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Old 13-06-2008, 20:51   #1
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Holding tanks

I'm looking to upgrade my holding tank from 6 gal to 20-40 gal, but the only space available is about 24 inches wide x 18 x 36 high. Can a custom
tank be made out of Stainless or aluminum? My instinks ( sorry ) say stick to plastics? Any suggestions?
thanks
Brad
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Old 13-06-2008, 21:13   #2
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Plastics do well and there are places that can build a custom plastic tank to order with inlets and outlets done to your specs. My neighbor who is quite cheap to the extreme thought is was a fair deal. I should get the details and post it as they can do a very custom job if you can work the math and spcecify what you really need. That includes computing if you can get it installed too. They ship itm to you and you are on your own. Alumininum would be a very poor choice. Stainless is more expensive and does fine. Human waste is not the most gentle stuff to haul around. The plastics do a fair job and your instinct was probaly good, though after about 15 years the stink eats through almost anything including the hose. You probably know what bad hose is like by now.
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Old 13-06-2008, 21:44   #3
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Epoxy/Fiberglass is a viable alternative and might be cheaper to fabricate in a custom shape than a molded plastic. If built well it can go a very good job, built badly, they can stink (literally and figuatively)

I built mine by making a mold out of styrofoam, making sure it fit, then laying the fiberglass epoxy over it. When you cut the holes for the fitting, you pour in a half liter of acetone or gasoline, and the foam dissolves and pours out.

Bill
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Old 14-06-2008, 16:10   #4
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I built mine using plywood, then epoxy-sealed, epoxy primed, and LPU paint INSIDE AND OUTSIDE. Use plastic through hulls for fill, drain and vent hoses, PVC pipe if you need a pickup, but a bottom drain is simpler. Don't forget an inspection, cleanout port, well sealed.
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Old 14-06-2008, 17:49   #5
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Was talking to a boat builder recently who does timber/grp composite boats (my interest was sparked because it will be a major to get our ss one out if it starts leaking ).

He reckoned the cheapest, easiest and best (so can't do better than that ) is just fabricate from ply, epoxy saturated and fibreglass lined on the inside. Can also be built in situ if space or access is tight.
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Old 15-06-2008, 01:58   #6
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The P.O. on my boat built one out of 10 in.dia. white poly pipe sched 40. End caps and stuff is available and everything glues up with pvc glue. Cheap to build. Hangers made from SS flat bar. I was going to replace it with a new tank that had all the bells and whistles on it but having used it for awhile I figured its working out good why replace it. Capacity about 25 Imp. Gal.
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Old 15-06-2008, 02:39   #7
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Originally Posted by Lancerbye View Post
The P.O. on my boat built one out of 10 in.dia. white poly pipe sched 40...
Capacity about 25 Imp. Gal.
I'd be tempted to use a larger diameter pipe, as a 10" internal diameter pipe, holding 25 gallons, would have to be over 6 feet (74") long.
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Old 15-06-2008, 03:09   #8
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Sorry my mistake it's 12 in. dia white pipe. was put in, in two equal lenght sections of 30 in.
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Old 15-06-2008, 04:19   #9
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A 12" I.D. Pipe holds about 0.485 gallons per inch, so your (2) 30" sections should hold over 29 gallons.

How do you know when you're approaching "full"?
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Old 15-06-2008, 04:34   #10
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I have a tank tender line going to it so we have a rough idea as to the level.I will soon be installing a high level alarm in it that also shuts off the vaccum pump. Because sometimes someone forgets to watch the Tank Tender. That results in a mess to clean up in the lazarette and a ruined odor filter. Don't ask me how I know this. Those bloody filters are expensive. The one problem with the Tank Tender is that the back pressure developed varies with the density of the material. This is not constant in a holding tank.
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Old 15-06-2008, 06:31   #11
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Holding tank replacement

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Originally Posted by bmartinsen View Post
I'm looking to upgrade my holding tank from 6 gal to 20-40 gal, but the only space available is about 24 inches wide x 18 x 36 high. Can a custom
tank be made out of Stainless or aluminum? My instinks ( sorry ) say stick to plastics? Any suggestions?
thanks
Brad
Brad, I had the job of fitting a holding tank to my boat, which is a 1975 era CHB 34, and definitely not designed to have one. The issue like yours was where and how big, and what type would work? I managed to fit a 105 litre Turtle Pack bladder type under the for'd engine room floor, in a space similar to yours, nestled in the bilge effectively, inside a cradle of 4 thicknesses of polythene, then carpet, (with 2 inch PVC pipe under it to allow bilge drainage for'd to the bilge pump area, and made the engine room floor so it was supported on four strong brackets in such a way it can rise when the tank is getting near full. Might sound a bit weird, but it works, and the rising floor is my sign to have it pumped out - or to empty in open waters if able, via TMC macerator pump nearby , with a lockable Y-valve to divert to deck or thru-hull outlet. One advantage of the collapsible bladder type of tank is there is no danger of it imploding on pump-out, or blowing back up the line when pumping to it, even if your exhaust vent gets blocked, because it expands and contracts according to the volume, however, you do need to have a vent to the outside as with all such tanks. I plumbed mine into the least used bilge pump thru-hull, near the hull, and with a non-return valve just downstream of it in the bilge outlet, as you do not want the gases seeping into the bilge. However, if the vent blocks, a gentle puff from a dinghy pump down the outlet via the thru-hull from outside, clears it beautifully easily - albeit with some rather smelly gurgles. All the same, if I could have got my hands round the neck of the bureaucrats who brought that particular law in without realizing just how hard it would be to comply in some vessels.............must be the worst job ever....getting that sanitation hose onto the barbs, let alone off again...... heating it with a hairdryer did help somewhat, but what a job......I should add I'm speaking of Australian waters here - those regs have been in place longer in other parts like the US, I know. Still not a pleasant job, whereever....Happy holding tanking......it's all meant to be fun.
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Old 15-06-2008, 07:05   #12
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"However, if the vent blocks, a gentle puff from a dinghy pump down the outlet via the thru-hull from outside, clears it beautifully easily"

This is why I love this forum - beautiful idea! Thanks.
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Old 16-06-2008, 20:37   #13
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Thanks to everyone, lots of great ideals. I think I'm going to look into the
sch. 40 pipe ideal of LancerBye. Here in the Cayman's the pipe would be easiest to find parts for. I'm thinking of 2 mounted vertically side by side.
LancerBye is this how yours was?
Brad
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Old 16-06-2008, 20:56   #14
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The PO glued two 30 in sections together and mounted them horizontally, I think there is a baffle in the middle. Personally I think vertically mounted would have been better, but not enough depth in the lazerette.
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Old 17-06-2008, 04:49   #15
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FWIW: The thicker Schedule 80 pipe will be stronger than Schedule 40, and may be less permeable to odour, over time - though I don't think this should be much of an issue.
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