Holding tank thickness

PascalG

PascalG

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planning the tankage for the 26' sloop i'm building...

i see Todd makes 2 type of tanks, 1/4" or 5/16" wall. i'm having issues fitting the thicker wall tank in the boat since they are at least 24" long. I'm considering the standard 1/4" wall tank instead, which i understand may be more prone to permeation but since the tank will be installed under the cockpit floor, odors will not get in the cabin. And at under $100 for the 9usg, it's cheap to replace after a few years.

am i asking for trouble?
 
Pascal, I'm certainly not an expert but here's a link i read about boat building a while ago. Also posted the key paragraph.
Keith

Rotationally molded seamless polyethylene with a minimum wall thickness of 1/4" for the smallest tank is the material of choice. Holding tanks are made from linear, not cross-linked (as fuel tanks must be) polyethylene; therefore anything thinner than a 1/4" wall will permeate—and that must increase proportionately with the size of the tank walls—i.e., a 30-gallon tank should have a wall thickness of 0.375". Furthermore, if the wall thickness doesn’t continue to increase with size, the tank walls will be too weak to support the 8.333 pounds per gallon that sewage weighs (meaning a 40-gallon tank must support 333 pounds); it will bulge and, at the very least, distort and create leaks at the fittings--if it doesn’t actually crack. There are poly tanks being sold as holding tanks through most of the marine catalogs which have maximum 1/4" walls. People buy them because of price and out of ignorance. We recommend against them, and strongly urge that you spend the extra money to do it right the first time by installing top quality tank that will last 20 years or longer.

http://www.boatbuilding.com/article.php/MarineSanitationFactvsFolklore
 
I was just reading about holding tanks in Practical Sailor. Do you subscribe?

One point that was brought up was that permeation isn't a big deal if the right additives are used (they recommended Odorloss and the cheaper, similar Camco product) and the tank has adequate ventilation. If all you're growing in there are aerobic bacteria, there will be no smell to permeate. I think a 1.5" vent line was the minimum.
 
If you have easy access to replace it, the boat will not take a pounding, I don't see why it will be a problem.
 
As I recall Peggie always recommended the thicker walled tanks. And two big vent lines of course.
 
Interesting in the article was that a cheap aquarium pump could help where a larger vent line wasn't installed. I had actually done that for years with great success. I'd still be doing it but all those pumps are AC and now with my solar panel I'm not running the generator as much. I doubt Pascal wants to put a generator on the sloop, I just found it interesting. Two vent lines are of course a better idea.
 
I talked with Peggie about the cheap aquarium pump idea. And you have to make sure the pump can really put out the proper volume of air based on your tank size.
 
You describe the boat as a day boat. How much are you using the head for #2? Anchoring for a 3 day weekend or just for day sails.....

If space is that tight, I don't see a big issue as this boat is not a live aboard and you have the ability to pump out and flush the tank out easily since it is only 9 gallons.
 
Get the 1/4. After a couple of years it will be thick walled anyway
badteeth.gif
 
Daysailing mostly, maybe the occasional overnight in winter when it a cool

Going to go for the 1/4", weight and bulging won't be an issue with such a small tank
 
quote:
Originally posted by Capt. Bill1

I talked with Peggie about the cheap aquarium pump idea. And you have to make sure the pump can really put out the proper volume of air based on your tank size.
Click to expand...


I bought a 30-gallon pump for a 20-gallon tank. It worked great for 3 years until I put the larger vent line in. It wasn't a bad $20 experiment :-)

"20-gallon tank" - now you know why I have a Type I MSD!
 
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