Make an Ultralight Tent/Tarp (556g) - Part 1/3

Part 2, Part 3, Ultralight Tent Pictures, Ultralight Tent Pegs, DIY Short Tarp Pole, DIY Long Tarp Pole, DIY Carbon Fibre Tarp Poles

Background

In 2006 I threw all my ideas out of the window about what I 'wanted' from a shelter. Instead I looked at it from the viewpoint of what did I actually need from a shelter. There were a lot of myths knocking around about what would and would not work in the UK and some of these myths were based on camping technology that existed 10 or 20 or more years ago.

In various settings and under various weather conditions I have now tested Gore-Tex and conventinal bivy bags, Shaped tarps, flat tarps, tents and nothing at all.

Gore-Tex bivy bags are great for the harshest of conditions when a tent-like-thing is not possible but condensation in some form or other always seems to be at least a minor issue. Bivy bags do on the whole seem to be very warm but when it rains all you can do is lie there and inhale your own breath - and it is the breath that is the cause of the bulk of the condensation.

I do like Bivy bags for some trips simply because they can be placed anywhere and will survive any weather. They are slightly more tolerable in bad weather if used with a micro-tarp but for most people a Bivy bag is best thought of as a 'just in case' weather protection.

WIth tarps I find that whilst condensation did sometimes occur on the underside of the tarp it was not bad enough to be anything other than mildly irritating. Yes if I touched the tarp I would get a little wet but it wouldn't stop the fabric working.

I found that a tarp was very flexible in where I pitched it and how I used it and if strong winds were not expected I could create a very large dry area for a little weight. With very rough weather it was necessary to pitch a square tarp quite low and this reduced the headroom and the fun.

If rain is not expected (it can happen) I have found that just sleeping on a groundsheet (or outside of a bivy bag) seems to be the best option. If there is no 'weather' there is no need for shelter...

With tents I found that the lightest one that I own (at 1.6Kg) did give me a degree of extra weather protection - providing that I could find a place to pitch it.

When I looked at the weights of all the different options then the actual variation is not that great. A Gore-Tex bivy bag can be classed as a complete shelter and will weigh in around 700+g. A 300-500g Tarp will require a groundshee and/or a bivy bag of some form which will add 100-500g of weight and so for practical purposes their is not real weight difference between Tarps, Bivys and the very latest ultralight tens.

Finally I have to say something about bugs and other small flying critters. In some parts of the country and in some parts of the year they are a major issue. For the rest of the time they are at most a minor irritant and choice of camp location can resolve most issues - as can weather. Wind and rain will see most of them gone...

Design Considerations

Weight and Condensation

After lots of field testing (and some disasters) I concluded for me that most of the time I would be be best served by some sort of durable tent-like-thing for a given weight and I would reserve the use of a Bivy bag to trips at higher altitude.

When I looked at the weights of fabrics and the actual cost (in weight) of a double-skin tent I ruled it out. Touching a damp Sil-Nylon fabric may not be fun but that is all. It will not affect the performance.

Condensation in reality is only a major issue when there is no airflow to the underside of the fabric and at the same time their is a source of water vapour under the fabric - either from me sweating or from the ground.

If there was good airflow then all the condensation problems disappeared - beyond perhaps a very slight sheen on the fabric interior sometimes - but no major droplet formation.

I ran through several design concepts of ways to place some sort of bug-net/groundsheet combination under a conventional tarp but the weight always crept up into standard tent territory for no real benefit. [Tarps in the UK]

I tried a few variations of a fully-enclosed single-skin tent but even with a fair bit of creativity could not achieve sufficient airflow through the tent to prevent severe condensation.

I did look at using breathable fabrics but the weight penalty for them is huge. There is also a design fundamental that the inner tent surface will be a natural condensation point and there is [I thin] insufficient heat-differential to drive the vapour through the fabric - unlike in a jacket or a bivy bag.

After playing with a lot of designs and with the experience gained through the failed prototypes I concluded that the optimal weight and fabric utilisation would be achieved through using a contoured tarp with bell-ends and a separate Bathtub floor groundsheet.

So far the prototype has proved very successful.

Sleeping Bags and Mats

Built into my design considerations was the construction of modern sleeping bags. All of my multi-season sleeping bags have a pertex outer of some form. They are more than capable of coping with condensation or the occasional drop of water - they do not need special protection.

There is however an issue that some bags are much less resistant to wind than others and of course wind has a large effect on the perceived temperature. This just comes down to choosing a bag for the conditions. My winter bag is windproof/showerproof and works very well with a tarp. My other main bag has a water-resistant pertext cover but is much less windproof in reality.

