myog mountaineering cuben tunnel tent?

[Pierre Descoteaux]

Hello all,
I'm planing to build my own version of a Hilleberg Nammatj 3 / gt hybrid and I've got some questions…
Yes Roger, the tent will have 4 poles with a short span in between but no elbows since the poles will be used as probes (well that is the plan…)
I'm in the testing stages of my external pole sleeves and I was sewing a silnylon pole sleeve to a 1'' wide strip of cuden tape (CT2E-08/PSA has been ordered but I tested with the 3M tape) and then, applying that to my CT2K.18 fly. My testing shows that the cuben/psa strip peels off from the middle (where it is attached/stitched to the silnylon sleeve). Building it like this avoids sewing through the actual fly which I thought was smart. The testing was done by hanging 6Kg to a pole threaded in a 3'' long silnylon sleeve sewed to a 3.5'' long cuben tape stuck to a leftover piece of 1.43ozy cuben wrapped around a wooden piece and held by clamps and some tape. (Jeez, I hope this makes sense. I tried 2 versions and it failed in less than 1hr. I could hear and later see the ''peeling from the middle''. Maybe I was hanging too much weight?

So really, the question is:
How much force can a side wind of 80mph apply to the sleeve? How about wind and snow? From experience, I always end up shoveling as often as needed but still.

Thank you for your time and help.
Pierre

[Stephen M]

Good for you :-)

If it has 4 poles it will be more like a Keron GT Hybrid.

Best of luck.

[Ryan Smith]

Sounds like a cool project. I would probably try heavily reinforcing the area where the cuben fly meets the pole sleeve and then sew like normal.

Ryan

[Paul McLaughlin]

Pierre – a question and a comment:
I'm not totally clear from what you wrote as to whether you are saying the stitching is failing or the adhesion. I think you are saying the adhesion, but re-reading it I'm not certain.
And your testing rig appears as though the cuben that you are bonding the sleeve assembly (by which I mean the assembly consisting of the silnylon sleeve and the connector piece of cuben)to is clamped/wrapped around a wooden slat. I would suggest that this is not a realistic simulation; in the finished tent the fabric would be stretched out from both sides of the connection point, not flat bu much closer to flat than to a directly straight pull as you have it. Whether that will help you I don't know – may make it worse – but it would be more realistic if the fabric stretched away from the attachment point.

And as to how much force your tent would have to really handle in an 80 MPH wind, I did a little googling and came up with some numbers and some really complex answers as well. Leaving the enormous complexities aside, the oversimplified answer is about 15 PSF (note square feet not square inches)at around 80 MPH. If you know the area of your tent you can figure something out from that.

For snow loading, a foot of very wet fresh snow might get up to 25% moisture content, which would translate to about 16 pounds of water per square foot. Of course you mostly have sloping surfaces on a tent so you wouldn't have that pressing directly down on most of it, but it's a lot of weight nonetheless.

[Pierre Descoteaux]

Stephen, the tent will only have one big vestibule. The Keron line up have a long footprint. Simply too long to my taste. But I dig the for poles.

Paul, you had it right the 1st time. The adhesive is failing from the stitching line (the middle of the cuben tape). Even my so so stitching is holding very well. I looked back at all the pictures of my tests and here is one that might give a better idea. Please, disregard the stitching on this picture, that was a bad idea.

Still, I'll see if I have wider leftover pieces to test on a wider surface.
16 PSF. My rig (good or bad) was at 4.4 PSI. (13.2 lbs / 3'' by 1'' cuben strip) which would be 633.6PSF. I might be better of than I was thinking. False hope?
Thank you so very much!!
Pierre

[David Franzen]

I might be wrong but I think paul said your tent will experience 15 pound for everv square foot that your tent is exposed to 80 mph wind. All of this force will then be acting on your sleeves, so that force per area will be much higher there.

[Pierre Descoteaux]

Well, I did some basic math this am and, unless I'm missing something (which would not surprise me…) my technique might still work. Please, bear in mind that I live in a metric world…

Fly surface = 108sqf. 15psf x 108sqf = 1620 pounds (that would assume the wind has the same effect on the whole fly at the same time and not factoring the guy line's effect)
Sleeve adhesive area (for all sleeve added) = 504 sqinches = 3.5sf
1620p / 3,5 = 463psf or 3.2psi.
I'll rig it again with only 10 pounds and using a wider wooden form to ensure a more realistic scenario.

Thank you David and Paul.

[edvin mellergård]

I would put the weights closer to the fabric as well, when the rod flexes more force will be put on the edges than the middle of the bond

[edvin mellergård]

Ok, I have given this some more thought. First of, you got a lot of problem because the load is kind of in peel, not in shear. Search it if you haven't heard about it before.

