Not a Time Machine – Part 6

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


Not a Time Machine – Part 5

The Time Machine Hot Tub is having its second proper outing this weekend with a holiday to the Coromandel. Last time it was used in the wild we had an issue in that we weren’t able to get it quite hot enough. Kauaeranga Valley is notorious for being several hundred degrees below zero at night so it was decided that something had to be done.

The only difference between the first time it was used (when it worked really well) and the second was that we were able to use a 12v computer fan as a blower for the burner. The second time we didn’t have the luxury of a 240v outlet for the transformer for the fan to plug into and as a result weren’t able to get the fire as hot as the first time. As this will often be the case going forwards out only option was to increase the efficiency of the burner and insulate the tub to decrease heat loss.

We really wanted some sort of closed cell foam to prevent it getting waterlogged, something cheap and something flexible. Foam bed rolls provided to be an ideal solution and 3 double bed rolls were acquired from The Warehouse on sale.

These were then cut into strips

And inserted between the tub frame and outer cladding

Until it looked like this

We managed to attach the remaining bed roll to the roof of the tub by “Man Sewing” it on with wire.

Hopefully that should make enough difference to the performance or it looks like someone is going to have to spend most of saturday blowing air into a fireplace.

Not a Time Machine – Part 4

So there hasn’t been an update for a while, a lot has been happening however both on the Hot Tub and on other projects. A couple of weekends ago saw a lot of progress with the Hot Tub, including firing it up and soaking in it for the first time.

On Saturday Tim and I hired a pipe bender from the local Hire shop and proceeded to embark on a 3 hour pipe bending marathon with the help from William and Mark. The first bend went horrifically averagely with the pipe turning slightly egg shaped and dented on the outside where the rollers pressed against it. Filling the pipe with sand and capping the ends with gaffa tape and placing some patches of carpet around the rollers seemed to solve most of these problems.

The other issue that we had was that we were trying to bend 4m of pipe with a pipe bender that was designed to be mounted upright on the ground with very little ground clearance. The solution to this was to tip the whole thing on its side and spiral the pipe out and around the frame of the bender as it was bent.

Bending angles etc were all done by guesswork but the result seemed to work out pretty smooth.

Once the pipe had been coiled the required amount we then had to address an issue that because we had had to coil the pipe through the frame of the bender, we had ended up with a coil that was about 10cm too tall to fit inside the gas bottle.  After much jumping up and down on it, squeezing it in the bench vice and taking blurry pictures of it we managed to compress it enough to fit.

From here we cut slots in the sides of the LPG tank and then took it out to Reub’s farm for some late night Arc Welding.

Later that night we fired up the Tub at about 6pm for a test run to see how it would heat. Minor success but nothing soakable was achieved.

Next day (Sunday) a better planned approach was devised, wind shields protected the boiler, a chimney and blower helped with airflow and half an old mattress helped insulate the top of the tub.

In this next photo you can actually see the flames coming out of the holes at the bottom of the boiler because of the volume of air coming from the fan.

During the week Reub and I put some more work into the boiler, Reub finished welding up the sides of it and I cut down an umbrella stand and turned it into a boiler stand.

The next weekend we spent Friday night and Sat camping in the Coromandel, On Sunday however we decided that the Tub needed another outing so we dragged it out to Reub’s parents place and set it up in a couple of fireplaces in the reserve. Doing so meant that we had to join 5 garden hoses together, run them down through some bush, over a mangrove mud flat and then up through a gorse bush.

Even after getting the hose down there however we still needed to get the water down, this involved pumping it from one tank to a second and then gravity feeding it from the second to a third.

Several hours of heating produced semi acceptable results, Reub’s Shrub (TM) heated up a lot faster but the size meant that it was only approved for Dual Occupancy.

Whilst not exactly up to standard yet this project may be shelved for a while in favor for other projects. Going forward we need to look at improving the efficiency of the boiler by cutting more vent holes in it and trying to get it to burn better on just wood. We also need to look at insulating the tub better so less heat is lost to the open air. The only other change that needs to be made is the inclusion of a wooden rim around the top of the tub, mostly for aesthetic reasons.

Not a Time Machine – Part 3

Yesterday whilst all the still action was going on we also managed to do some work on the burner for the hot tub.

This is the finished product of about 45mins of hard core angle grinding. Wanting to cut straight through the middle of the tank meant that we also had to cut through two layers of the tank skin as apposed to just one as the manufacturer obviously decided that as well as welding the tank together they should flare the bottom section and slide the top into it.

First off however we had to remove the valve from the top (Enter spanner and hammer) and purge all the gas from the tank by filling it with water (IMPORTANT STEP FOLKS)

Now that this has been cut in half the next step will be to cut another hole in the top half for putting wood in and drill some holes in the bottom half for ventilation and for all the ash etc to fall out.

This morning at 7:15 I picked up the SS pipe for the coil from East Tamaki, (pic to come) Once this has been bent (anyone got a pipe bender?) the slots in the tank can be cut and the pipe installed.

Ive been thinking about how to join the top and bottom back together once its done. Welding seemed like a go at the start but now I think ill probably just make 3-4 steel drilled plates approx 1 inch x 4 inches and bolt them onto the side to hold the two halves together. Then if something goes wrong in the future or if changes are needed to the burner it’ll be easier to get them apart.

Since last time the hole for the outlet has also been cut in the corrugated iron. The hole for the return to the tub still has to be done though, mostly because its a real dog of a job and I want to put it off as long as possible. Same goes for the hole around the drain at the bottom of the tank which because of the corrugated sheeting is inaccessible.

Not a Time Machine – Part 2

Chopped the lid off the tub the other night with help from brother and father. Believe it or not it’s not that easy to cut the top off a wobbly 1000L plastic bin at night with only a hacksaw.

It worked though and after a bit of sanding and the cleaning to end all cleanings we water tested it the next day to see if any of the fittings leaked and generally what it would look like with water in it.

The large outlet down the bottom will be for draining the tub, the black one to the left for the outlet connection to the heating coil.

Yesterday Reub and I shot out to M10 Mega and brought several sheets of corrugated roofing to wrap around the side.

After cutting it in half to give us 900mm x 634mm sections we riveted all of them together to make a long ribbon.

Flipping reflective and bright when you take it outside 😛

One end of this was then riveted to the cage, the cage was then rotated, the ribbon tensioned and then tacked on the far corner. We then worked back securing the sheeting to all 4 horizontal rails 3 times on the short sides and 5 on the long.

Tub was then rotated twice more, the ribbon was tensioned, cut to length and joined to itself. Once again we went back and finished riveting it to the cage.

Brother and I then attached the top of the tub to the cage, mostly to stop it from getting pulled out when people hop in and out of the tub.

Almost finished product. Still need to put on the wood trim at the top, cut the inlet and outlet holes in the corrugated metal and cut out around the drain valve so you can get your hand in. Once the tub is fired up we’ll make a decision as to whether we need to insulate or not.