Hello Everyone ,
I`m getting into hot water.
I have decided to use a 240 V hot water heater when connected to shore power to save lugging so many gas bottles aboard.This unit is very small and compact at 25 lts ( 6.6 US Gallons ).It will fit neatly under the kitchen bench and not take up much space.
25 lts is not really sufficient for showering for two people , so this little heater`s function is to boost the temperature of some pre heated solar hot water stored up on the shantyboat`s roof.
The pre heater will contain 100 lts ( 26.5 US Gallons ) of hot water that will be plumbed into the cold water inlet of the little water heater.
This is all experimental at this stage , but so far it looks promising.
In principal it`s all very simple , here is illustration of a similar pre heater .

These are batch heaters , meaning that the storage and solar collector are combined as one simple unit.
The main advantage is simplicity and some protection from frost ( batch heater volume ).
I anticipate having to provide an insulated cover to protect the pvc pipes from very cold nights frost ( rare here ) , but more importantly , since solar is
a " uncontrolled " energy source , to prevent the collector pipes from over heating on very hot days.

Small electric boost water heater .25 ltrs , ( 6.6 Us Gallons )

This is a photo of building the solar collector tray. 2 inch foam insulation sandwiched between 1/4 in plywood , reflective foil lining reflects sun`s radiation back towards the back of the black collector tubes..

The collector on the left will drop into the box as a complete unit once the box is installed on the roof.
http://i.imgur.com/A9G5aya.jpg
3/4 inch plywood pieces retain the collector tubes.
Paint is mat black high temp epoxy.




For initial testing , I just filled one black pipe at 8 :30 am ( ambient temp 25 C or 77 F)
4 hours later the water in that four inch pipe was too hot to put your hand into.and would have required tempering down with cold water.
I will require some insulated covers to prevent overheating on really hot days , such as we have just experienced here earlier this week.
That will require some input from me on really hot days to close the covers after heating up the collector , but it`s not a big chore is it really ?
I will need to install some digital temp probes at the collector so that I have some idea of just how hot things are getting in there , but it will just become part of a daily routine of life aboard in summer .