2nd I also redid the math in metric and corrected a couple of things incase you can figure out away to get the bond in shear and not peel.

Ok, wind force

F = 0.5 * (Air density) * (Wind speed)^2 * (Drag coefficient) * (Area)

Air density at sea level = 1.25 kg/m^3

Wind speed = Lets say a strong storm so 30 m/s

Drag coefficient = Ok, this is tricky, it's the tents shape that determines the drag coefficient and it will be hard to get it exact, but from this study http://www.dtic.mil/get-tr-doc/pdf?AD=AD0701203 page 169 assuming a tent that's 4 times as long as it's wide, twice as wide as high it should be about Cd=0.38

Area, from the side(worst case scenario), lets assume the tens is 4 meters long, 1.2 meters high and got 45 degree ends. A= 4.56 m^2

So the total force from the wind will be F=0.5*1.25*30*30*0.38*4.56 = 974.7 N

________________________________________________

Now, the next problem is that the force from the wind won't spread out even on pole sleeves. If the wind is coming from the side you will have a max force somewhere a little bit above the ground and then decreasing to zero at the top of the tent. The back of the tent will see no force on the bond between the pole sleeves and the fly.

I'm currently away on a long climbing trip and I don't have my engineering handbooks with me so I won't be able to calculate the max force the pole sleeve will feel(it will also depend a lot on the exact geometry of the tent, just like the drag coefficient)

[Pierre Descoteaux]

Wow, thank you Edvin, I knew I needed more brain power!
To be more specific on the tent: 1.8m wide, 1.15m high, 3.35cm long and lets call the ends at a 60deg angle.
Air density will be less since I live at 1050m elevation and tend to go up from there.
Shear vs peel: I'm well aware of the issue hence the testing. I simply can't find a way to attach the pole sleeves to the fly that still minimise the amount of sewing in order not to compromise the mylar and the waterproofness. I'm using heavier cuben (1.0osy) for the fly so I might end up having to sew anyhow. I want external sleeve to ensure that a broken pole wouldn't damage the fly. But I'm open to ideas!
If it gets to that, I can always send you the Sketchup file I have made. Also, my model is not set in stone yet but it is getting close. Plus, I just bought most of my cuben supplies minutes ago.
Enjoy your climbing trip
Pierre
Edited to fix the length. 3.35m not 3.25m

[edvin mellergård]

Hi, 4 tentpoles for a 3.25 meter tunneltent sounds like overkill to me. The Nammatj 3 GT(own one, awesome tent) is 4.05 meters long and got 3 poles. I've been out with it in really heavy snowfall a couple of times aswell as storms and haven't had any problems at all. Are you sure you need that many poles?

If it's to get steeper ends than the Nammatj and Keron tents, have you seen MSR Dragontail where the first and last poles are leaning outwards at the top? It gives the ends a steeper wall but will also make the tent slightly less stormproof.

Anyway, what do you think about using this method to sew the pole sleeves to the fly?

Start by sewing the sleeve to the fly and then bond a piece of cuben to the inside of the fly. Then you get both a reinforcement, waterproofing and worstcase scenario, the threads rip out, the fly will still be in one piece. By folding the sleeve outwards and sew on both sides you'll spread out the load on two seams instead of one if you sew them together. Then just add an extra seam on each side for extra security

You could of course start by reinforcing the fly as well before you start sewing to make it super strong

As for climbing…

Summit of Grand Capucin, Chamonix a few days ago, shouldn't complain :)

[J-L]

I thought that sewing cuben fiber significantly weakened the material?

What is the reasoning behind using silnylon for the pole sleeves? Is it hard to get poles into cuben sleeves? If you are willing to use cuben fiber for the pole sleeves, a fully bonded and double-reinforced sleeve similar to this might work:

Another thought: what about making the poles be internal? Having the poles press outward on the fabric would make things much simpler. Edit: I see, you want them to be external in case the poles break.

[Pierre Descoteaux]

John: I have no experience with this but I thought that the slipperiness and flexibility of the silnylon would make for a better sleeve. Although, I realise that cuben will get significantly more flexible with use.
I'm planing to use CT2K.08/PSA (cuben fiber tape) instead of the CT1K.18/PSA to minimise the sewing issues but it seems obvious that my simplistic taping technique is not enough. The sewing is holding fine but not the bond. I was also hoping to minimise the amount of seams.

