In my previous post, I set out the background to the plan to make my own shelter, and in this post I’m going to explain the design itself, explain the process of designing it, and the decisions that have been, or will need to be made along the way.
The aim of this post is partly to show why designing your own shelter need not be a daunting process. It just needs a few stages and the discipline to stick to them.
First, it’s important to make sure that we understand our requirements, because if we’re not clear about what we want, then how can we hope to end up with what we want ? And in setting out the requirements, it’s important to not think too much about the solution – the key is to really understand what we want it to do rather than how it does it. (oops, sorry, a bit of the “dayjob” creeping in there).
I’m going to separate the requirements into two parts – how I want to use the tent, and specific physical characteristics it needs to have (e.g. size).
- I need to be able to use it through 3 full seasons – so from early spring to late autumn. I’m not looking for it to be a winter shelter, although if it proves up to the job, I’ll happily take that as a bonus.
- This means it needs to be capable of coping with reasonably sustained periods of rain and wind. So it needs to shed wind efficiently and provide enough cover, whilst maintaining as good ventilation as possible.
- I need to be able to close the shelter either to keep in warmth, or to deal with wind-blown rain coming right at the door area.
- If the tent is closed fully, I need to have enough space inside to cook and to be comfortable.
- Conversely, in nicer conditions, I’d like to be able to open the tent up for maximum airflow and views. But I’d also like to be able to cope with light summer rain which means keeping the tent open but my stuff covered.
- I need to have some flexibility of use in terms of sleeping arrangements – the ability to have a light bugnet inner, a more windproof part solid inner, or no inner at all.
- On a long distance backpack, I might sometimes need to camp in lowland and to hide. It needs to be a stealthy, or at least restrained, colour, and to be able to fit onto the smallest space possible.
- The shelter must accommodate an inner 230cm long, 80-100 cm wide and 115cm high, that has a vertical bathtub of around 10-15cm.
- The shelter should pitch with a single trekking pole at a height of 120 – 135cm.
- The shelter must include a vent, and therefore, not just rely on open doors for ventilation.
- It should be possible to pitch the tent all-in-one (ie with inner attached).
- Doors must be able to hang to the same height/ground clearance as the rest of the fly.
- Doors must be able to be pitched in an open configuration to increase ventilation whilst still able to deflect some weather.
- The inner floor should be robust enough that a separate groundsheet isn’t needed.
- The tent should include additional mid-panel or mid-seam tie outs.
- The tent should have reinforcement at all stress points. Specifically, that reinforcement needs to have similar stretch characteristics to the main fly fabric.
- The tent should be as light as possible, without compromising on robustness.
I’m sure many reading this post would come up with similar lists of things they need from the tent. The above requirements basically form a checklist that the design needs to conform to. A tent design that meets all of the above, will by definition, give me what I’m looking for.
The previous post, will have given you a good idea of the style of shelter I’m looking for. Clearly my experience with that genre of tent has informed the above requirements, so it’s no surprise that the design fundamentally looks to achieve that style.
So I knew at the outset roughly where I’m headed in terms of overall shaping. It was then a matter of achieving the right balance of the other things.
Design – Overall Shaping
Because the size of the sleeping space is central to my requirements, I designed the shelter by working from the inner dimensions, which I was already very clear on, and moving out from there.
The key here was to look to emulate the sleeping space of the Lunar Solo/Lanshan type of shelter, by making the inner at least a minimum width, and then extending it at the rear to a wider point. I use this as my storage area, leaving the main rectangular part of inner as a sleeping space. It also means I know where to find things, as everything’s in one place rather than dispersed around the inner.
So the inner is a pentagon – imagine a rectangle where the mid point of one long side is pulled away from the shape to form a point.
In turn this means the back of the tent also forms a point at the back, directly in line with the rearmost point of the inner.
Adding an appropriate extra to ensure the fly clears the walls of the inner, then determines the overall length of the tent, and how far back it protrudes. But this is also determined by how high the vertical part of the bathtub is, as the sides of the inner only start sloping from the top of that. Basically the higher the bathtub, the longer the tent needs to be, or the higher the pitch. I have designed the tent based around a “to the floor” pitch of 120cm high to ensure that everything clears adequately. In practice, the fly will never be pitched below 125cm, and so there will always be more clearance than the minimum. This also allows for pitching on uneven ground.
Next I added on some space in front of the inner to form a permanent vestibule. Most tents of this type don’t have this, and the doors start from pretty much the front of the inner. I was very clear that I need a bit of a gap in front of the inner. It’s not huge, but I don’t want to make it too big as most of the time I’ll have the doors flying open anyway so don’t need loads extra. It just needs to be big enough for when fully closed. I can also pull back the front corner of the inner to make some extra space to cook safely – this is another reason for making the inner reasonably spacious.
