plastics - Marine Water Tanks, RV Water Tank, Auto Detail Tanks, Water Tanks

I wouldn't wait until the aluminum tank leaks. That can get nasty.

I was reading a thread on Cruisers Forum about a 43 year old Al holding tank and the owners concerns. Peggy came back and told him the standard, "Al will only last 2 to 5 years." I believe Browards have Al integral tanks, wonder how they are holding up on the 25 year old vessels.

Of course, Al is not the product of choice and hopefully Temple 1120 will make it through the end of this season. How old is the tank Temple and how has the boat and tank been laid up in the winter months?

"but using up fresh water to flush while cruising is a time consuming and sometimes expensive proposition."

Not that bad as boat toilets do not use 6gal or even 1 1/2 gal per flush.

A Sealand RV unit uses about a cup per flush .

Most marine toilets are in the shower area , so the spray can be used instead of boat re-plumbing, automatic vacuum breaker with hand spray.

sunchaser said:

I was reading a thread on Cruisers Forum about a 43 year old Al holding tank and the owners concerns. Peggy came back and told him the standard, "Al will only last 2 to 5 years." I believe Browards have Al integral tanks, wonder how they are holding up on the 25 year old vessels.

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Many, if not most, AL boats over a few meters in length use integral AL tanks for blackwater and they hold up fine as long as the fittings are galvanically compatible and the alloy is a 3 or 5000 series, and they are not made of thin sheet metal. Even some 6000 alloys perform satisfactorily in some installations. Older tanks may have pitting corrosion under the scum line and sludge but regular flushing will reduce that to a minimum.

RickB said:

Many, if not most, AL boats over a few meters in length use integral AL tanks for blackwater and they hold up fine as long as the fittings are galvanically compatible and the alloy is a 3 or 5000 series, and they are not made of thin sheet metal. Even some 6000 alloys perform satisfactorily in some installations. Older tanks may have pitting corrosion under the scum line and sludge but regular flushing will reduce that to a minimum.

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And there you have it

sunchaser said:

And there you have it

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Just did a bunch of work on a 1983 built AL boat with AL blackwater tanks and piping. The only issue was where bronze valves were threaded onto AL nipples at a couple of flanges.

According to the galvanic table 3 or 5000 aluminum is rated a little less than mild steel. Aluminum boats would tend to have aluminum tanks as other metal might cause a galvanic reaction. Aluminum boats are zinced as most boats are, and have a protective barrier/bottom paint. Are the tanks connected to the zinc loop? The Eagles 32 year old fuel, mild steel, and the water, SS, are connected to the main zinc loop.

It sounds like the boat is on fresh water? If so then connect to the boat domestic fresh water may not be important. We use a lot of fresh water to dilute, also once a week the lines are flushed clean with fresh water the morning the tank are going to be pumped out. .

I did replace the holding tank as the original one was to small, not in that great of shape and replace the hoses at that time. The hoses have lasted 10+ year with no odor/weeping. Also when the time comes it should not be as messy smelly. I would due some preventive action to make the hose and tanks last longer.