myog mountaineering cuben tunnel tent?

[Rog Tallbloke]

Pierre, maybe this firm can help with info
http://www.mountainhardwear.eu/Atlas-Poles/AtlasPoles,default,pg.html

I'm going to dig out my collection of cf golf club shafts and do some weighing/thinking.

[Roger Caffin]

Hi James

> Exped uses straight aluminum poles for the Serius/Aeries series. They are about 10mm or so.

The Sirius tents use DAC Featherlite 9 mm poles. That's a softer alloy than the 7075 T9 alloy in the Easton poles. I think the same applies to the Aries (which I reviewed). And those poles do take a curved set after a while.

Yes, I managed to curved the Easton 7075 T9 poles for a tunnel, but they eventually work-hardened and broke at the top. Precurve is smart.

Cheers

[Roger Caffin]

Hi Rog

> > "I doubt you can bend CF tubing tight enough for a real tunnel design"
> Fibreplex seems to manage it.

That's a 2006 article: 8 years old. The Fibraplex poles are a rolled fabric, which is inherently softer/weaker than the 2D poles I favour. In those days the Fibraplex poles were quite soft indeed. I chose to not use them because I thought they were not strong enough.
My understanding is that Fibraplex has improved the manufacturing process these days so that their rolled-fabric poles are now stronger/stiffer – but they will never be as stiff/strong as a 2D wrap. That's inherent in the design.

Hum – interesting thought though: just how far could one push the rolled fabric poles thesed days?

> a generous 46" of headroom … Too tall! I hear you cry,
Well, no, that's a design and application issue. If that's what you want, I will not argue. The sleeve will reduce the internal height a bit, and with that height you can easily have a good 3" air gap between inner and outer – nice.

We just want photos!

Cheers

[Rog Tallbloke]

More great info, Thanks Roger C. So the latest fibraplexes might not like doing a tight radius without elbows. A single elbow might work though.

I'm beginning to think I need a few pole sets for my planned tent, ranging from ultralight cf for bragging rights on UL forums, up to some strong precurved alloy poles for going high in winter.

At the moment I have my ebay eye on an early model Vaude Ferret (3.4Kg !!) for motorcycle camping plus pole donor. As far as I can tell from the photos the poles look to be at least 10mm diameter. :-)

> We just want photos!

I'll try to find time to make a tyvek mockup this weekend. I'm not cutting my Cuben until I've measured several times and made some tyvek patterns to consider.

[Roger Caffin]

> So the latest fibraplexes might not like doing a tight radius without elbows.
You know what my answer will be, don't you?
Buy, bend, and maybe break.
Mind you, Tom at Fibraplex may be able to tell you what his recommended minimum bend radius is. That would be worth knowing. (ie, let him do the break bit on his wallet!)

> I'm not cutting my Cuben until
Caffin's Law: Field testing starts with V6. Mind you, with the stoves it was more like V26…

Cheers

[Sam Farrington]

The Gold Tip Expedition Hunter 7595 layered arrow shaft is a little lighter, stronger and more flexible than the Victory 400. When Mountain Hardwear and GoLite came out recently with their lower denier nylon hoop tents, I tried flexing the Gold Tips in place of the alloy front hoop poles, and they bent readily to the required radius. (Ferrules were from Easton Injexion shafts with .244" OD.)

The photo of the Fibraplex poles is surprising. Some purchased around 4-5 years ago would not bend to anywhere near such a small radius. So maybe there has been some major improvement with strength and/or flexibility. Too much flexibility, however, will make for an unstable structure, as with the discount store tents with cheap fiberglass poles.

In any event, elbows are not necessary. One or two sections at the center of the pole can be alloy, and prebent to a slightly arced or crescent shape to relieve pressure enough on the rest of the pole made of carbon tube so that it is not overly stressed. In effect, the center pole section(s) become very long flexible elbows. An alternative is to use filament wound fiberglass tube for the center section(s), as while strong, it is more flexible than carbon.

This is somewhat of a drift from the original post's premise of using cuben for a tunnel. Having followed the discussions here since cuben first came out, and corresponded at length with one cuben tentmaker, I still have not found a way to bond or sew, and seal any variety of cuben to create a strong and waterproof seam that will not leak or peel apart on a tent. So I think a tunnel would have to be redesigned somehow for cuben. Perhaps with pole sleeves limited to each end of the tunnel, with the other pole(s) inserted into the tent after pitching, as Oliviere did in his posts here a few years ago about a highly wind resistant tunnel tarp used in Iceland.

