Replacing fresh water tank... Flexible or Rigid?

maej

maej

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My Sadler 34 has a moulded in water tank under the starboard saloon berth. 28 years of storing fresh water and the tank is riddled with osmosis like giant bubblewrap. The surveyor recomended fitting a flexible or rigid tank inside the existing one. The shape is not suitable for any off-the-shelf tanks I have seen.

I've had quotes from Tek Tanks for a custom rigid tank and from Duratank for a custom flexible one. The rigid tank is double the price of the flexible one.

What are the pro's and con's of each?
Are the benefits of a rigid tank worth twice the price of a flexible one?
 
Dowside of a flexible tank is wear, although that is less with the type you are proposing than with some. The tank inevitably flexes as water moves about and the tank adjusts to the shape of the locker. You can minimise the potential damage by making sure everything is smooth, and even lining the locker with something like neoprene. Advantages are that you don't need a breather and you may get greater capacity as the flex can fill the whole space.

Plastic tanks should last forever, they are easier to keep clean and you can fit a contents guage more easily. The high initial cost comes from the need to make irregular shapes to maximise capacity.

I have just been through this exercise when my SS bow tank leaked. A new Tek Tank was nearly £700, SS about £600 - Plastimo flexible £95. Fortunately the existing tank was repairable - but I have re-installed it in a way that it is easily removed when it next fails.

Hope this helps
 
I suppose it is out of the question to clean it all up and then line with epoxy and glass cloth?

I expect someone will tell you why this is not feasible but it would certainly be much cheaper and you would lose less capacity.
 
davidej said:
I suppose it is out of the question to clean it all up and then line with epoxy and glass cloth?
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Thanks for the reply. To be honest I haven't looked in to that route. The hull also has osmosis costing me a small fortune to put right, so I'm reluctant to put water in contact with grp where it doesn't need to be. This is probably an irrational concern and I'm open to suggestions if there is a way to reinstate the moulded in tank reliably, cheaply, safely and fairly quickly. Otherwise it's got to be a new tank inside the space.
 
Tranona said:
Tek Tank was nearly £700
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Their quote to me was nearly £1000 inc VAT and all the fittings, but it is an irregular shape...

Tank with lid removed.
watertank.jpg
 
maej said:
Thanks for the reply. To be honest I haven't looked in to that route. The hull also has osmosis costing me a small fortune to put right, so I'm reluctant to put water in contact with grp where it doesn't need to be. This is probably an irrational concern and I'm open to suggestions if there is a way to reinstate the moulded in tank reliably, cheaply, safely and fairly quickly. Otherwise it's got to be a new tank inside the space.
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But epoxy is almost totally impervious to water - unlike polyester.

That's why so many epoxy the outside of their hulls - and they only put in a layer microns thick while what I suggest would be 2-3mm.
 
When I bought my Sadler 34 it had a plastic tek tank. The yacht listed even when full due to its capacity being reduced. The tank, although designed to fit, rested on top of the ribs and this coupled with the substantial thickness of the plastic tank's walls significantly reduced capicty.

To increase water capacity I replaced the tek tank it with a flexible Duratank three years ago. So far no problems and it resolved both the tank capacity and listing problems.

The Duratank is robust and assuming no sharp endges in the yacht's orignal tank or its fittings I would anticipate it lasting for years.
 
mistyben said:
I replaced the tek tank it with a flexible Duratank three years ago.
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I'd be really interested to hear about any other differences between the 2 tanks. Does the flexi tank taint the water more than the rigid tank? Does the water sloshing in the flexi tank make more noise (when alongside trying to sleep). Does the surging of the water in the unbaffled flexi tank cause any problems or odd motions?

Sorry for the barrage of questions, I'd really like to hear about the differences from your experience. In terms of trim, my water tank was nearly empty when I bought her in November and there was a detectable list to port, but I found keeping kit bags to starboard and sitting on the starboard side of the cockpit was enough to balance her (I am heavily built though).
 
I've had a quick look around with the idea of epoxy coating the existing tank as davidej has suggested, but so far all I've come across are people saying none of the epoxies are safe for drinking water.

post 5 of this thread...
http://www.ybw.com/forums/showthread.php?t=54623

post 4 of this thread...
http://www.ybw.com/forums/showthread.php?t=185260

Are there any sutable waterproof materieals that are safe for drinking water and can be painted to the inside of a grp tank water tank?
 
Is there something we could 'paint' it with to make it safe? ie epoxy it to block out the nasties from the hull and then paint it with something every five years.
 
maej said:
I'd be really interested to hear about any other differences between the 2 tanks. Does the flexi tank taint the water more than the rigid tank? Does the water sloshing in the flexi tank make more noise (when alongside trying to sleep). Does the surging of the water in the unbaffled flexi tank cause any problems or odd motions?

