Larger slim oval ultralight tent stove

The slim oval ultralight tent stove (~950 g) for winter trekking has large cooktop for 2-3 pots for snow melting, boiling and cooking. It cleanly burns ~410 g of wood/h and has an estimated heating power 890 watts.

Introduction

For some time I have been using my small ultralight tent stove for alpine backpacking adventures as a source of warmth and cooking in an ultralight tent. Building on this success, I have sought to develop a similar but larger stove that works on the same unusual inverted burner principle that makes a hand full of bush sticks burn efficiently, systematically and cleanly to produce abundant and intense heat.

Larger ultralight tent stove

Stove mounting

Off snow mounting. The stove can be mounted in many ways. Off the snow, it can be mounted on the ground that id cleared of combustible materials. It also can be set on three rocks to keep it up of the ground and to set the cooktop at the prefered angle. My prefered option if possible is to set it up on a large slab of rock that is in turn set on three or more rocks. This configuration creates a hot bench for the tent to; dry fuel sticks, keep food and drinks warm and to dry socks, gloves and hats. Eventually, the underside of the rock slab will become quite warm and suitable for drying things. The last pleasure is that a large rock slab will act as a heat bank and radiate heat for hours after the stove has been put out. “This set up takes a little effort, but is very rewarding, particularly, if you are pinned down by bad weather for some time.“

Deep snow mounting. The stove is provided with 6 clevis mounting devices that are welded on around the perimeter. At the camp, these can be connected to articulated mounts that can be fitted to stove legs made from bush poles. The stove legs can be driven into the snow to mount the stove at a comfortable height above the snow surface. An alternative fitting that connects to a tent pole can also be used as one of the three minimum support legs. With bush pole legs and a little clever twitching of nylon cord or cable ties, a wood drying/storing rack can be formed below the stove.

Stove mounting without a tent pole. My tents are designed to be able to be erected without a tent pole (see below). This means that there is great flexibility in the mounting of a stove, particularly on snow.

Field testing- time for procrastination was over

This prototype stove had many bench tests but had never had a real field test in the snow and I have found that such field tests in the snow, are the harshest ones and usually reveal design deficiencies and areas for improvement. I also find such tests are easy to put off.

“Success is nice, but failure is a better teacher, and such learning is never immediately a nice experience.” Consequently,  I was leading an annual snow camp for the Strzelecki Bushwalking Club at Mt. St Gwinear. We had exceptionally good deep snow for the event (for skiers and some snowshoers). I could procrastinate no longer about the field testing even at the risk of failure in front of a small audience of vocal ‘die-hard’ snow campers.

I took my large ultralight tent and erected it, without a pole, using a suspension cord from an overhanging snow gum branch. In the tent, we excavated steps leading down to a large snow pit so that we could walk into the tent with a central stove and sit around it the on the snow bench, on blue sealed cell foam mats, (with ski boots on). This made a comfortable heated communal shelter for the group to melt snow, make dinner, have hot drinks, share stories, and exaggerate the skiing exploits of the day.

In the middle of the pit, I mounted the stove on four long bush poles that were driven into the deep snow. These dead snow gum poles were selected and cut (using a 150 g DIY bow saw) to have ~30 mm diameter tops that would fit snugly into the four insulated stainless steel stove mounts. These mounts are loosely pinned (at the campsite) to low profile clevises that are welded to the stove body. The clevis and pin hinge arrangement allows considerable flex in the stove mounts so that they can align themselves with the irregular orientations of the bush mounting poles. Having removable mounts makes the stove body a ‘pack-friendly’ shape. 

Stove assessment

The lager slim oval ultralight tent stove packed nicely in my backpack and it was a great success in keeping us warm and allayed my concerns about the failure of the field test in front of the group. The larger cooktop could easily heat multiple pots. The larger stove body seemed to have a lower temperature than the smaller stove, but it also seemed to radiate a lot more heat and the flue pipe temperatures were much less (only 100 degree C at ~500 mm from the stovetop)  than those on my smaller tent stove.  The flue pipe was not uncomfortable to touch where it was about to pass through the flue gland. This means that the larger stove is probably more efficient at radiating more of its heat into the tent. The larger stove burnt 410 g/h of wood which is only marginally more than the smaller tent stove. The 60 mm dia fuel tube (c/f 50 mm for the small stove) provided easier fuel loading, allowed the use of thicker fuel sticks and provided a more stable burning.

The stability of four leg mounting of the stove was better than the one leg design for the smaller stove and there was no concern with the cooktop sagging when a big load of cooking was placed on it. My companions repeatedly commented on how clear the flue emissions were, there was seldom any sign of smoke and this meant that the combustion was clean. complete and efficient. The stove sometimes made a gentle chuffing sound that on one occasion coincided the distant sound of a helicopter, but it was by no means unpleasant. Once started with some dry sticks, the stove worked well with directly collected dead snowgum sticks that were quite cold and damp.

Deficiencies that were revealed were that the flue pipe needed to be anchored down to the stove body so that it could not be bumped off. The fuel stick/burner tube needed a more substantial mounting.

There was an occasional problem of the burner becoming choked with ash and charcoal, but I think this could have been due to the inadequate connection of the flue pipe.

Under the cold conditions the stove was a little harder to start and with a snow pit and wearing stiff ski boot it was difficult to get down to gently blow into the primary air port (as I usually do). A USB fire blower should be a useful tool to deal with this situation.

Lastly, the stove would probably be better mounted on only three legs (rather than the four as in the photos) as this would make the mounting much easier and just as stable. Luckily the stove has six possible mounting clevises on it so this should be easy.

Tim

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