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  1. #1
    Join Date
    Dec 2004
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    4,262

    Default Building a fibreglass water tank

    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?
    Here is a useful guide to Barbados - http://doyleguides.com/barbados.html

  2. #2
    boatbuilder is offline Registered User
    Location : Millbrook, Cornwall
    Join Date
    Apr 2005
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    2,619

    Default Re: Building a fibreglass water tank

    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.

  3. #3
    Join Date
    Jul 2001
    Posts
    213

    Default Re: Building a fibreglass water tank

    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.

  4. #4
    Join Date
    Sep 2008
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    2,062

    Default Re: Building a fibreglass water tank

    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.

  5. #5
    Join Date
    Nov 2004
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    1,067

    Default Re: Building a fibreglass water tank

    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!

  6. #6
    earlybird is offline Registered User
    Location : Cumbria; U.K.
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    Aug 2004
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    2,156

    Default Re: Building a fibreglass water tank

    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.

  7. #7
    Join Date
    Dec 2004
    Posts
    4,262

    Default Re: Building a fibreglass water tank

    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?
    Here is a useful guide to Barbados - http://doyleguides.com/barbados.html

  8. #8
    ashonavega's Avatar
    ashonavega is offline Registered User
    Location : Kip Marina, Clyde, Scotland, UK
    Join Date
    Feb 2005
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    548

    Default Re: Building a fibreglass water tank

    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

  9. #9

    Default Re: Building a fibreglass water tank

    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.

  10. #10
    Join Date
    Jan 2007
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    828

    Default Re: Building a fibreglass water tank

    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.

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