Sorry for the barrage of questions, I'd really like to hear about the differences from your experience. In terms of trim, my water tank was nearly empty when I bought her in November and there was a detectable list to port, but I found keeping kit bags to starboard and sitting on the starboard side of the cockpit was enough to balance her (I am heavily built though).
Click to expand...

You should not get any sloshing sounds with the flexible tank - it expands and contracts with the contents. You can get sloshing with rigid tanks - but the Tek tank will have baffles to minimise that. Neither material will taint the water - any tainting comes from microorganisms in the water and can be controlled by weak solutions of Milton and periodic flushing.
 
I cleaned out my fixed grp tank last year using Aquaclean?? or something like that from the chandlery. On mine the whole top could be removed so was relatively easy. The lid had osmosis but decided to do nothing as none of the blisters had burst. I use a renewable water filter renewed yearly and so far the water has been fine.
 
So the only advantages to rigid tanks is they last longer and can have level gauges.
In my case the advantage to a flexible tank is a bit more capacity.

Duratank tell me the tank would still need to be connected to the breather as it's custom shape would not allow it to collapse properly as the water is used. This makes gauging how much is left a bit tricky, but not double the price tricky.

Any idea how long I could expect a Duratank to last? are we talking 5, 10, 20 years?
 
There is a water based epoxy resin which is safe for drinking water and does not taint the water at all. As you have a tank shape ready made I would have thought it worth considering coating the polyester resin with a suitable epoxy and job done. I cannot recall the make of the epoxy which a Prout Cat owner in my club had used to refurbish his underfloor water tanks. He said it was a bit expensive (for a few litres of epoxy) but was brilliant when done and he was pleased with it. I think it was a german product but a determined net search should find it.
 
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There is no more sloshing with the Dura tank than the Tek tank i.e. very little. At night sleeping it hasn't been an issues. On a rough night there is more noise outside the boat than within.

As for water taint some crew claimed at the start of the first season the water tasted of rubber. After the first few tank fulls nobody commented further.

I have bashed the boat about the Irish Sea for the last 3 seasons and there has been no problems with the tank moving about. The weight of the water in the tank fills the spaces between the ribs and holds it in place fine.

The key issue for me was the increased capacity, the rubber tank offered this and has brought the boat back into level trim.

When filled it takes up all the space with the original glass fibre tank. The only issue is to make sure the lid is well screwed down. When the rubber tank beneath is full it presses up against the lid with surprising force. As for checking how much is left I just lift the cushion and look at how deflated the tank is where filler pipe enters.
 
International have a tank sealing paint which I used several years ago it worked fine except that it took months for the smell to fade.
 
Got the same challenge

I'm about to do the same thing with my Hustler 30. The moulded in tanks are too old. The shape of the tanks is very irregular and the hassle involved in pulling apart the boat to insert new plastic tanks just isn't worth it. I'm removing the baffles from within the tank with my Dremel. Sanding down the baffle edge then lining with some neoprene. Then I'll place the flexible tanks in. I'm going for 2 x 50l tanks. If I need more water I'll take separate portable tanks anyway in case of tank problems.

I'm going for the cheap Plastimo tanks as I've used them before and had no problems with them in the past. If by some quirk they only last a few years that's fine by me as they are so cheap.
 
If you want to paint the tank then pretty much any pure epoxy will be OK. The one Viago suggested is no better - or worse - than many others. The reason nobody will tell you it is OK is because it needs to have a potable water certificate and that is expensive to get. Too expensive to justify selling into the yacht market anyway. Most of the major marine paint companies have certified products but they are only available in large pack sizes for ships and rigs. Before epoxies they also used to sell conventional, certified, products but they are no longer needed, and the certification cost has become prohibitive. I'm pretty sure International used to sell a single pack product for yachts with certification but long gone now. If you can get application conditions good enough (warm) then Gelshield, the solvent free one, should be fine as will Blakes SFE. Being solvent free they will become taint free more quickly than solvent based epoxies. I would be wary of water based epoxies due to the time you will need to leave them to cure before being suitable for long term immersion in water.
If you want a certified product might be worth giving Teamac a ring. They supply a lot to fishing boats so might have a certified product in 5L or or even smaller.
 
I'd go for the Duratank. Quality miles ahead of a Plastimo. I once owned a Sigma 33 with built in GRP tanks, when I eventually decided to give them a proper clean by unscrewing the lids, I found them lined with a flexible polyester tank, as they had reverse osmosis, the whole tank covered in blisters.
 
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