Condensation and Insulation: the Drinking Water Tank

Once the floor was up and the cladding was off the bow wall, I could see the insulated stainless steel water tank in the alcove at the bow end. The ceiling and walls of the alcove were covered in spray foam insulation, but the floor had been left as bare metal, which was attracting condensation. The water tank was propped up along its front edge with untreated softwood stud work timber, which was rotting on the damp base.

I wanted to get on with fitting the floor, and really didn’t want another job to add to the list, but if left, the softwood would eventually rot and the tank would drop, breaking the plastic filler and breather pipes and potentially causing problems with the tank structure. To fix it at a later date would mean dismantling the bedroom to get the tank out.

So, after a few tears of frustration, it was “Out with the tank!”

With the tank out, I could now clean up the base using a wire brush and give it a spray with Lanoguard to protect against further rust. I then lined the base with two layers of 25mm insulation board (reclaimed from the floor) which would support the tank evenly without crushing. I also treated the metal in the gaps in the insulation (where the guy at Aquarius had sprayed foam into the alcove from the outside, missing spots on the back edge behind the metal supports) with Hammerite Krust, then filled them with Soudal Gap Filler spray foam. The alcove was now so snuggly that I wanted it as my bunk!

Originally the filler (black) and breather (white, covered in black sealant) looked like this. The breather was an open pipe with no fly screen, with two bits of different sized pipe held together with sealant, and the filler was a rigid plastic PVC waste pipe. There was also a lot of exposed metal around the skin fittings which needed protecting from rust.

I bought a length of Vetus drinking water filler hose (this had the smallest bend radius I could find) and a proper WRAS approved breather pipe with integrated fly screen.

It was a tight area to work in, and because the water tank was now supported across its base instead of just being propped up at the front, the skin fitting holes didn’t line up with the tank fittings at all any more!

The filler pipe took two attempts to fit; the first attempt failed as the filler pipe ended up too low and would have held water in the pipe rather than draining completely into the tank. So I took some length off the skin fitting and the 90 degree elbow piece using a pipe cutter so it would now all fit above the tank, then it was just a case of bending the hose round to fit onto the metal inlet on the tank. Flexible pipes are notoriously difficult to fit, but a flask of hot tea works a treat (thanks for the tip, John Reeve!) and after a considerable amount of swearing and a few jubilee clips (remember to put these on before you attach the pipe to the fitting!), it was done.

The breather pipe was also really tricky as it was now needed two elbows with a really short piece of pipe in between. There was no space for any extra pipe – the fittings were back-to-back, but luckily fitted perfectly! This pipe and the fittings were reclaimed from the strip-out; I just had to add an olive for the metal fitting, unlike the previous fitter who had just used more sealant! I finished it off with a bit of spray foam to cover and insulate the exposed metal.

Products Used

  • Lanoguard – green alternative to bituminous coating, made from lanolin, aka sheep’s grease
  • Soudal Gap Filler – resistant to water and heat, suitable for exterior use
  • Hammerite Krust – stops the rust and creates a paint-able surface
  • Vetus Drinking Water Hose – 32mm with a bend radius of 75mm
  • McAlpine R31 Tank Breather – WRAS approved, with fly screen

2 thoughts on “Condensation and Insulation: the Drinking Water Tank”

  1. I have read your blog with interest, as I have sent a few new buyers to Thames Solar Company. I had no idea as to the state of their build, or fit out work, certainly a company no longer deserving of my recommendation. Too high a price tag for such appalling workmanship.

    I would be keenly interested in reading the second half of your blog when you have time to conclude it.

    • From a distance, Thames Solar Electric boats look amazing; it’s only when you look beyond the shiny surface you see the reality. The fact is, this technology is brilliant – solar panels, rainwater harvesting, heat recovery ventillation, electric propulsion – it’s certainly not rocket science… but you do need to read manufacturers’ installation manuals, use the correct rated components and build within the boat regulations. I don’t want to put anyone off fossil-fuel-free living because it truly is the future (and we’re lagging way behind Europe here in the UK!) so don’t be put off; just don’t let Ryan Collingwood build it for you!

      Yes – we need to get part 2 written… last week we finished peeling all the solar panels off (they were stuck on with sikaflex and sprayfoam!) and remounting them on proper tilt-able mounts, so the blog is a little bit behind… follow us on Instagram for more up-to-date posts, and do absolutely keep your enthusiasm for the technology!

      Thanks for commenting!


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