I have been selling these, but at present have ceased production as it wasn't economic. Things may change.
For winter use the tent design has to be a tunnel with a double skin. A tunnel rather than a dome because the tunnel is more stable; a double skin to keep the snow out. Yes, this means that 'winter' really does put the focus on snow use. For ordinary bushwalking in winter at moderate altitudes the summer tent would be fine. If you are intending to be above the tree line a lot, then it's a toss-up. I use my summer tent in the Australian Alps above the tree line, but I select my sites with some thought to wind.
The first version used three hoop poles and is called the 'orange' tent. It can also be seen on the Ultra-lightweight page and the Stove page. The orange one in the pictures uses the NASA fabric, but the design works just as well with the silnylon fabrics. It has to use pre-bent aluminium poles as the radius of curvature needed is way below what can be safely done with straight aluminium or carbon fibre poles. You can use straight aluminium poles, for a while, but this takes the poles a factor of about three beyond their elastic limit and eventually results in a fracture - I know!
If you want to use carbon fibre poles, as I do in the summer tents, you must use bends. You simply cannot put this much bend into them without a failure (but the forces would be quite high!). I have therefore upgraded this winter design to take carbon fibre poles. In the process I have increased the number of bends to three per pole, as for the summer tents, and I have also increased the number of poles to four. This gives enormous stability in bad weather. In due course I will get a picture of this new design here, but some details are given here.
As you can see from the line drawings below, the tent uses four poles or hoops to get its characteristic shape. It has an inner tent of similar shape to stop the wind and the snow. Is it symmmetrical? The tent shown in the picture above was the 'orange' prototype and is almost symmetrical - the doors themselves were slightly different but this is not visible here. We found in practice that it was very easy to always use the end with the better door design as the main entrance and the other as the pack store. For this reason the end bells are now made slightly asymmetrical, with the 'rear' end designed for packs and the 'front' end designed for living and cooking.
Some much simplified line diagrams for the tent are thus. The green rectangles represent 3/4 length air mats, and the red ovals represent bodies in sleeping bags - bodies of about medium height. The funny corners at the top ends in the side view drawing are the storm hoods over the windows at the tops of the doors. Even with the windows open (essential to prevent condensation), heavy rain does not come in.
These show the outline but not the pole shape. The next drawing shows that. The weight of this version using silnylon and carbon fibre is about 1650 grams, which is lighter than the orange tent at about 2kg. An approximate weight schedule for the materials is as follows. It is interesting to note that the four carbon fibre poles weigh less than the three aluminium poles in the orange tent. Most of the notes for the summer tent are generally applicable here too.
| Item | Description | weight per | Weight | |
|---|---|---|---|---|
| Fly | Silnylon | 49 gm/sqm | 503 gm | |
| Inner Tent | DWR breathable nylon | 32 gm/sqm | 342gm | |
| Netting | Knitted | 19 gm/sqm | 30 gm | |
| Groundsheet | Silnylon | 49 gm/sqm | 206 gm | |
| Poles | Carbon fibre, SS bends, Al joiners | 34 gm/m | 310 gm | |
| Zips | Nylon coil #3 | 12 gm/m | 104 gm | |
| Sundries | Thread, bungee cord, Velcro, etc | 150 gm | ||
| Total | 1646 gm |
This design is not frozen either. It too has been described mathematically (conic sections etc) and can be varied.
Both the silnylon (49 gsm, 60 kPa) and the orange fabric (55 gsm, >100 kpa) are nice, and both are very slippery, so snow will slide off them very easily. This is better than local tents which have a nylon fabric outer surface to which the snow can stick. However, after several snow trips I found the orange fabric had problems. The thick orange PU layer you can see in the photos gets very stiff in the cold, and the nylon fabric on the inside can absorb water and get heavier, and even freeze. I have since switched entirely to the silnylon fabric. This does not absorb any water and has a fantastic temperature range.
The inner tent has to be spaced a little inside the fly to avoid having them stick together. This can happen under conditions of high humidity and falling temperature, which can cause some condensation on the inside of the fly. I initially tried a spacing of 50 mm, but this was too little. I found there could be contact under severe weather conditions - just when you really don't want any problems. I favour a spacing of about 70 - 75 mm. Adding 25 mm to the height of the outer tent seems a small price to pay for the improvement. Yes, I made the outer bigger rather than the inner smaller: we value our headroom and living space, and the extra weight this added was pitiful.
The inner tent is attached to the outer tent by Velcro joiners at each arch. I use a narrow Velcro but quite a few joiners, and this gives me a good curve with no sags on the inner tent. These links can be adjusted to get optimal tension, and do allow you to separate the two for repairs. I do not advocate splitting the two for packing: that's a complete waste of time.
The doors are located at the poles and go down to the groundsheet. You will notice that the poles lean outwards, so the entire door is outside the groundsheet. This is different from many dome designs which have the door over the groundsheet (raving idiocy!) and ensure any drips land on the ground, not your groundsheet. The inner tent door is made of the same fairly windproof fabric as the inner tent, and is closed with a zip to keep snow out. Just outside this inner door there is a netting door. You can have the windproof door open and the netting door shut in fine weather: standard stuff.
The length of the inner tent is slightly less than the distance between the end poles. This allows the Velcro joiners to exert some pull lengthwise, which keeps the inner tent fairly taut. You don't want the inner tent flapping around.
The orange prototype shown used a white medical material (80 gsm) for the groundsheet, but this was overkill. The coating was fairly heavy (and good), but the fabric was no stronger. You do not need a high pressure rating in the snow: any water at floor level will sink into the snow. The worst case is probably when you are pitched on sheet rock without a mattress. I have quoted the silnylon weight as I have found this is quite adequate, and I use it on the summer tents. I assume you will take some care of your tent, but in the event of any accidents repairs are quite easy.
The original poles were a fairly lightweight Easton 0.344" poles at 34 gm/m. These had to be pre-bent, otherwise they would work harden and snap. The 7075 T9 alloy used was fairly reliable; the newer and slightly lighter ones of 7178 alloy are just a bit brittle. The cheaper 7001 T6 alloy found on some other brand poles is weaker, and makes the poles heavier (although the new DAC Featherweight poles might be better). However, the carbon fibre I am now using is very strong and far lighter. With the silnylon fabric it is very easy to insert and withdraw the poles from the sleeves, even in the snow. I use bungee cord inside the poles to hold them together, and short lengths at the pole-ends to tension the roof over the poles.
Other items such as zips, bungee cord, eyelets etc are as for the summer tent. There is a surprising number of little bits involved, and I found that it was really necessary to scrutinise every item to keep the weight down.
© Roger Caffin 6/6/2002