Plywood water tanks?

[Capt. Mike]

The stainless steel fresh water tanks on our CT42 sailboat have rusted through. Cost is a factor in replacing them. What are the opinions regarding building the replacement tanks out of encapsulated marine grade plywood? I would first use CPS to protect as well as possible before building a thick coat of RAKA epoxy. Each part would be encapsulated before assembling the tank.

Thanks,
Capt. Mike

[Richard Hillsid]

How much are they asking for new stainless tanks?

[Capt. Mike]

I have not checked the price of stainless tanks, but I have checked the price for plastic ones. The pair of plastic tanks is about $500. I believe stainless tanks would be custom fabricated and more expensive. The plastic tanks come in a variety of shapes, but none are the same. Therefore to get the plastic tanks to fit the available space I would have to give up some storage capacity. If I build the tanks out of plywood, I can make them the same shape and have the same capacity.

Capt. Mike

[lewisboats]

You would have to build them heavy as they will have to contain quite a weight of water (62.4 lbs/cu ft or about 8 gals), even using CPES you will only penetrate the depth of the first layer of wood, the core plys won't have any plastic in them. You will need to put more than one coat of epoxy on the plywood and I would recommend a layer or two of glass too. Your tanks will be heavy compared to SS or Plastic...no 1/4" here. I would say 1/2"-3/4" plus some bracing too, depending on the size of the tanks.

But that is just my opinion

Steve

[timgoz]

Mild steel tanks, epoxy coated (inside & out) would be effective & inexpensive. No strength issues would arise with such tanks if baffeled and built properly.

They would also be very repairable.

Take care.

TGoz

[D'ARTOIS]

Yes, that is a very good option. Make sure that the coating for the inside is chemical resistant as drinking water is mostly chlorinated.

[hansp77]

Ever the cheap scavenger/salvager...
I have a few thoughts and questions.

Try some of your local metal salvagers/reclyclers. Sitting in their yard may just be the exact tank (or something easily altered to) that you are after, and could be very very cheap.

Aside from that, another thought occured.
One afternoon I was working on my boat in the yards and thought that I needed some light stainless brackets. We went to the hardware store open and they only had galvanised.
On the way back, the suburb I was in was having hard rubbish collection, so I stopped and picked up a nice stainless kitchen sink (these things are ALWAYS getting thrown out like this)
With my grinder I cut off some strips and panels to make into brackets. (I ended up changing plan and not using them though)

If the size was anything like appropriate, couldn't one just cut out two sinks, and seal/rivet/weld them upside down on top on one another? a simple plumbing attachment on the bottom would seal it (and allow for easy draining) and the plug hole on the top would be ready made to screw piping onto.
I am not sure if it is the right stainless for a water tank,
or if DIY stick welding would produce a sufficient weld.

Shoot away...

Hans.

[LP]

Didn't they use to solder copper sheet into tanks?

[Tim B]

The Gougeon brothers have built plywood water tanks in the past, with great sucess. I suggest you use thier book on boat construction as a starting point.

Tim B.

[stevel]

My dad made the freshwater, greywater, and blackwater tanks for his bus conversion out of cheap ply, and they were still leak free and rot free when I sold off his bus 17 years later. I'm not sure if they are your best option weight-wise, but if you need inexpensive custom tanks, they are a workable option. He glassed his inside, and then painted the inside of the freshwater tank with an epoxy to avoid the taste that resin puts into the water. I can't remember if he glassed the outside, or just resined it.

[Ari]

How many liters is the tank size? I had seen this kind of construction before. The tank do last very long if built properly but the weight.if it is thick.. very heavy. The one that I saw is for inter island fresh water supply boat, 50 tonne capacity. Normally for small size, about 300 litres tank I used HDPE -plastic tank. If you have Japanese koi fish pond liner, that also can be used to line your plywood tank. Very long lasting this liner and doesn't leech out hazardous chemicals into the water.

[Verytricky]

Hi,

Some cheap scates in the marine fish world build plywood tanks for their fish, to avoid the costs involved with the very large glass tanks. Look at a fish website like reefs.org or garf.com for plans.

These tanks are up to 500 gals, and keep delicate corals and fish, so will store drinking water..

[Capt. Mike]

Thanks for all the replies. The capacity of the water tanks I will replace is about 60 gallons each so I don't think they will be too heavy. I built diesel fuel tanks with plywood several years ago. Before doing so I wrote to The Gougeon brothers to see if it was practical. They sent me a 10 page paper about building tanks of plywood. Their recommendation is to apply seven coats of epoxy to the interior and to use a little less hardener than normal to be sure all of the hardener is consumed to avoid having the coating be pourous. I tabbed all the seams and coated the interior per the paper and the tanks have worked well. I was wondering if anyone had used a similar method for fresh water tanks and if there is any impact on the taste or quality of the water. By the way the diesel tanks are still in service and have no problems.

Mike

[Ari]

Originally Posted by Capt. Mike

I was wondering if anyone had used a similar method for fresh water tanks and if there is any impact on the taste or quality of the water. By the way the diesel tanks are still in service and have no problems.

Mike

My house fresh water tank are made of fiberglass and epoxy resin, it had lasted 10 years before started to leak at high stress point area.I cannot confirm the quality of water since it is not tested but on the the smell,the water is odorless. Our housing board rules doesn't allowed water supply for the kitchen to be routed to any storage tank. It must come from a direct line from the main supply pipe.

[Verytricky]

Really - people are keeping corals in these tanks, and corals die if you look at them funny. So the tanks have to be perfect.