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Large water tank: where to stash it, what to make it out of


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Currently I have an integral water tank up the pointy end in the usual way. The super cheap borescope ("inskam") shows it to be caked with rust, and that's probably why the pump seized. I don't want the horrid job of painting it every couple of years, I don't want to drink water that's been in a painted tank, and I'll surely want a larger capacity than whatever this one holds.

 

So more questions,

  • I've heard stainless steel can crack at the welds. Is there a better material? Anyone heard of bunding a water tank, other than "it drains into the bilge and the carpet drinks it up"?
  • For those with really large water tanks, where do you stow them?
  • Anyone have multiple tanks distributed around the boat? I'm leaning towards the idea of having multiple tanks with a pump each.

 

The modular approach to water tank capacity suits my plan of gradually refitting the boat.

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9 minutes ago, wakey_wake said:

So more questions,

  • I've heard stainless steel can crack at the welds. Is there a better material? Anyone heard of bunding a water tank, other than "it drains into the bilge and the carpet drinks it up"?
  • For those with really large water tanks, where do you stow them?
  • Anyone have multiple tanks distributed around the boat? I'm leaning towards the idea of having multiple tanks with a pump each.

 

The modular approach to water tank capacity suits my plan of gradually refitting the boat.

Loads of stainless tanks around. Cracking is a very rare problem. Plastic tanks, either rigid, or flexible are available. A bilge pump in the bilge that a leak would go in to is a better solution. Bunding is generally used where you want to contain a nasty liquid, not potable water. Just pump it overboard. Most leaks happen in the plumbing, not the tank anyway.

Tanks should be low down in the boat for stability. Ideally they should be balanced port to starboard, so the boat doesn't have weird lists as the tanks are filled and emptied.

Multiple tanks don't need multiple pumps. The tanks can be interconnected so one pump draws from all. Valves can be used to switch the tank being pumped, or if all valves are open it becomes effectively one big tank. They can also be filled from a single point too. Care needs to be taken with air vents so they fill and empty properly, but can be done.

Jen

 

 

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1. Plastic tanks. Plenty of suppliers out there who sell both standard sizes and bespoke shapes.

2. Under the fore deck i.e. the space where current integral tank is. Usually inserted from inside the cabin, which is fine on a new build or a major refit, but a bit impractical otherwise.

3. If you have multiple tanks you should arrange them in a connected chain so that you fill up at one end and draw water from the other end. That will keep the all the water fresher and avoid stagnant corners. Each tank will need to be vented.

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If you put the new tank in the existing tank space (which otherwise will be wasted) then you will need to cut away the bulkhead. You will also need to remove almost all of the rust and paint it otherwise it will keep rusting. Even after this you will still likely get rust as condensation will form on the new tank, and this rust will be inaccessible. If you want maximum water tank capacity then you will have a lot of wasted space between the new tank and the hull sides.  The obvious approach is to properly derust the existing integral tank and paint it in epoxy that should last many years.

 

...............Dave

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Candlebridge Fabrications at Blisworth Tunnel boats made and fitted us a nice one in stainless.  They cut the front deck out as that formed the rusty lid of the old water tank, dropped the new one in, and made a new deck floor, incl lockers.  A top job.

 

Its probably 90% the volume of the old "tank" as it doesn't have the curved sides, but is clearly the sensible approach.

 

We can recommend them.

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10 minutes ago, dmr said:

If you put the new tank in the existing tank space (which otherwise will be wasted) then you will need to cut away the bulkhead. You will also need to remove almost all of the rust and paint it otherwise it will keep rusting. Even after this you will still likely get rust as condensation will form on the new tank, and this rust will be inaccessible. If you want maximum water tank capacity then you will have a lot of wasted space between the new tank and the hull sides.  The obvious approach is to properly derust the existing integral tank and paint it in epoxy that should last many years.

 

...............Dave

Or get a man in to do it

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1 minute ago, ditchcrawler said:

Or get a man in to do it

 

A job for an unemployed yoof, the modern equivalent of sending them up chimneys?