But I appreciate Pierre's tests with the cuben pole sleeves, albeit for me, the results don't provide much comfort, especially where unlike the stresses on a tarp, the pole sleeves will inevitably create stresses on the seams to peel apart. If the tent is to be used for mountaineering, in exposed areas with high winds, I suppose the heavier 1 oz cuben with the thicker mylar (.18) would be desirable. This is pretty close in weight to the 1.12 oz of the higher quality 15-20 denier silnylon used by Terra Nova on its tarps. So the weight saving from cuben appears marginal, and the nylon can be sewn with strong lapped seams and sealed effectively. Perhaps the real issue is whether the cuben will form a stronger structure, despite its lower elasticity and the need for seams that will not peel apart. Such a conclusion seems difficult to reach from reports in this and other related threads.

The cuben appears to be less flammable, though, and gasoline or petrol powered stoves often used in mountaineering can flare up and do a number on a silnylon tent. For wilderness backpacking though, nylon appears preferable, at least until we can be assured of joining cuben with seams having as much resistance to peeling apart as a sewn nylon lapped seam.

[James Marco]

Roger, yeah, well after ten years of use I figured they had a right to be tired;) Most of the pole sections I use have a slight radius (like 1/8" per foot) these days.They were shipped straight, though.

I agree about the T9 poles. They are likely to hard to hold after a few uses without precurving them.

I had some trouble about 12 years ago with the tip/junctions splitting. Exped sent me a new set that has held up for more than ten years. They used to include several splints, 2 with the poles and two in the tent mounts. I think they knew this would be a problem. They replaced the poles with no questions asked.

[Rog Tallbloke]

I've got as far as making a scale model of my tent design in paper. I'm leaning towards a geodesic support structure totalling 14 x 2-section 1m poles, so I think I might go a little thinner, to 7mm or 0.2755". That diameter will plug straight into the inexpensive 3-way ABS plastic joining pieces I've found. The tent will be approximately hexagonal and have a floor area of around 37 square feet and a peak height of 47 inches.

So, I think I need the strongest (heaviest?) .275" carbon fibre arrow shafts I can find at a reasonable price. Beman junior hunters seem to have a good rep. Anyone played with them?

[Roger Caffin]

Hi Rog

Drawings! Photos!
Sounds interesting.
However, I have not used the Beman brand.

Cheers

[Oliver Nissen]

Hi Pierre,

I wish I'd seen this thread earlier! I fear you've been barking up the wrong tree for some time, and I'm hoping you've not cut into your precious Cuben Fiber yet?!

Roger says "I think the fabric stretch is essential to absorb wind blasts. It adds toughness."

I agree, but I think there's more to his line of argument – after all Roger has clearly not persuaded you that Sil-ny is the way to go!

As he says, stretch plays an important role in damping dynamic forces – this helps prevent destructive resonant flapping. Jerky flapping is particularly problematic for snow anchors, plus the flexing it may cause will do worse damage to laminates like CTF3 than would to coated weaves.

Aside from its role in damping dynamic forces, stretch even serves a purpose under the static loads of a well staked out tent – namely in dissipating tension to areas of the canopy that have none.

Now you might think that you've designed the canopy's pattern to avoid any slack in it. But I serious doubt this for two reasons:

1. Putting this all crudely, all pattern design involves seams and panels being shaped to approximate 3D shapes. Under tension stretch fabrics will conform to shapes by always trying to span the shortest distances they are being pulled across. Conversely, stretchless fabrics will only take a loose approximation of that shape and you'll get sharp variations in tension unless enough seam lines are created to closely mimic the shape that a stretch fabric would naturally achieve.

This evident in this simulation of a row of canopies:
http://ltwsas.com.au/wp-content/uploads/2013/02/fea.jpg

Those appear to have single seams and appear varyingly successful. Where there's bright pink, strategically adding seams would help balance out tension.