The bathtub height is also partly linked to the expected ground clearance of the fly itself. If I’m always going to pitch the tent at 125cm (so with 5cm of ground clearance all round), I want the bathtub to be at least 5cm high so that any wind blown moisture hits the waterproof part of the inner. Indeed, I actually want the bathtub to be higher than the ground clearance so that there is some overlap. Given that I will also in finer conditions pitch at 130cm, and so have up to 10cm of ground clearance, the bathtub height needs to be more than 10cm.
I initially looked at a bathtub height of 15cm, but found that scaling it back to 12cm allowed me to shave a bit of footprint off the tent overall, and importantly to ensure that every fly panel had at least one side that fits the width of the fabric I’m expecting to use. This makes it easier to fit the shapes and plan how much fabric to buy, as well as ensure I’m working with the weave of the fabric itself.
Now to add some height – first by completing the upper ramparts of the inner itself. I’ve already said I’m aiming for 115cm high at the peak of the inner. 12cm of this is the bathtub height, so we add 103cm further height at the highest point and the inner then falls from this to each of the corners at the top of the bathtub.
Completing this, I then add the extra distance to the peak of the fly – a minimum of 120cm, so 5cm more. This is to check that everything works when it’s at its most hunkered down – any pitch height above this simply separates the fly from inner by more.
As you can see, a pitch at 120cm is tight, but I’ll never go that tight in practice. The sides of the inner will also sag a bit in practice, so there’s actually more safety margin than there seems.
You can see that just adding 5cm to pitch height improves the clearance noticeably. And I also have the option of going a further 5cm higher.
In an extreme I could go yet another 5cm higher. This will be enough. Sometimes, I could be using a shorter inner anyway, in which case the problem is irrelevant.
So the above steps got me to the basic design of the main bulk of the tent, sufficient to ensure I have the space I need for sleeping without going excessive in terms of overall footprint. The design now looks like this, with a bit of colour added:
Design – Up Front
This was the hardest part, as this is the focal point of quite a lot of my requirements. It’s relatively easy to design a shape of a certain size, that will always be pitched in that exact shape. The front however, is critical since:
- it contains the only moving parts of the shelter (doors and vents)
- it still needs to contribute to the overall weather handling properties of the shelter
- it’s the part of the tent that ultimately defines the profile and look – it’s aesthetically important
- it’s the part of the tent I’ll “use” most
I said in my previous post that the aim was for a door arrangement that can be pitched to the same level as the hemline of the tent, but which can also float a bit like a small canopy (like in the Lunar Solo). However, there is one important addition before we start shaping the doors.
I wanted to have a beak so that when fully opened up, there is still some amount of protection. However, I don’t want this beak to be so big that it creates an entrance tunnel (think Trailstar here). I can’t be doing with wriggling into the shelter – it needs to have enough door height for a dignified entry and exit.
Getting a beak that meets this delicate balance was essentially a matter of pure trial and error. I had to play about with the angle of slope, how far it protrudes and how much height to have under it. I finally arrived at the following:
The beak height is 94cm from the bottom of the tent (so in this 130cm pitch, a total of 104cm from the ground). The beak centre line being 43cm long. The end of the beak is flush with the front line of the tent. The beak slopes at approximately the same angle as the rear centre seam of the tent.
This leads to a very noticeably asymmetric shape overall. It will be important to pitch it so the rear takes all of the nasty weather. The front is designed for more pleasant times!
Design – The Doors
The moment that I can’t put off any longer – shaping the doors.
I already know that I’m going for an overlap design to eliminate the zipper. For simplicity, each door will attach to the opposite beak – e.g. the right hand door as you look at the front will have its left hand edge attach to the left part of the beak. This means that the overlap will be essentially the gap between the sides of the beak. The question then is how far down the beak to come – the further down, the greater the overlap.
It will be obvious that this approach leaves a triangular gap above the doors, and there are no prizes for guessing that this will be used to create a vent. So there is an extra consideration – getting the balance between door height and vent size. The diagram shows what we get with starting the doors 15cm from the top point of the beak. I may need to increase this though – this is one of those things that I need to see in the flesh on the prototype. I suspect I’ll make it a bit bigger, which will shrink the door height accordingly.
Both doors will then swing up and outwards to create a flying beak/canopy. I may need to adjust the shape of the vertical door edges to make this look right – the idea is that the corners of the doors should be pretty close when “flying” – this is important as they will attach to the same guyline.
This guyline will run from the top of the beak, down over the top of the vent and to the ground some distance in front of the tent. The doors when “flying” will then attach to this guyline.
In most conditions this will be enough protection itself, and will also allow ventilation under the doors. It should give enough space under shelter to cook, move around etc.
