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Holding Tank Installation


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#1 QLite

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Posted 16 March 2012 - 01:43 AM

I'm installing a 25 gal roto-molded Ronco holding tank in the v-berth area, just forward of the aft most bulkhead. The tank has been made to somewhat follow the shape of the hull. So as to evenly support the 200 or so possible pounds that the tank may weigh when full, I'm thinking of placing the tank where I want it and then spraying the 1"+ Great Stuff expanding closed cell foam all around the underside of the tank. Additionally, so as to not 'glue' the tank and foam to the hull I'm thinking of first laying down some mylar (aka 6 mil visquene) or large 30 gal style trash bags so as to create a mold release. I'd also tape this same plastic to the tank. After the foam has cured, I hope to lift out the tank and remove the foam plug mold and the hull lined plastic. Then I'll cut away where I need to for my outlet hose in the mold plug and just set the mold plug back into the hull. Then I'd install the tank with an aluminum flat bar bracket holding the tank to the bulkhead.

I've sprayed some of the Great Stuff onto different plastics including a piece of wood coated with PVA on a part and vaseline on another part. The Great Stuff released pretty easily from the mylar and garbage bag there best, next best was the vaseline (will make a mess).

What does everyone think of this idea? If / when, some water or effluent gets in and or around the foam will it cause Mould and will I be able to clean it up? It seems to me, that having a uniform light weight mold is far better than some marine ply or heavy fiberglass matting. I expect the thickest (depth) of required foam would be about 4-5".

Thanks in advance for any suggestions or constructive thoughts.

Attached is a rendering of the hull section and tank used for fitting purposes.

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#2 Innocent Bystander

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Posted 16 March 2012 - 11:01 AM

I'm installing a 25 gal roto-molded Ronco holding tank in the v-berth area, just forward of the aft most bulkhead. The tank has been made to somewhat follow the shape of the hull. So as to evenly support the 200 or so possible pounds that the tank may weigh when full, I'm thinking of placing the tank where I want it and then spraying the 1"+ Great Stuff expanding closed cell foam all around the underside of the tank. Additionally, so as to not 'glue' the tank and foam to the hull I'm thinking of first laying down some mylar (aka 6 mil visquene) or large 30 gal style trash bags so as to create a mold release. I'd also tape this same plastic to the tank. After the foam has cured, I hope to lift out the tank and remove the foam plug mold and the hull lined plastic. Then I'll cut away where I need to for my outlet hose in the mold plug and just set the mold plug back into the hull. Then I'd install the tank with an aluminum flat bar bracket holding the tank to the bulkhead.

I've sprayed some of the Great Stuff onto different plastics including a piece of wood coated with PVA on a part and vaseline on another part. The Great Stuff released pretty easily from the mylar and garbage bag there best, next best was the vaseline (will make a mess).

What does everyone think of this idea? If / when, some water or effluent gets in and or around the foam will it cause Mould and will I be able to clean it up? It seems to me, that having a uniform light weight mold is far better than some marine ply or heavy fiberglass matting. I expect the thickest (depth) of required foam would be about 4-5".

Thanks in advance for any suggestions or constructive thoughts.

Attached is a rendering of the hull section and tank used for fitting purposes.



The foam idea in interesting but it will soak up anything that gets on it. I'd go for a shelf that conforms to the bottom of the tank, sealed with epoxy and allows airflow around and under the tank.

#3 Dick Ishuge

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Posted 16 March 2012 - 11:56 AM

You might want to switch to the black pond foam version of greatstuff. A little better w water immersion :-)

#4 TPG

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Posted 17 March 2012 - 12:39 PM

http://www.uscomposites.com/foam.html
4lb density is whats used to support fueltanks in ALOT of boats.

#5 slap drone

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Posted 17 March 2012 - 09:25 PM

my $0.02 worth ...

no matter what solution you have for a holding tank bed, make sure that all your plumbing joints are accessible, that the tank is straight forward to remove and clean the underside and that the the bedding has zero porosity.

nothing can be finer - than poopy water in the liner - of my holding tank at 2am in the, ...morrrnin'

SD

#6 QLite

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Posted 20 March 2012 - 03:19 AM

Thanks for the great feedback.
I've ordered the 4 lb density foam from USComposites. After removing and carving the mold plug I will apply a coat or two of West Epoxy to the entire plug. I'll also leave a void area under the plug if / when any moisture develops. Hopefully, this installation will go pretty easily.