2. Tent posts are never placed on perfectly flat ground. The tent posts won't be level and there will be some torsion across the tent and your central canopy. Sil-ny copes admirably with a bit of twisting, while Cuben Fiber will instantly show ripples running up the bias all the way across the canopy. Bad news.

To see best practice in canopy design don't look to tent design, look to textile/tensile architecture. In textile structures it's quite rare to see arched tunnel forms and where you see them you'll either see use of stretch fabrics or you'll lots of seams to create the shape:

Non-stretch fabric over an arch – seams and more seams, going for miles (and note the saddle curvature used):
http://www.horserie.com/gb/zoom.php?Nom_rub=Structures+port%E9es+tendues&Photo=tennis.jpg

A contemporary stretch canopy – and ta dah! Gone are the seams:
http://www.basestructures.com/assets/Images/projects/Basket%20Ball%20Arena%202012/Textile%20Architecture.JPG

PM me and I'll try to find you a material I've seen that'll work for testing out your design. It's very CTF3-like but otherwise very cheap (and only good for prototyping, I might add!) If you're interested?

Best regards, Oliver

[Roger Caffin]

What Oliver says about stress distribution is right – you can get ripples even with silnylon. In many cases I find I can eliminate the ripples in silnylon by moving the pole feet slightly – which you can't do on some of those big engineering structures, but the problem may remain with non-stretch Cuben Fiber.

Some experiments are needed, with field testing, to see what can be done. Could be expensive.

Cheers

[Sam Farrington]

The comments about issues with cuben in shelters make intuitive sense; however, one need look no further than Ryan's current article about trekking in the Uintas in order to gain a different perspective. This is an area with very large open and unforested expanses and unpredictable and challenging weather, despite which it is very popular with groups. My first visit there followed loss of life in a Scout group due to a series of thunderstorms that wouldn't quit. Often, the only option is to camp in open, exposed terrain.

It sounds like Ryan's group weathered this area quite well. The tarp shelters appear to be variations on pyramids made of cuben material. They appear taut and do not show any of the wrinkles, ripples etc. discussed in this thread. So it is difficult to see some of the concerns expressed in this thread born out.

But while cuben shelters cannot be dismissed wholesale, issues for the OP remain:

1. The manufacturers of the best cuben 'mids have developed construction techniques that are not openly shared with the MYOG public. Until that happens, success may be elusive.

2. While a full coverage 'mid tarp looks very protective, new issues develop when the design is modified to make a tent. When floors, netting, pole sleeves, awnings and other tentlike features are added, fabric pieces are increasingly subjected to stresses that tend to peel the seams apart. Where a 'mid tarp was stormworthy, a 'mid tent might not be, and a tunnel tent even less so.

3. And even if a consistently taut tunnel or dome shape can be achieved, as with the very expensive 'frog' shaped Terra Nova tent just posted on another recent thread here, there remain the concerns expressed in 1 and 2, above.

If the OP remains determined to proceed, it might be wise first to read Ryan's article and research the shelters shown there. And try to arrange to take a good look at them up close, with a view to construction and how seams subject to peeling are avoided or addressed. One technique I've often noticed on BPL is the use of completely separate screened and floored bug tents supported inside the tarp 'mid, and no doubt there are other techniques as well.

The suggestion to build a tunnel mock-up first of much cheaper material is a good one if someone can come up with a cheap fiber reinforced mylar to use for this purpose.
Even then, cuben itself can vary in terms of bonding. I tried using West System low viscosity G-Flex Epoxy on .5 oz cuben from Cubic Tech, similar to the olive flat finish .5 oz material from Zpacks, and on highly reflective light green .75 oz cuben material from Zpacks. The .75 oz material easily peeled right apart. Attempts to peel apart the .5 oz material easily ripped the mylar right off the top of the cuben sandwich. After fooling around with bonding cuben for several years, that's when I started looking at 15-20 denier sil and PU coated nylons mentioned earlier in this thread. Fortunately, the tent design is much better suited to the elasticity of nylon than the cuben, so it's all good.

[Oliver Nissen]

Hi Samuel,

I felt my essay was getting too long so I removed my final comments, but kept a copy of them for a moment like this. Perhaps this clarifies my misgivings with particular uses of Cuben Fiber:

IMHO CTF3 is excellent for triangulated forms, in particular when you can adjust the position and tension on each of the corners. Pyramid tent and tipis – excellent choice. Geodesic, quasi geodesic and cross-domes – I'm awaiting 1st hand experience. Tunnels – I'm most doubtful here.