The vent won’t be unprotected – it will have a (section of) conical hood that will overlap the top of the door. Aesthetically, I want this as small as possible, and so this is another aspect to judging the vent gap itself. The vent may also squash down a bit when the doors are “flying”, which will be fine.
When I build the prototype in cotton, I’ll start with doors at the height shown, and if I feel I need more ventage, will simply trim a suitable length off the top of each door until I’m happy. The hood will then be sized to provide coverage against wind-blown moisture. I’ll update the actual door and vent sizes in a future post after prototyping.
Design – Other Elements
Reinforcements – Each corner will be reinforced with a suitable fabric and for simplicity I’ll aim to pick something that works for all reinforcement points. Ideally the reinforcement fabric needs similar stretch properties as the main fly fabric to prevent shearing along the stitch lines.
Tie outs – the intention is to attach these with webbing. Additionally, I may try to incorporate the inner attachment points into the same thing.
Inner attachments – I haven’t yet decided what to use here – it may be mitten hooks, or I may see if I can do something with linelok side release buckles if I can find any lightweight enough. These are like a standard side release buckle (think rucksack hipbelt closure) but one side has an integrated linelok. This means I can use cord rather than webbing on one side, and this will be the side that actually attaches to the inner.
Peak guyline – this will be attached with webbing to the beak, or I might see if I can integrate it into the inside of the tent peak (where the inner hangs from), and run it out through the vent. Either way, the doors will be able to attach to it when “flying”. I haven’t quite figured out how yet, but have seen some examples of that sort of thing (not least on the Lanshan).
Corner guyouts – these will be lineloks. If I’m putting webbing on the corners anyway for guys, I might as well give myself the flexibility of having lineloks there.
Guyline – this can be thought about and played around with later, but I’ll be aiming for 2.5mm to 3mm for the key lines and anchoring points. I’ll use thinner 2mm for mid panel tie outs as they’re more about gently maintaining shape rather than fundamental anchors themselves. I haven’t yet decided whether these will be truly mid-panel or whether they’ll work by embedding half way along the seams. This is something I can better visualise on the prototype, but I suspect that the shape of the tent means I’ll need to go for mid-panel.
Inner – this will be a mixture of mesh and solid fabric above the bathtub. Doors will be inverted T zippers so that I have flexibility to open up either side or the whole thing. Corners of the bathtub may just be left to be formed by the guying of the inner, although if I need to enforce the shape I’ll use some thin light rods of some kind. Will probably go for something like 1.6oz HyperD for the floor. It’s probably fair to say that I’ll make the inner last – I already have inners that will fit.
Zippers – due to the overlapping door design, the fly itself won’t need a zipper. The inner doesn’t need anything fancy like a water resistant zipper, so will be looking at bog standard zippers, I guess #3 or #5 size. I’ll work it out in due course.
Securing the doors – With no zipper to hold the doors together, I will need something at the bottom (where they overlap) to keep them in place. This needs to be easy to undo and redo for entry/exit. I’m thinking more linelok side release buckles here. Ideally, I’ll attach these such that they’ll do double duty for the attachment to the peak guyline when in “flying” mode.
Fabrics – I already talked a bit about this in the first post. I’m probably going to build this in 1.1oz Silpoly, which with coating weighs about 1.24oz/yd2. That equates to 42g/m2. The stuff Ripstopbytheroll sell is 20D x 20D coated both sides, and comes in a decent range of colours. I’ll probably go with Dark Olive or Charcoal grey. I’m expecting a weight in the region of 350-500g depending on fittings used etc.
I said at the start of this post, that is was important to understand your requirements, so let’s take a look at whether the above design will meet them:
|Reqt No.||Requirement||Met ?|
|1||Full 3 season use||Yes|
|2||Shed wind and rain, but still be ventilated||Yes|
|3||Fully closeable||Yes, doors down mode|
|4||Enough space to cook/be comfortable in closed-up mode||Yes, extra vestibule|
|5||Open up for airflow when nice||Yes, “flying” mode|
|6||Flexibility of inners etc||Yes|
|7||Stealthy/restrained colour and modest footprint||Yes, Dark olive or Grey|
|1||Accommodate 230 x 80/100 x 115cm inner with decent bathtub||Yes, whole tent designed around this exact point|
|2||Trekking pole pitch at 120 – 135cm||Yes, works anywhere in this range|
|3||Has a vent||Yes|
|4||All-in-one pitch possible||Yes, will choose fittings that make this possible|
|5||Doors down mode||Yes|
|6||Doors “flying” mode||Yes|
|7||Robust inner floor||Yes|
|8||Mid-panel/seam tieouts||Yes, exact positioning to be decided when prototype built|
|9||Reinforcement of stress points||Yes|
|10||Light without compromising robustness||Yes|
The next post will aim look at the initial prototyping, and starting the process of assembling the materials, equipment, and sewing skills needed for the project.