Edvin: I'm trying to incorporate most of the good ideas I've seen from all the different designs I have seen and/or used in the past and all the knowledge gained from reading the many posting and articles found on this site. (Roger Caffin, Steven Evans, Lawson Kline, Dan Duston, Steve B, … to name a few). Ideally, I'd use 4 light carbon fiber poles from fliegfix but they have been out of stock for a long while. I may have to go with 2 carbon fibre poles from Fibraplex and 2 DAC aluminium poles. Yes, it does make for a short span between the poles.

Again, thank you for sharing your ideas and opinions.
Cheers
Pierre

[R]

EDIT: Doh! Just noticed John's foot note…

Maybe you're already in progress on a design by now, and maybe I'm missing a key aspect of the tent, but…

Why not put the poles inside the fly? Use a continuous sleeve of the material of your choice, run a single stitch to both close the sleeve and attach it to the fly, and then place a strip of single sided tape on the outside of the fly to both seal the stitch holes and re-enforce the seam. You still get continuous load transfer between the fly and poles, but the load on the sleeve is reduced to stabilizing the pole against horizontal slip, which is a far lesser force as it's perpendicular to wind/snow load.

This won't make any difference to how you pitch the tent.

Furthermore, this can benefit how the inner wall, or tent body, is secured to the fly and poles. I've never handled a Helleberg, but from the catalog photos it looks like the body is attached to the fly at the pole locations w/ a series of short pieces of webbing – these could either be permanently sewn, or secured w/ fastex/side-release buckles. If those pieces of webbing are loops slightly larger in circumference than the effective circumference of your pole sleeve, they can be placed *around* the sleeve *before* it's sewn to the fly. This then securely applies the full tension of the tent body directly to the pole with out any need to re-enforce the sleeve or fly at the attachment points.

As a bonus, this is more aerodynamic than the ridges created by an external sleeve which could make for a quieter night's sleep.

Cheers,
-Rene

[Pierre Descoteaux]

Well, I did some more testing this week and the conclusion for my external pole sleeves is simple: taping only ensures tons of creep until the taped sleeve becomes entirely separated from the fly.
I've now tested 2 other methods that includes sewing and a 3rd one is being tested overnight. So far, it seems that applying a 1'' strip of cuben tape under the fly and then sewing the pole sleeve through both layers ensures a very strong seam and no creep (obviously). I plan to then seal this from the inside with Tuck Tape ''Outdoor repair tape''. I'm hoping to be able to only use 1/2'' cuben tape in order to save a few grams and some money. The CT2K.08 1'' wide tape is pricy.

Question: Should I also seal the seam from the outside?

Again, thanks to all for the ideas!!

[Steven Adeff]

I'm not a big fan of sewing. it requires a thicker cuben so the needle penetrations don't result in tearing, and it compromises the water proof-y-ness of the final product.

While taping has it's downsides, I feel with the proper design the issues can be eliminated.

that said, what I would do is instead of having a long sleeve, I would created multiple loops of cuben (make 1/2" or 1" wide strips by taping in half or 3-fold depending on cuben thickness into long lengths and cutting to length as needed, essentially creating a cuben version of grosgrain).

then use these strips to create loops. that the tube will slide through. placed as often as is necessary for your purpose, and then cover the part taped to the body with a support patch over it.

another option for the design of these loops, where a larger contact area is needed with the body is to cut "dumbell" shaped pieces, with the ends as large as needed to get the required surface area for the strength needed by the taping, then tape as many together as needed before creating your loops. This method does not necessarily require a cover patch either.

[Ryan Smith]

N/M

[Pierre Descoteaux]

I wonder how easily a pole would slide in a sleeve threaded inside such loops… and also if this actually reduces the peeling force and creeping of the adhesive that made me go back to a reinforced fly with stitched sleeve which in my basic testing looked more and more promising.
Thank you for the idea.
Cheers
Pierre

[Roger Caffin]

Hi Pierre

(I was away walking and missed the start of this thread. So this reply is a bit brief.)

Well, several comments. Yes, of course 4 poles are good! :-)

First, bonded junctions are really tricky. But so is using Cuben Fibre fabric. Such junctions work OK when both sides are exactly the same material and the bond is entirely in shear. If any of it is in peel it will fail.

Trying to join non-stretch Cuben and stretchy silnylon is difficult: the load will not be distributed across the lines of sewing the way you want. This usually leads to peel failure.

I have not even tried Cuben sleeves for poles: I think the abrasion factor inside the sleeve would be far too high for safety.

Seam design for poles on a tunnel tent is actually very complex. You need to allow for at least one layer of reinforcing on the surface which is not under tension at all. That is, you need a thin strip of fabric on top of the sleeve to reinforce the sleeve material. I am sure I have posted designs for this previously – somewhere.

