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From: (no name) (no email)
Date: Mon Sep 24 2001 - 08:41:44 EDT
Hi, Margie, in order to make maximum use of the oddly shaped space I had
available, I built my own holding tank. I used 1/4" (non-marine) plywood,
epoxy, and 6 or 7.5 oz glass cloth. I built it in early 1997 and have had no
problems; it has a capacity of about 30 gallons.
Originally, I only put glass on the inside and just coated the outside with
epoxy. This year I noticed that the epoxy on the outside had cracked in many
places, as un-reinforced epoxy on wood has a tenancy to do. Since I'm
teaching my girlfriend to do glass work, I had her cover the outside with a
layer of 6oz as a learning project. The tank has a vent fitting near the top
of one side, a beckson screw-out inspection port on top, and a single heavy
duty input/output fitting. The tank wall is reinforced where the fitting
goes through with a layer of heavy roving on the outside and a 1/4" backing
block on the inside. I used a single fitting which is connected to a
Y-valve, which allows the tank to be connected to the head or to the pumpout
plumbing (there is a short length of hose attached to the fitting on the
inside that runs to the bottom of the tank-- a baffle holds the hose in
place).
I marked off the plywood pieces on a sheet of plywood and then glassed over
them before cutting. This is easier, but you may want to consider running
some glass tape along the seams after assembly for extra strength -- I did
not and have had no problems, though. After cutting my pieces, I tacked them
together with small nails and glued them with epoxy thickened with colloidal
silica -- using fillets along all inside corners.
Suggestions/things I would do differently: I used a vent fitting for 3/4" ID
hose (I think). I suggest using a vent fitting and hose of the same size as
your other plumbing (usually around 1.5"ID). The main input fitting (like a
through hull but with hose barbs on both sides) was hard to come by and not
cheap -- figure out and get your fittings first. The bottom of my tank has
sump, about 1' square and coming down about 6-8 inches below the bottom of
the tank. This fits well with the shape of my boat as it gets narrower down
low in the bilge and gives me a little extra capacity. The main advantage is
that my pickup hose is down in this sump and it allows me to pump out almost
everything -- there's only about a pint that can't be pumped out, which is
much better than other tanks I've seen without a sump.
Oh, and if you're thinking of doing this to save money.....think again if you
assign any value to your time :-)
Let me know if I overlooked anything or if you have any questions.
JP
In a message dated 9/24/01 1:11:03 AM Eastern Daylight Time,
writes:
<< Hallo all,
My husband is planning to build a holding tank in our wooden boat (H28). Has
anybody had experience doing this themselves, and could offer any tips?
He has read an article saying you can build one using plywood coated with
epoxy resin, with internal baffles. The only place to put it will be under
the forward V-berth. Holding tanks are not common where we live, but will be
required as we go further up the Australian coast.
cheers, Margie
>>
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