I believe that after this last weekend you could call the tub definitely workable and for camping almost practical. Six hours of sitting next to the campfire throwing on wood got it up to an almost scalding temperature. When you compare it to the last time it was used there was no doubt that it is getting up to temperature quicker and staying hotter for longer so the insulation really is a must for efficient operation.
The only issue now is that we used a good cubic M of wood over the a weekend…
I don’t think there is anything that we can do to the actual tub to solve this problem and that the solution has to be found in the design of the boiler. Several options have come to mind when thinking this over.
1) The pipe. Would increasing the diameter from 25mm to 50mm allow a significantly greater amount of water through? The issue here is that we’d need to coil the thing and that can be a dog, plus we’d need to find 50mm fittings for the tub.
2) The boiler shell.
a) The last two times we have used the tub we have placed the boiler in the fireplace and lit a fire around the outside as well as inside the boiler.
b) This last time we actually got the fire around the outside hot enough that the bottom of the gas bottle became red-hot and started deforming.
c) When we have used the boiler by itself we ended up with a layer of charcoal in the bottom which (along with the deformed base) seems to indicate that whilst the fire is hot enough there is not enough oxygen.
I wonder whether it would be worth cutting some bigger vents in the bottom of the boiler and just setting a fire inside it in the hope that the increased efficiency would provide the same heat output and transfer to the coil but with a decreased fuel consumption.
The other idea that has been tossed around is whether it would be better to stick with the large fire concept and just remove the coil from the boiler and place it directly into the embers?
Any thoughts, comments or ideas would be greatly appreciated.
Photos courtesy of Ash and Matt