Water tanks - install - tricky questions here...

[CanuckSailor]

Hello all - I have bladders under my cockpit benches and I've decided I'm not happy with them. I was planning on removing the bags, glassing the interior of the space and sealing it off with piping as needed.
Then I came across a suggestion that food grade plastic is 'weldable', and that one can build tanks from it - a far less messy job than using fibreglass. I'm researching the possibilities and wonder if anyone here has experience with this technique? My thinking is to place the plastic sheets in the space now occupied by the bladder, which is wood on three sides, the inner hull on the fourth and bottom, and then place a sheet overtop with inspection plates, and the appropriate fittings.
Looking for your thoughts.

Wally
s/v Gypsy Wind
about to head south on the ICW
for Paradise yet again...

 

[Ed Schenck]

Is the shape so odd that you can't just put a tank in there? Ronco makes such good tanks and in so many shapes. They will put the connectors anywhere you need them on the tank. You can't make one nearly as good and probably not for much less dollars. http://www.ronco-plastics.com/

 

[Peggie Hall HeadMistress]

I second the Ronco Plastics recommendation

They make TOP quality water and waste tanks for a VERY reasonable price (even more reasonable if you order through the online store at this site) and have more than 400 shapes/sizes, over 100 of which are non-rectangular...and they install fittings in the sizes and locations specified by the customer when they make the tank. Just be sure to specify WATER tank when you order.

Ed, you need to update your link to the Ronco Plastics site...this one goes directly to their marine tanks catalog: Ronco Plastics

 

[CanuckSailor]

The reason for building a tank in place is so as to not lose the capacity of the available space. Using a built in tank would probably cost me 30% of my tankage. I sail in the Bahamas, Cuba and other areas where it is not always easy or convenient to secure water, so maximizing capacity in a 34 foot boat is important, price is a secondary issue (who am I kidding here?). Showers are nice....

I had been hoping to find a PVC type material that can be 'welded' using a PVC type 'glue' that I've used successfully in my house in the past. Any thoughts on that? At the same time, I've been looking at plastic 'welding' and see some potential not just for this job but others.

 

[JohnS]

Got any pictures?

 

[Gunni]

I believe you are referring to tank construction using fiberglass flat-stock; cut, fit, and epoxied together. You coat the interior with food-grade epoxy. Nigel Calder details it in abook you already own - Boatowner's Mechanical and Electrical Manual. right?

Consider mounting them lower than your lazarette, somewhere closer to your centerline, or off-set port and starboard. Otherwise you may install a list as well as a watertank.

 

[Peggie Hall HeadMistress]

Most custom welded water and waste tank mfrs use...

...Polypropylene. However, before just writing off a rotomolded tank as too small without even looking to see what's available, consider this:

Your custom welded tanks would need walls at least 1/4" thick...Ronco tanks are approx 3/8". I don't THINK a maximum of 1/8" difference in wall thickness will cost you anywhere near 30% of capacity...more like 10%, if that much. No matter what the tank ends up to be, you'll still have to leave some room for the fittings--fill and vent at or on the top, discharge at the bottom.

If cost is not a major issue...water makers have become a lot more affordable and easier to maintain...you might want to look into adding one instead of trying to do the equivalent of stuffing a size 10 foot (water tank) into size 9 shoe (workable space for the tank).

 

[CanuckSailor]

Gunni, how did you know I own Calder's guide? Actually, I'm talking about plastic welding, using food grade plastic that I can bend to the boat's hull...I've seen a photo of it, I'm looking into it as a possibility for this situation.
The watermaker is an interesting thought, but for the money involved, I can buy a lot of water at 50¢ a gallon in the Bahamas, and that's the highest price I've found. As for thickness vs capacity, I'm thinking of the gaps between hull and tank caused by the preformed tank's shape - unless I can find the exact size I need, (and I'm still looking at the Ronco catalogue btw) - those gaps are several days worth of showers, more than a couple of spaghetti dinners and generally, just wasted space.
Every cubic inch is precious to me....