 

As well as getting a man to do the water tank I also got a friend to do the gas locker, tomorrow I have to get the angle grinder going and repay that debt ?.

 

................Dave

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1 hour ago, system 4-50 said:

I have 2 x 400L plastic tanks under my big fixed double bed.  Tiny list change empty to full.  1 pump drawing from the top of both tanks. 1 fill point to both tanks. 1 air vent connected to both.

That is almost exactly what we have, flat rectangular tanks, window cleaners tanks in fact, strapped down with ratchet straps and wrapped in foam board stuff in case of condensation - we've never had any in fact  - our tanks have also got big screw on lids so we can see what is swimming around inside.

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With Innisfree we had a bow tank + I  had 2 rectangular polyprop tanks made and installed them lengthwise under the dinette, one midships for level trim and one alongside so that it's contents could adjusted to counteract port side holding tank as it filled up, worked well. 

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10 hours ago, wakey_wake said:

Currently I have an integral water tank up the pointy end in the usual way. The super cheap borescope ("inskam") shows it to be caked with rust, and that's probably why the pump seized. I don't want the horrid job of painting it every couple of years, I don't want to drink water that's been in a painted tank, and I'll surely want a larger capacity than whatever this one holds.

 

 

So what are you going to do with the space once it's no longer a water tank? If you install a stainless or plastic tank in that space you'll have to do something to prevent condensation otherwise it will continue to rust. On that subject, how do people with water tanks within heated cabin spaces prevent them from sweating?

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36 minutes ago, blackrose said:

 

So what are you going to do with the space once it's no longer a water tank? If you install a stainless or plastic tank in that space you'll have to do something to prevent condensation otherwise it will continue to rust. On that subject, how do people with water tanks within heated cabin spaces prevent them from sweating?

With Innisfree no condensing, the onboard water soon warmed up + polyprop tanks helped there and we rarely had to empty them so minimising cold water top up. 

 

ETA: No tank insulation, + a few days before pump out we would switch over to ballast tank and use that up, then it would be a case of refilling it gradually. 

Edited by nb Innisfree
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12 hours ago, wakey_wake said:
  • I've heard stainless steel can crack at the welds. Is there a better material? Anyone heard of bunding a water tank, other than "it drains into the bilge and the carpet drinks it up"?

Only a straw poll of one, but my SS tank has been in 15 years.

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7 hours ago, Lord Maffi of Oxford said:

Only a straw poll of one, but my SS tank has been in 15 years.

My present one is 28 years old 

Still goes bang when full ?

 

On the barge we had a 1100L stainless insulated tank under the bed in the bow and 500L plastic tank under some cupboards midships, both tanks were insulated to prevent condensation.

 

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11 hours ago, Bee said:

That is almost exactly what we have, flat rectangular tanks, window cleaners tanks in fact, strapped down with ratchet straps and wrapped in foam board stuff in case of condensation - we've never had any in fact  - our tanks have also got big screw on lids so we can see what is swimming around inside.

Them's the one.  1" celotex all sides & base & top.

How do you fill them ie know when they are full? What size is your filler pipe?

I fill mine under mains pressure and rely on a depth sensor to cut off the input.

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24 minutes ago, system 4-50 said:

Them's the one.  1" celotex all sides & base & top.

How do you fill them ie know when they are full? What size is your filler pipe?

I fill mine under mains pressure and rely on a depth sensor to cut off the input.

Ah, this is one of those jobs that I have never got around to finishing off, filler pipe is about 1.5" or something metric. Someone sits on the bed with the mattress folded back and unscrews the lid and shouts 'B****** hell turn the water off we're sinking'  I'm sure there's a better way, maybe I'll get around to it this year.

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Bladder tank made from inflatable boat material is an easy solution.  Mine was custom made by Hovercraft Consultants - don't know if they are still in business.  Can be installed inside an existing tank ideally.  It had a webbing loop at the top 4 corners so it could be suspended and held in place. 