I've got a Cuben Fiber pyramid (a lovely Khufu) and it's withstood a whirlwind passing directly over. But I only think the Cuben works because I can reliably get the 'mid really taut.

[James Marco]

I agree that the ends may be a bit difficult to tension properly with cuben. But it is NOT impossible. Nor is a triangular section required to stress the ends, though you end up working with conical varients and perhaps wasting more materiel than would otherwise be needed during the cutting out.

The body is not that difficult. It is simply a 3 dimensional structure that will require little involvement from the user, other than correct calculations for height, width. Length becomes a matter for infinite adjustment with the load desired and number of poles. This can be ignored since it is a simple half tube.

The ends are the same, ignoring the entrance way. These are based on a cone laid at an angle to the ground. It becomes a simple excersize to calculate the base diameter to meet the body, and, the overall length (with or without truncating it at the very end for the entranceway) which will give Pierre the correct single piece shape for attachment to his tunnel. This will maintain tension from the tube to the ground as a single calculation between the two points in simplified form. (Or playing with calculus if you prefer.)

The floor will become a large flat shape, connected as Pierre wishes. Since, erected on a flat surface, the ground will work as a floor, there will be little structural involvement, except for holding the "legs" in position.

Tensioning is certainly possible without a lot of triangular cuts and seams. Vents, doors, and vestibules can all be added as needed. But these are more complex, and adds more seams, but can be ignored.

This is all in an ideal world. In use, we all know things don't work this cleanly. A slight shift beween the orientation of the legs will indeed change the overall tension. I agree with Roger in this regard. But it doesn't matter what initial shape the ends meet the body, it just increases the amount of waste material. Tensioning becomes more asymetric, but still possible such as the difference between Rogers "gambrell" designs or Expeds semi-circular designs. Ideal pitches are rare on camp sites. It will always show some unevenness on a rigid structure which will always transfer to the canopy with a tunnel design.

[Pierre Descoteaux]

Oliver, nope, I did not cut into my cuben yet. I'm trying to slowly finish a 4th backpack. This keeps me busy enough that I don't feel the rush to jump into the tent construction. Plus, I need 2 more paycheck in order to by my carbon fiber pole/probes, silnylon, and many other needed things for the project.

I still need to figure out how to design my ends so that I can use math to have an idea of the surfaces involved. The curvature of the pole simply does not make the base of a cone… The cylindrical part is much simpler like James M said.

I'm not, at this stage willing to scrap my idea to build a mid but I thank you for voicing all your concerns. Your links where also helpful. I will at some point build an ''MSR Twin Sister'' but not this time around.

I'm thinking that if it all fails I'll still have tons of cuben laminate to build stuff in order to drown my sorrow… And a lifetime of we told you so…

But again, my not so conical ends needs some work. I did make them 5cm longer like RC suggested in an email and I am redrawing the whole tent with more details/accuracy. Once I have my poles, I'll build a mockup for the ends just to make sure it all work since my brain can't handle those calculations…

Thanks to all!

[Roger Caffin]

Hi Pierre

> The curvature of the pole simply does not make the base of a cone…
Why not?

OK, so when you bend the pole it will look like a parabola, not a semi-circle. But that does not mean the poles will be in a parabola when used in the field. Add some guy ropes at the sides and the curves will be … well, maybe 'odd'?

Ignore all that, assume the poles make semi-circles, and make the patterns that way. Then tension the guy ropes so the fabric looks right – no wrinkles. Works for me.

Cheers

[James Marco]

Yeah, I agree with Roger. You cannot design for all the variences of the ground, nor variences in pole archtecture. A slight bend will shift things around. You are pretty much stuck designing for the ideal shape (semi-circular) as the best average shape you will have, then fudging things to make them work in use…as Roger does with the guy lines and side skirts he uses. This stuff may leave some wrinkles in the canopy, especially with cuben, but will still work fine.