#7 Ryley

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Posted 20 March 2012 - 11:30 PM

Thanks for the great feedback.
I've ordered the 4 lb density foam from USComposites. After removing and carving the mold plug I will apply a coat or two of West Epoxy to the entire plug. I'll also leave a void area under the plug if / when any moisture develops. Hopefully, this installation will go pretty easily.


It would have, had you not actually said this out loud. The head gods are fickle and easily offended.

#8 -Julian-

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Posted 21 March 2012 - 04:16 AM

Thanks for the great feedback.
I've ordered the 4 lb density foam from USComposites. After removing and carving the mold plug I will apply a coat or two of West Epoxy to the entire plug. I'll also leave a void area under the plug if / when any moisture develops. Hopefully, this installation will go pretty easily.


Good call sealing the foam with epoxy.

#9 Kirwan

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Posted 22 March 2012 - 12:17 AM

Couple of points:

The foam expands pretty aggressively - be careful it doesn't lift the tank. Think ahead about hold-downs, and maybe do the foaming with the tank full of water.

Most foams are rigid and brittle - that is, they dent, crush and crumble easily. otoh, The stuff referenced is probably better than average.

Some foams form a nice skin - I'd experiment with your mold release agents to make sure they don't mess this up. (but still coat it afterwards - note, some foams and some chemicals don't play well together)

For this reason, I'd try to 'form' some of the extra features as part of the foaming, rather than carve them in later. For example, lay a pipe or board down below the foam so that it forms a drainage channel. Heck, you could make your channel forms out of clay, and just remove later.

I'd still include some *other* supports that are strong enough to support the tank, but that's me.

#10 QLite

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Posted 22 March 2012 - 12:59 AM

Kirwan, good points. I am planning on (2) 1-1/4" x 3/16" aluminum bar stock braces which will hold the tank to the bulkhead as well as something to hold it down when healing, etc.
I'm also planning on laying down some PVC halves of pipe for a drainage cavity. I'll wrap the hull area including the drainage PVC area with slippery plastic as a mold release. I'll likely integrate other areas under this mold release plastic as well. Maybe I can work my outlet hose area and fitting into this as well. I've been considering clay to help create the unique required forms.
Thanks.

Couple of points:

The foam expands pretty aggressively - be careful it doesn't lift the tank. Think ahead about hold-downs, and maybe do the foaming with the tank full of water.

Most foams are rigid and brittle - that is, they dent, crush and crumble easily. otoh, The stuff referenced is probably better than average.

Some foams form a nice skin - I'd experiment with your mold release agents to make sure they don't mess this up. (but still coat it afterwards - note, some foams and some chemicals don't play well together)

For this reason, I'd try to 'form' some of the extra features as part of the foaming, rather than carve them in later. For example, lay a pipe or board down below the foam so that it forms a drainage channel. Heck, you could make your channel forms out of clay, and just remove later.

I'd still include some *other* supports that are strong enough to support the tank, but that's me.



#11 bop11

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Posted 10 April 2012 - 08:07 PM

You sure you want 200 pounds of ballast acting way out there? Maybe rethink to center the tank front to back rather than across so the torque arm is significantly reduced. That weight subtracts from the righting moment and will significantly increase heel. When the tank is half full, on one beat, the top fittings will be below the sewage surface.
Also those joints right under the berth, I'm glad I won't be sleeping there.

#12 TPG

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Posted 11 April 2012 - 12:08 AM

The foam expands pretty aggressively - be careful it doesn't lift the tank. Think ahead about hold-downs, and maybe do the foaming with the tank full of water.


Few points past this.
This stuff expands tenaciously. I installed 2 40 gallon fuel tanks with this stuff, I premade my tie down brackets and they had to go in before the tank was in. And the tanks STILL had to have extra hold downs as this stuff expanded.

Also you will get it everywhere and anywhere, make sure to cover anything you love with plastic, or it will be foamed.

use 2 of the quart home depot plastic paint things for measuring it, another 10 for mixing it, ie: measure, pour both into big container, mix like mad, pour, chuck mixed container as it expands rapidly. wash rinse repeat.

I wouldn't foam the tank full as you want to fully encase under and around.

#13 Ishmael

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Posted 11 April 2012 - 03:13 AM

Fill the tank with foam and move to Canada. You can pump out shit anywhere here. Especially Ottawa.

#14 Willy T

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Posted 11 April 2012 - 03:29 AM

Whats te deal with odors under the v berth. Im loooking at something similar in the power baot i stead of a portapotty. Dont really want either though




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