Building a fibreglass water tank

[Bajansailor]

I am slowly building a new 'built in' water tank in the keel of our Challenger 35 using fibreglass panels as in the photo below - this tank will replace a stainless steel tank that lived in this space previously.

I made up flat panels for the four sides - the aft panel is resting against the bulkhead at the end of the photo.
I still have to finish sanding away the remains of the white paint on the hull before I glass these panels in.
I will put in a couple of transverse baffles, and a Tek-Tanks inspection port at the aft end of the cover panel.
These cover panels will be bedded down onto fibreglass angles - one of these angles is shown duct taped temporarily on the port side of the tank.

I was thinking about lining the interior of the tank with a layer of glass cloth with epoxy resin, on the principle that it should be more resistant to osmosis et al than simply painting the interior of the tank with gelcoat - what are your thoughts on this?

It would be nice to have the interior of the tank all painted bright white, so if it is OK to use epoxy as a finishing coat, I could perhaps gelcoat it first before applying the epoxy, if the epoxy does not have an effect on the taste or quality of the water within (I have heard conflicting reports about this).

Changing tack, I am also trying to remove a substantial bronze skin fitting which housed the now defunct Stowe log transducer, and I am having a hard job getting the nut on the fitting to shift - there is not much leverage room for a pipe wrench, as can be seen in the photo below.

And this is the only way that the wrench will fit on the nut. I have tried adding extensions to the handle, walloping it with a hammer, but no go so far.
Any ideas?

 

[boatbuilder]

Hit the nut with a sharp cold chisel, as this only bronze it will be soft. Cut it on opposite sides and it will fall off.
If the fitting itself won't come off cut through lengthwise with a hacksay blade ad then collapse it with a hammer.

 

[Burnham_Bob]

no idea on the tank but a friend of mne was a marine engineer and he's shifted stuck nuts on my boat by banging them both sides at the same time with hammers.

You have to hit opposite sides at the same time but it really does free them. Or at least it has on my boat.

 

[matelot]

Once upon a time I investigated coaTING THE INSIDE OF THE WATER TANKS ON MY BOAT WITH EPOXY. i WAS WARNED OFF BY THE MANUFACTURERS - NONE OF THEM HAD APPROVAL FOR POTABLE WATER. whether this was an issue of the cost of approvals or something nasty leaching out of the epoxy I do not know.

given how cheap stainless tanks are - why change?

apologies for the caps but couldnt be bothered to re-type.

 

[catalac08]

I am not an expert but I would be very concerned about the taste of the water from a fibreglass water tank, particularly a newly moulded one.
I replaced stainless tanks with Plastimo flexible tanks last year. The advice from Plastimo for these new tanks was to initially flush the tanks with vinegar to remove any plasticky taste from the water - I did that but then had water that still tasted of vinegar after 5 tank flushes. I then used a tank cleaner (chlorine based type) which removed the vinegar taste but has left a chlorine taste. I finally fitted a filter which leaves the water tasting fine but the pressure drop across the filter means the small electric pump can only produce a very slow flow.
Sorry for the rambling (but always better to avoid others mistakes). Have you considered rather than painting the tank interior with ordinary paint using one of the purpose made tank interior paints, I think these are chlorinated rubber based.
Whatever you do I think you need to consider the taste issue very seriously - I am sure there arte many on the forum who can advise exactly the best thing to do!

 

[earlybird]

You'll be lucky to avoid destruction of the skinfitting. An angle grinder with a slitting disc would be useful, And a hacksaw blade in a pad handle. Add:- Hempel do an epoxy coating for potable water tanks.

 

[Bajansailor]

Thanks for all the advice above!

I shall try using a sharp cold chisel on the skin fitting nut, as suggested by Boatbuilder.

Re the old stainless steel water tank, the welds on the seams have gone porous (again! I had them all re-welded about 5 years ago), and the water within is a muddy chocolate colour, hence the reason why I decided to build a fibreglass water tank - and I should get about 10 gallons extra capacity this way as well.

Re coating the interior of a water tank with epoxy (rather than eg gelcoat) - what are the water tanks on these ultra modern Vendee boats made from? I am thinking they might be epoxy, or do they just have flexible bladder tanks?

 

[Kylora]

Regarding the skin fitting. I would agree with EarlyBird. Following advice that 'time is money' I had to do the following when I couldn't get the old gate type seacock loose from the skin fitting. I used an angle grinder with a cutting disc as opposed to a grinding disc. Carefully cut two slots across the external flange in the shape of a X, cut as deep as you dare. You will find that you can lever each of the quarter segments away from the hull without causing damage. Tidy things up as necessary and knock the remainder of the fitting into the hull.

