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Old 08-30-2016, 11:41 AM   #1
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Holding tank metal or plastic?

Falkor, our 1980 Cheer Men we just purchased, has a wasted disconnected holding tank approximately 30 - 40 gallons (guess). It is located in the bilge, forward of the engine, port of the center line, between stringers. (earlier post of mature plump people comes into play here)

I am enlisting help to remove and replace. The question, do I go back with a fabricated steel tank or plastic tank?
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Old 08-30-2016, 11:47 AM   #2
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Plastic!
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Old 08-30-2016, 11:48 AM   #3
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We replaced our 1985 Cheer Men stainless steel tank with a plastic one right after we bought the boat and boy was I glad we did as the lower port broke right off while trying to remove the hose. Really glad it was empty and clean at the time........
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Old 08-30-2016, 11:49 AM   #4
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Here is a source of rotomoulded tanks for you.
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Waste & Water Tanks | Ocean Link Inc
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Old 08-30-2016, 11:55 AM   #5
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Plastic is the choice here.
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Old 08-30-2016, 12:07 PM   #6
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Plastic! It is one of the few things on the boat that I've only replaced once.
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Old 08-30-2016, 12:11 PM   #7
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Plastic! It is one of the few things on the boat that I've only replaced once.
The whole idea of having to deal with a failed waste tank is pretty revolting!
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Old 08-30-2016, 12:15 PM   #8
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Plastic! Something we can all agree on!

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Old 08-30-2016, 01:37 PM   #9
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Seamless rotomolded plastic is the recommended material for waste holding...and your best source is Ronco Plastics (no relation to the VegoMatic Ronco). Ronco Plastics Marine Catalog They make TOP quality thick-walled (min. 3/8" for the smallest tanks, increasing in thickness at 40 gallons and above) water and waste tanks for a very reasonable price and have more than 400 shapes and sizes, over 100 of which are non-rectangular (which means you might be able to fit a larger one in the same space), and they install fittings in the sizes and locations specified by the customer when they make the tank. They do sell direct for a lot less than Plastics Mart and other retailers who sell Ronco.

Wall thickness is very important because unless the walls are strong enough to support the weight of the contents (water and waste weigh 8.33 lbs/gal), or fully supported on all four sides, the tank will bulge and flex which inevitably results in a cracked tank. I've seen tanks as thin as 3/16" which about the wall thickness of the tanks that Ocean Link sells (.20").
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Old 08-30-2016, 02:38 PM   #10
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Peggie


Thanks ...


I was hoping to touch base with you once the old tank is out and before installing the new tank to go over options with you.


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Old 08-30-2016, 04:29 PM   #11
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I'm always glad to help...You're welcome to contact me privately.
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Old 08-30-2016, 04:37 PM   #12
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HeadMistress.... You Rule! Do you have a book of your knowledge for purchase?

Well, I guess that was a rhetorical question. If you remove the smells the problems are solved!
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Old 08-30-2016, 04:40 PM   #13
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The book is money well spent!
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Old 08-30-2016, 04:45 PM   #14
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Polyethylene comes in different forms. Comparative thickness would be a good determinant as long as you are comparing like materials.

Cross-linked polyethylene could be considerably thinner than a linear low density polyethylene and achieve the same strength. Virgin material is quite a bit stronger than recycled material. Although I doubt anyone would be making one out of fully recycled stock.

Just like anything, always good to know what you are actually buying.

Ridges can add strength to a vertical wall too. Quite common on large rotomolded tanks.

FWIW, I put in a Sealand tank (LLDPE) and it was quite thick. I'd guess around 0.3125" on a pretty small 25ish gallon tank.
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Old 08-30-2016, 04:55 PM   #15
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HeadMistress.... You Rule! Do you have a book of your knowledge for purchase? Well, I guess that was a rhetorical question. If you remove the smells the problems are solved!
As a matter of fact I do...and although the title makes it seem to address only odor issues (my publisher thought "Get Rid of Boat Odors" would attract more buyers than "Flush With Success," which was what I wanted to call it), it's actually a comprehensive guide to marine sanitation systems and all the other sources of odor and aggravation. Available in both kindle and hard copy here:
http://www.amazon.com/New-Get-Rid-Bo...dp/1892399784/

Thanks for giving me the opportunity to post a shameless plug for it!
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Old 08-30-2016, 05:22 PM   #16
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Polyethylene comes in different forms. Comparative thickness would be a good determinant as long as you are comparing like materials.

Cross-linked polyethylene could be considerably thinner than a linear low density polyethylene and achieve the same strength. Virgin material is quite a bit stronger than recycled material. Although I doubt anyone would be making one out of fully recycled stock.
Just like anything, always good to know what you are actually buying.
Ridges can add strength to a vertical wall too. Quite common on large rotomolded tanks.
FWIW, I put in a Sealand tank (LLDPE) and it was quite thick. I'd guess around 0.3125" on a pretty small 25ish gallon tank.
With the possible exception of the occasional custom tank for an individual, all rotomolded water and waste tanks are linear LDPE (low density polyethylene). It's only necessary to use cross linked for fuel..it's the only type of PE that can be used for fuel. Linear would soak up petroleum and "melt." I don't think I've ever seen a rotomolded tank with ridges in the walls, but I won't say there aren't any.

There are a couple of mfrs of custom welded tanks who use PP because it's easier to cut and doesn't require seams to b heat and spin welded. Triple M Plastics in Maine Triple M Plastic Products Inc is one whose tanks are top quality. More expensive than rotomolded for which the mold already exists, but a lot cheaper than paying to have rotomolder make a mold for a one-off tank.

SeaLand tanks have always been overbuilt, which is not a bad thing...it's hard to go wrong erring on the side of caution. But it does drive the cost up. Ronco is actually the mfr for most of 'em...they make 'em to SeaLand's specs.
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Old 08-30-2016, 07:37 PM   #17
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Old 08-30-2016, 08:03 PM   #18
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My boat came with a plastic tank for blackwater. Steel for fuel and water tanks, however. Don't know why, but hope the decade-experienced boat builder knows what he's doing.
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Old 08-30-2016, 09:41 PM   #19
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A slight hijack,sorry ( my question probably doesn't justify a new thread). I have capped off my redundant long range fuel tank in the ER as being not required for our boat use and have been thinking about modifying it into a holding tank.

My ER is very tight and removing the tank would require removing the 7KVA gennie, which is a big job, so I am wondering if I can utilise the existing mild steel tank(about 30 years old)as a waste tank for the two heads on the boat.

Any observations on the above appreciated.

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Old 08-30-2016, 11:14 PM   #20
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"....so I am wondering if I can utilise the existing mild steel tank(about 30 years old)as a waste tank for the two heads on the boat."

Unless you want to replace it within 2-5 years, I wouldn't. The engine room is a horrible place for a waste tank anyway. We can find another much better location that provides much easier access. And I have a Skype account.
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