I have slept outdoors in just a sleeping bag with no cover and woken up to discover that whilst there was condensation on the footbox (where my feet were not) the bag was still functional and warm.

Fundamentally bags do need some protection from the elements but not as much as you might think and certainly not as much as they needed 10 or 20 years ago.

Price and Durability

The very lightest fabrics achieve much of their lightness by a loss of durability which in turn means that they are much more fussy about how they can be safely used. If you always have to carry an extra ground-sheet to go under your shelter then you have to ask if it would have been better to design in a stronger floor in the first-place (sometimes yes, sometimes no).

The very lightest fabrics also tend to be the most expensive. To give you some examples the lightest Tarp that Bozeman Mountain Works produce is 100g (fabric only, no pegs, no poles, no guys) - but it is is very small, delicate and expensive. It also HAS to be used with a bivy bag in bad weather - the lightest of which is 130g.

So at the extreme lightweight end of the market it is possible to have a complete shelter system for under 300g which would fail under some weather conditions and would require careful choice of site and shelter to be usable. It would also only barely cover a single body.

My choice was then to use cheaper, heavier and more durable fabrics that would withstand a good amount of weather and provide a reasonable amount of coverage for one person.

I can always reduce weight by reducing the amount of fabric used or by using lighter fabric. Each one involves a trade-off.

Fabrics

The natural choice for the tarp was SilNylon (Silicone-coated-nylon) which is available from some specialist UK retailers such as Point North Fabrics or Pennine Outdoor.

SilNylon is amazingly strong and 100% waterproof. It also does not sag when wet. If you add in to that the fact that it is up to 5x stronger than PU-coated nylon of the same weight and it all adds up to a no-brainer.

The only downside of SilNylon is that it is amazingly slippery and a total bitch to machine.

For the bathtub floor I chose 2oz PU-coated ripstop nylon. This is not as waterproof as SilNylon but is a lot cheaper, about the same weight and has much more grip to it. It is very boring to slide around all over the tent becasue a pitch is not perfectly flat.

Since the groundsheet is not integral I have the option to use a heavier and stronger groundsheet if I am expecting bad terrain. I also have the option of not pitching the tarp at all if the weather is good.

Bugs

I am still in two minds about Bug protection. Most of the time I think it is unneccasary.

A full bug 'inner' tent is quite expensive in terms of weight. A bug-skirt as used in many of Henry Shire's TarpTents is an excellent compromise but would still add weight (and a lot of extra sewing).

The possible alternatives that I am looking at are something like a 1m mesh pyramid (80g?) that can be fixed onto the front of the groundsheet and a very big mesh headnet (40-60g) that could be placed over the head or placed over the top of a sleeping bag.

The fundamental design consideration is that bugs only like flesh and are indifferent to packs, bags and assorted kit and so the only thing that needs protection is flesh. The UK is not a mosquitto country and so in general small bugs are an irritant rather than a health risk.

Geometry

The one thing that restricts the use of a tent on a variety of sites is that it is forced to have a fixed shape due to both ends being enclosed.

I wanted to have fully enclosed ends on the tent for weather protection and I also wanted some space where I could (just about) cook.

However, if the weather was going to be nice I wanted to be able to open both ends and be able to see everything or conversely pitch really low in bad weather.

The result of all these consideration (and to minimise the use of fabric) I decided to go for a tapered tarp with front and rear doors.

The Tent - Pictures

Here at last then is some pictures of the tent.

• The poles are pitched much closer than usual to the tent in this shot. Pitching further out provides much better fabric tension.
  
  
• The ridgeline has several loops sewn onto it at various spacings. This emulates a caternary ridge but wit h a bit more of flexibility over pitch and tension.
  
  
• The front pole is under a lot of tension in this picture but is under dynamic tension from 4 directions - and so in reality is not about to go anywhere. I would normally have a trekking pole or a tree to tie to.
  
  
• The sides are clear of the ground to allow good airflow. The bathtub floor has deep sides to prevent rain ingress and to encourage airflow over the interior of the flysheet.

• The Groundsheet has deep sides which are shown clearly here.
  
  
• The Groundsheet has several pitching options including pegs and tension guys. The left side shows a tension guy being used and the right side a big peg.
  
  
• With both front and back doors open cover is still generous but the views are much better.
  
  
• Minimum configuration is 6 pegs - one on each guyline and one on each corner. Additional pegs can be used at half-way point on flysheet and on the doors at either end as well as up to 4 on the bathtub floor giving a maximum of 12 pegging points for really bad weather.
  

The Tent - Actual Weights

Finally we come to the weights of the finished tent. Not bad for a home-made effort is it?

Part 2 explains how to make the bathtub floor.

Part 3 explains how to make the flysheet.