There are several conic design programs out there. For a tent, they get awkward because the size is nowhere near the actual size of a tent. Just be prepared to have some scrap material. I think I would design similar ends, then cut in a door and vents after the pieces have been fitted, adding rain flaps as needed and/or making new pieces for those that don't work. Mostly the door will be over the vestibule and even if you get a minor leak it will not be the tent body, and the rear will need a smaller vent, anyway. You can add a front vent over the door or incorporate it into the door, both work. Inside, you need only a mesh door.

It sounds like "cobbling", and to an extent, it is. But if it works, so what? It isn't like you will be making a hundred of them with CNC cutters and need to get the calculations perfect. It will keep things light and still work well.

[Sam Farrington]

Pierre,
When you get around to cutting up the Cuben, PM me if you'd like some free sub one oz sail cloth that is non-elastic. If you can't make a mock-up of a tunnel tent that is taut with the sail cloth, you probably won't do much better with the expensive Cuben. Of course, that doesn't resolve the seam strength issues, but it would take you another step in deciding whether a tunnel is feasible, or a mid is much more the way to go.

If you do send a PM, please remember to include an email address in the PM, as I can receive PM's, but can't reply due to some glitches that were not resolved.

Some years back, when sail cloth was all the rage, I ordered several varieties from KiteBuilder and other sites. I'd be glad to get rid of it if someone can use it.

[Paul McLaughlin]

If I were trying to proto a cuben tent I'd do it in heavy paper. It is not going to stretch and will be mercilessly unforgiving in terms of uneven stresses. If you can make a paper prototype the will hold together, then I'd expect it to work great in cuben.
In the construction world we use heavy paper for protecting newly installed surfaces like hardwood floors and countertops, so you can get red rosin paper (actual color is sort of a muted pink) in a big roll for about 10-12 bucks – that's 36" wide by about 160 feet. So it's cheap. Tape it together and have a go.

[Colin Krusor]

I second Paul's recommendation. Butcher paper and Tyvek have worked well for me for making patterns for cuben shelters. As Paul wrote, paper has zero stretch, so fiddling with the paper model will really help to get rid of wrinkles at the design stage. Just be sure to use thin paper or Tyvek that doesn't have much rigidity. If it's thicker and has some stiffness, it will form nice tidy corners where the cuben might crinkle and sag.

[Pierre Descoteaux]

Hello all,
Here is a short update on the progress of this project.
The main fly is complete withe the 4 pole sleeves. Some parts of the inner are cut as is the bath tub floor pieces. And I still need to make the two ends. I'll play with all of that during Xmas and beyond.

I hope these pics all work…
Cheers.

[Jesus Cardenas]

I am so interested in seeing how is this going to turn out

[Sam Farrington]

WOW for sure. If that's the Cuben, please tell us more about how you decided to join the pieces. Thanks.

[Pierre Descoteaux]

A short update… The cone ends are now in place. The meeting edges of the fly and the ends were both rolled twice and taped with the double sided tape from Cubic tech. Then, I used the same tape to bond the two edges together. I also went with two parallel rows of stitches. I of corse used Rasant 75 for the sewing… The gap between the fly and the ground is smaller then expected so I will wait before adding a sod cloth. I also had to change my pole cup holders. Using cuben hybrid seemed like a good idea but it slipped too often off the pole end. I'm now using the protective caps that come with ice screws. It's a flexible and durable material. So far so good.
I'm now testing contact cement to make the for tie outs that will hold the ends in place at ground level. Hysol U-09FL is simply too hard to get here in Canada… Plus I had a can… Again, so far so good. A test tie out is holding 46lbs without any issues for now. It is bonded with Lepage Contact Cement and three short rows of stitches. I tried to replicate the corner reinforcement from the sail makers… It goes like this, bond a big circle of ct2k folded over the edge of the fly. Add a smaller circle using the same technique. Than bonded and sewed on top if it all ( 3rows of stitches) a 2" by 4" strip of cuben that was folded and bonded twice lenght wise. Also the bottom edges of the fly are all rolled twice and bonded with the cubic thech double sided tape.
Hope this all make sense.
Some pics…
And a huge Merci! To Sam F for some material help. It made everything easier on my nerves…

[Sam Farrington]

Pierre,
Thank you much for the update. Hope you will post about zippers and entrances at some point. Several years ago there was a post about the company Fastenal's website sales of the Hysol low viscosity urethane glue, and I ordered from them with no problem. They are a large company and possibly might ship to Canada.

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