Base board support for holding tank

[Skipper]

Hi,

I have an infinitesimal holding tank - 3 gal. The hilarity is that the builder installed the vent 2\3 of the way up the tank, so you can only fill it 2\3 (2 gal) before the pressure from the head sends liquid out the vent topside. What's more insane is that the tank only empties to 1\3, leaving a gallon in the bottom, because the deck pumpout starts sucking air when the level reaches the 1 1\2" hose outlet in the tank.

Therefore, the capacity is actually 1 gallon. IE: utterly useless.

Anyway, there is more room in the holding tank space, so I measured for and then purchased a new 5 gallon tank with the vent in the proper location. Still tiny, but actually usable.

The old tank has a composite board under it, between it and the ply bottom of the cabinet. The board is 3\4", black, and looks like foam but it's as solid as ply. The top has a vinyl(ish) layer that is rough in texture. I'm guessing the board is there to ensure proper support for all areas of the tank bottom, and the rough top for additional grip to enhance the tie-downs.

So, the new tank is bigger, which means I need a bigger board. Can anyone guess as to what type of board this is? I can't find anything like it. Or, a suitable alternative.

Thank you

 

[TLW]

Sounds to me like "pontoon boat decking." Not sure what its industrial name is, but know it was obtainable when I was in the boating business. I would check with pontoon boat dealer. I know it was available in 4 x 8 sheets. It is basically a wood (I think) product sheet with a veneer ply of rubber-like material.

 

[Ralph Johnstone]

Perhaps the Owner ..............................

Therefore, the capacity is actually 1 gallon. IE: utterly useless.

.................. was required to have TB in order to purchase the boat. That's TB as in tiny bladder.

But that aside, any chance you could use 3/4" ply and then top it off with 1/4" closed cell foam ? Perhaps with a bit of adhesive between the ply and the foam. That's if you're really concerned with every square inch of the holding tank being supported by the ply.

If it's a well made poly tank, the foam may be a bit of overkill. With the tie down and a few border pieces around the tank, it should be as solid as a brick s_ _ t house even without the foam in between.

Good luck with the project and I'm sure everyone's bladder is relieved .

 

[Steve Dion]

for a 5 gal tank, wouldn't you be better off with a porta-potti that has a pump out? Some of these are 6 gals.

Check out Ronco Plastics. They have some tanks that you could mount in the v of the hull. Put foam under it and glass in some wood to secure the tank in place.

I am guessing that you can get at least 10 gals. 5 gals is probably only 2 6 packs for 2 people. Going to be short weekends!:dance::dance:

 

[higgs]

Figure about 50 lbs weight for your full head tank. Would the 3/4" board you have support that?

 

[Skipper]

Thank you, all.

The tank must be supported at all areas. Any overhang, especially inside the edges where the walls are not supported, would result in the full weight of the tank pressing on only the strength of the individual polymer, not the strength of the box structure.

I'm not changing to a porta pottie. The boat is already built with the hoses routed, raw water intake, deck pumpout, y-valve, direct OB thru-hull, a brand new Raritan head, etc., and now a new tank in inventory for installation. Also, a macerator is planned. It's a fabulous setup, except for the strange tank. All I need is a bigger, better-vented tank.

I think I might have to use marine ply as suggested. For space reasons regarding the curvature of the bow, I can't put the tank directly on the cabinet ply. This brings me to the next question: Where can I find just 20" x 10" of 3\4" marine ply? I guess I'll hunt the internet.

Thanks again

 

[Steve Dion]

You can figure out your gallons by determining the size of the tank and dividing by 231 cu in = 1 gal.

 

[Ross]

For a bit of reference how thick are you companion steps and how much do you weigh? A fifty pound tank? A small child is that heavy.