Ash

 

[Gandolfo]

I'd install a double-skin plastic bag type tank in that nice smooth void. Easy to install, easy to connect up, easy to remove through a small hatch in the floor, and easy to clean. I had one under the floor of my Warrior 35 and it did years of trouble-free, taste-free service. Bag collapses as water is used, so less air - water contact, which helps prevent contamination etc.

 

[Pasarell]

If you just gelcoat the tank I would expect to get osmosis fairly quickly - couple of years or so. It won't be disastrous but will taint the water eventually.
Most pure epoxies on the DIY market should be OK to use but they won't have potable water certificates due to cost of getting it for a very small market. Same products sold under other names for large scale use may well have the certificate so it might be worth having an "off the record" chat with technical people from International / Blakes etc.
Personally I would put a flexible tank into the nice neat case you have made. Easy to clean and remove and relatively cheap to replace when the water starts to taste.

 

[leomagill]

I'm in the process of doing very similar myself at the moment, east coast fibreglass supplies do a food grade resinpolyester but you have to use a different catalyst to the usual mekp and have to 'post cure' at about 80 degrees c for several hours after layup to drive out the styrene to stop it affecting the water (I think it's called crystic 491 or something).
I've opted for a glassed in comparment and a single skin liner from dureflex, they seem very helpful, they also do a water conditioning kit that uses porous beads to keep the water sweet without aquatabs.

 

[Bajansailor]

Thanks for all the replies above, especially the suggestions re installing a flexible water tank - sometimes I can't 'see the wood for the trees', and of course that is logically the way to go!

I was too focussed on installing a 'built in' fibreglass tank, but then there are all sorts of possible complications re cleaning it out, if it leaks later on, etc - flexi has got to be a better way to go.

I do actually have a 100 litre rectangular Plastimo tank which I was going to install up forward, but it is too big..... I have just filled it up in the shower here, and I think it should fit even with the side panels as shown in the photo above - I will take it in to the boat tomorrow and test it there.
And if it is too wide for the side panels (shown duct taped in temporarily), then I will keep them for something else and allow the bag to spread sideways a bit each side under the floor, and find another way of restraining the bag.
And perhaps let it rest on a rubber or neoprene mat to try and reduce chafe.
There should even be room for two 100 litre tanks in the space available, one in front of each other. I'll probably be over in high latitudes for a week or so later this month, so will have to come armed with a shopping list.... /forums/images/graemlins/smile.gif

 

[Graham66]

Wouldn't reccommend polyester water tank for potable water especially when built in this manner, laminate needs to be post cured at the manufacturers reccommended temperature for something like a month prior to coating with epoxy. there will be no way to totally seal the tank with a potable paint coating once the lid is on and then styrenes and the like can leach into the water leaving a foul taste. I would purchase a flexible tank that will fit the space if you want "tap" fresh water to use /drink.

 

[Heckler]

Same as another poster, oin the late to mid 90s, bneteau used moulded fi glass water tanks, they ALL get osmosis in them, no structural damage but the water tastes and smells foul, and when selling time comes the surveyor sucks his teeth and you get another grand knocked off your price.
Stu

 

[rhumlady]

Try to put something under the flexi tank to allow air to circulate as this will stop condensation which I have seen leading to small blisters arhgggg....

 

[Andrew41]

Big nuts

Use an angle grinder to remove the flange nut? It may not get in close enough and I wouldn't risk an angle grinder that near the bottom of my hull!
Get a Dremel. I finally bought one a month ago and have used it so often on the boat it's become my number one tool. It's got big muscles but can get into tenny wee spaces. I've broken a few of the bits but they're cheap. I wouldn't leave home without it now. A Dremel 300 is 125watts so it even works off my inverter. (Disclaimer - other wee rotary tools are available).
Also, have a look at the water tanks direct website as they have all shapes & sizes of poly tanks in case you can't get a flexi tank long & thin enough. The non-marine poly tanks are depressingly cheap and tempting. I'm busy repairing my leaking Jeanneau stainless tanks so I've been looking at options. Just now I'm going to Microseal the insides and epoxy the outsides which is how I found this thread. No more chat on that subject just now as there are lots of threads on this already!

 

[rogerthebodger]

Have a look at this being food grade epoxy resin.

http://http://www.flowcretesa.co.za/products/Ivory_340_FG/