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I didn't read all of the above - but my two-pennorth says it all depends on who supplies the tank and how good they make it.

 

Our boat was built well north of Watford or Birmingham and I aked the builder to supply a 'proper' galvanised tank (NOT a hot dipped one. That he did and made it in a shape to fit under the fore deck. It's been there for 31 yeas and hasn't leaked or corroded

 

Contrarywise I bought two heavy duty plastic tanks for the loos from a midlands maker. I asked for and received heavier guage plastic. Solid as a rock and don't bounce when you sit on the domestic sized pan.

 

To some extent what you get depends on luck - especially if you're a southerner.....

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12 hours ago, Lord Maffi of Oxford said:

Only a straw poll of one, but my SS tank has been in 15 years.

 

5 hours ago, Tony Brooks said:

Mine was 29 years when we sold the boat.

 

5 hours ago, Loddon said:

My present one is 28 years old

OK, I'm sold on stainless! What thickness are these?

 

I know some aren't fussed but I would rather not trust any plastic, especially epoxy or bitumen, for my drinking water. Having a separate drinking water tank is another option, but seems like a faff-sink.

 

On the other hand having multiple tanks in daisy chain (for freshness - good point) and then taking drinking water out of the first in the chain... that seems clever, and makes it possible to use lower quality water (rain / filtered ditchwater) for washing. Maybe it's the kind of clever that causes more problems down the line.

 

There's still the problem of where & how to get it/them in, but the basic choice is a starting point.

 

5 hours ago, Loddon said:

Still goes bang when full ?

Is that the transition from convex to concave? It suggests there's not enough support around it...  but still 28 years says that's not a real problem.

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11 minutes ago, wakey_wake said:

 

 

OK, I'm sold on stainless! What thickness are these?

 

 

Is that the transition from convex to concave? It suggests there's not enough support around it...  but still 28 years says that's not a real problem.

 

1. No idea because I can not get to any part to measure it.

 

2. Its not support as such, its water pressure or a breather that won't let the air out fast enough. I think I wedged a piece of wood on top of ours to stop it banging.

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5 minutes ago, Tony Brooks said:

Its not support as such, its water pressure or a breather that won't let the air out fast enough. I think I wedged a piece of wood on top of ours to stop it banging.

Yes but the bang tells me when to stop filling ?

 

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17 hours ago, dmr said:

If you put the new tank in the existing tank space (which otherwise will be wasted) then you will need to cut away the bulkhead. You will also need to remove almost all of the rust and paint it otherwise it will keep rusting.

Yes, the requirements for not flooding the bow bilge make it an inconvenient sort of space most suited to liquid storage.

 

I think I have to get away from the idea of "do the job once and it won't need doing again", especially where steel is concerned. Access is required all round the outside of the hull and the inside is only better if it's guaranteed to stay dry. I'm leaning towards the format of "how much of my boat do I have to destroy to a) check up on that or b) properly service it".

 

"Check up on" including that it hasn't caught fire when welding on the other side, and "service" including "clean before / repaint after welding".

 

So the water tank has to be able to come out for maintenance. Maybe if it's in two or three pieces?

 

 

17 hours ago, dmr said:

Even after this you will still likely get rust as condensation will form on the new tank, and this rust will be inaccessible. If you want maximum water tank capacity then you will have a lot of wasted space between the new tank and the hull sides.  The obvious approach is to properly derust the existing integral tank and paint it in epoxy that should last many years.

 

If the space around the tanks is sealed in (with a small breather hole), and there's a desiccant in space which can be replaced easily, then any kind of paint seems likely to last well. That doesn't solve all the problems though.

 

Has anyone ever used electrolytic copper plating as an inner hull treatment, for integral water tank or otherwise?  The wave of a tape measure says 6 kilos would give me 0.1mm thickness, which is affordable in price of copper and probably plenty thick enough. The wave of GNU Units says, unless I've botched it, that 94 mol of copper can be plated with 200 amps in 25 hours, so it looks afford in time and electricity too.

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