 

[packman]

plastic welding

Once apon a time I worked at an RV dealership and we used a heat gun and something that looked like a glue stick to repair plastic water tanks. I don't recall what the sticks were(I was between wives and killing too many brain cells at the time) but any RV dealer with a service dept can sell you the sticks and tank material I would think. Just my opinion but I'm with Peggy, the manufacturer can take your measurements and build you whatever you want at fairly reasonable prices, and who knows? you might decide at a later date you need the storage.

 

[CanuckSailor]

"you might decide at a later date you need the storage" - and do without water? Nope, not happening. Two tanks would cost me in excess of $500 from what I see on the Ronco page, and that's not a custom tank. I suspect that doing it in plastic would be far far cheaper and, as I noted, I'll not lose any space.
I've considered the options and fully utilizing this space is how I want to go. Even the bladder loses a lot of space when you look closely at it. I just measured and, going from a bladder to a rigid space brings me from 45 gallons to 65 gallons...times two, since I'll do this on both sides. Alternatively, I can make two 45 gallon tanks in the available space, and free up over 4 cubic feet of storage.
For those of you who don't use your boat the way I do, this isn't an issue to worry about. For me, it is.

 

[Peggie Hall HeadMistress]

Only polyethylene has be heat welded...and heat welding is the only way TO weld it. And heat welding is a bit trickier than you might think. It's not just melting some poly ("glue sticks") and sticking two tank walls together with it. That won't hold long enough to fill the tank. It takes a special tool that simultaneously heats the new poly and the edges of the two pieces so that all the melted poly runs together to become a single mass. Fittings require another tool--a spin welder that melts new poly and the edges of the round hole to create a single molten mass of poly. All of which is tricky and requires some skill...the trickiest part is ending up with a weld that doesn't have ANY air holes (leaks) in it.

Polypropylene sheets, otoh, can be "glued" together...also easier to cut cleanly, which matters when it comes to ending up with a tank that doesn't leak. But that too requires some skill. About the only thing that doesn't is cutting some plywood into the pieces you need to fit the space, gluing 'em together, then coating 'em with enough fiberglass and/or epoxy to make sure it doesn't leak.

 

[Ron20324]

It has been a couple of years or decades, but one of the boating magazines had a DIY on what you want. Memory is skimpy on the details, but they glassed in the sides and bottom of the tank. A good rubber gasket around the top, and a stury lid topped it off. I can't recall, but I imaging the lid was glassed also. Obviously, you'd have to make sure any surface the glass is on would not be able to flex.

 

[CanuckSailor]

Peggie, when you say 'glued', talking about polyprop, what sort of glue are you talking about? I had thought of glassing the space in, and may yet, but that would then involve sanding the interior smooth after glassing, then painting with a two part paint to get a surface that would not cause a 'taste' in the water from the glass. Do-able, but I'm interested in exploring this other option. The product that has been mentioned to me is food grade plastics, i.e. plastics safe to use with food products.
One other thing no one has mentioned, the installation of baffles plus an inspection plate in the lid to clean the tank from time to time. All part of the project.

 

[SamLust]

For what it's worth, I had a custom plastic tank welded up to use as a holding tank. The company was in Rhode Island and did a very nice job. Almost 20 gal and only cost about $450.00. It was worth it to me because it enabled me to obtain the the greatest utilization of otherwise useless space. I have posted the info on the company here before but if you need it I can root around and see if I can find it for you.

 

[CanuckSailor]

Samlust, I have two tanks at about 55 and 65 gallons, both with curved sides to conform to the hull. I figure, based on your pricing, that's going to be well over a grand. Isn't happening in other words.
Thanks for your offer tho - if worst comes to worst, I can buy a lot of epoxy and and glass for that kind of money and build the tanks that way.

Wally

 

[SamLust]

I kind of figured you might see it that way. You never did state your objection to the current bladders. For fresh water it would seem to me a reasonable option. Lay down bladders do NOT work for holding but water does not need a supply of fresh air like sludge does. I would think in terms of oversized bags so that as they fill they expand into and fill the compartment completely acting as a liner rather than a balloon Does that make sense?.

 

[CanuckSailor]

It makes sense, yes, but you need diameter and what a larger bag gives you is length - so you still lose a good portion of the available space. I hadn't realized how much until I did the calculation. I may actually grab some of that space for dry space, since 100 gallons is a bit much for my needs.

Wally