On Wotan we only ever had hand-pumped cold water. Moving onto Tilly was like a dream with pressurised water from the tap, and a hot water tank. However, as with everything my dream of a hot shower wasn't to be until the old hot water tank was ripped out replaced.
The existing water tank on board was an not insulated, only had an electric immersion coil fitted and had no pressure safety features...
In March 2014 after that really cold winter and ice/snow in February and March as well as a new baby (baby number 2) due to arrive in just a few months we decided to 'get round to it'.
We measured up the existing space and realised we could get a bigger tank in than the existing tank which was only about 45 litres. Once we figured out the terminology for what we were looking for, we went about finding quotes. Again, we had some ridiculous quotes but a fair amount more were reasonable as these tanks are standard household equipment. We went with a custom made 'triple coil indirect vented water tank' with dimensions of 1200 x 350 (95 litres), it cost us £500 and we bought it through PTS in Bitterne, the tank was built by RM Cylinders - we did try to go direct but they only work through distributors and so pointed us in the direction of a local one.
Note: You can get specially made boat tanks, but they are pricey, small and I do wonder if they are really necessary.
I know, what does all that mean a 'triple coil indirect vented water tank'?
Basically the 'triple coil indirect' part refers to the fact that we have 3 coils within the copper tank which are plumbed onto external pipes from other heating circuits. Inside it must look a bit like this:
We have 3 coils because we wanted a coil for our mikuni diesel heater (a wet system which runs radiators too), a coil to be run off our boat engine and a coil to be run off a solar water heater (which we plan to build and fit on deck).
The cylinder took 2 days to make and arrived within 3 days of my order and deposit. We ordered it in time to coincide with a visit from my parents, my Dad helped us fit it and all the pipework for our mikuni diesel heater.
In addition to the indirect heating coils we fitted a thermostatic immersion coil, 2.7kW (the marina supplies us 16A at 240v which is about 3.7kW, that means we can't have much else running at the same time if we want to use it, but its a good back-up source and heats the tank in 30mins or so). The thermostat is a bit of a safety feature, it switches itself off at a certain temperature so if we did ever forget to turn it off the water wouldn't continue to get hotter and hotter and build pressure. Of course it also just means we can decide what temperature we want to heat the water to (if we were to leave it on it would enable us to save energy).
Talking of pressure, apparently exploding water tanks are not uncommon on older boats!
Now you might have noticed that we have a 'vented' old style tank, our water pump provides a 2.5bar pressurised water system and our tank is rated as a normal home-use tank for 1bar (tested to 1.5bar). So putting 2.5bars into the tank doesn't seem like the best idea. I'll be honest with you, we didn't notice that to start with, mostly because we never really thought too much about what the tank was rated for. Our tank didn't explode in the 6 months or so that we used it in earnest before the realisation... However, once we realised it played on the mind, so we needed to re-think our set-up.
We did have a pressure release valve fitted on the hot water outlet pipe with a T-fitting running a pipe outside the boat, but it was 3bar and when we discovered the tank was only rated for 1bar it was time for a change.
Where there's a boat job to be done, it always takes more than one go to get it right.
So here was the second iteration of the system. We picked up a 40 litre feed-in tank from our local DIY store which has a float valve fitted. This is the smallest tank we could find and it fits nicely in an existing space about 1 metre above the hot water tank. The cold water is pumped into the feed-in tank automatically, stopping when the float valve blocks off the pipe and allows the cold water to be re-pressurised and that water is gravity fed into the hot water tank. To get pressurised hot water we fitted another water pump on outlet from the hot water tank, with a temperature control valve just before the pump, set at around 45 degrees (the pump is rated for up to 60 degrees).
If you don't know much about boat water system pumps, the pumps (cold and hot side) are pressurising pumps. They detect the pressure in the system after the pump and therefore pump until the pressure in the system is above the threshold. When you open the tap (or the float valve) and release the pressure the pumps runs and when you close them it stops.
Now the risk of exploding tanks was averted, all that remained was making sure we were keeping it warmer for longer.
The tank came with 50mm of insulation to keep water capacity in the small space. We added some loft insulation around the tank to keep it warmer for longer and it seems to work well.
Hot water at last, well until the next repair job!
It's really nice not to have to go up to the marina showers in the depths of winter (its a good few minutes walk up there). Also, invaluable for hosing down emergency baby/toddler situations.