Your calculation of wind force giving 1,620 lb force is completely wrong. There is NO WAY any light-weight tent could take that! Edvin's calculation giving ~970 N is much closer to reality. My experience is that if you pitch the tent end-on into the wind, most of the wind will flow over and around the tent anyhow.

Cheers

[Pierre Descoteaux]

hi Roger, I'm glad to get your feedback. And I'm glad to be wrong at this stage of the project.
970N is from the wind only, what about adding some snow loading into the mix?
Also, too many time in the hill, you don't get as much say in how you align the tent. Terrain and ledges are also to be factored in so I'd like to have good faith in the tents ability to handle side winds for those unfortunate times.
I've stared at the drawing of your seam design from another thread for a long hard while. I'm hoping to find a smart way to do it for cuben but so far peel and creep issues are making me believe that I'll have to do some sewing in order to use external pole sleeves which seem to be ideal.

I've placed a strip of 0.51osy cuben tape under the fly (but for the real tent I'll use CT2K.08/PSA which is on it's way). Then, I've sewed (single row of stitches) a double layered silnylon sleeve through both cuben layers and it held 10.6Kg for 24hrs without any issues at all. Even the holes in the mylar had very little stretch. My testing sleeves are short, only 3''. It really feels like this is the way to go. But if I'm wrong, I'd like to know before I start sewing perfectly good cuben!

I could try the same technique with a sleeve made out of some buben hybrid? Or dimension polyant TX07. Could that be better? I bet the flexibility and slipperiness of silnylon will be hard to beat.
Cheers
Pierre

[Roger Caffin]

Hi Pierre

Snow loading: if anything, this would normally add stability to the tent imho. The apparent fly 'weight' would go right up so the tent would not shake nearly as much, and shaking and 'rippling' of the fabric is what will really give you grief, not a steady load. 4 poles should carry a lot of snow load. Spectra or Dacron guy lines are good – visit kite shops for the string.

Tent alignment: yeah, I know, not always perfect. Happens! But often the wind is aligned with the terrain as well, so it is not always a serious problem. Not ALWAYS! Behind a bank of trees is good; behind a large rock can be BAD as the vortices in the wind whip around.

Pole seam design in Cuben: well, not easy. My Cuben testing made the holes stretch, so I gave up, but maybe there's a way. Another part of the reason I gave up was that Cuben does not stretch under load, so it has little energy absorption. That worried me, but the jury is still out on how to handle that problem. Anyhow, I think you may have to cut the Cuben at the pole sleeves, to get the overall shape. I know I have to cut the silnylon there, so I have 3 main roof panels plus the 2 ends sections.

If you are going to go ahead with the Cuben, then I can only suggest lots of load testing first – which we all want to hear about! And some wide bonded cover strips on the inside of the pole seams might do wonders – as some of the diagrams suggest. The bond will be in shear there.

Cheers

[James Marco]

There are a couple considerations that you might have overlooked, Pierre.
1) Balling: In winds with snow, I would get ice balls on the poles where they slipped into the sleeves. (Often, increasing the difficulty in taking a tent down.)
2) Loading for a full sleeve is more even than for loops or partial sleeves. (Especially important in heavy winds.)
3) Loading from the top (snow load) will be of lesser importance with full sleves. The arc on the sides will contribute more to the strength of the roof.
4) Stitching AND taping is recommended for strength. Reference: http://www.backpackinglight.com/cgi-bin/backpackinglight/tunnel_tents_part2_2012.html#.U-yWKqPjRI0
Excerpted:
Internal Storm Guys

In the fourth illustration (near the top) you can see a blue tent pitched on grass in the evening and rather snowed in the next morning. At the very left of the photo you can see the start of a steep bank that was meant to be sheltering the tent. Pitching a tent in a position like this is actually rather dangerous if there is a real storm. The wind came over the barrier in the night and created vortices, which then thumped downwards rather heavily on the top of the tent. Add snow loading on the tent, dumped there because of the barrier slowing the wind down, and you can end up with a very high downwards loading on the top of the tent. The problem with all this is that most tents are designed for a sideways wind – look at the guy ropes for instance. Most tents have a lot of problems with a vertical loading: the middle of the poles or the top of the tent fabric collapses downwards. The results can be unsatisfactory, to say the least.

Tunnel Tents Tutorial and State of the Market Report – Part 2: Tunnel Tents Details and Commercial Models – 15
This problem is shared by all sorts of tents, but unlike many other designs, tunnels do have a way of handling it. We use 'internal storm guys.' Looking at the diagram on the left, we have the wind and snow pressing down on the tent, with a pole shown as a black profile. The inner tent is shown as a green profile. The loading is represented by the red arrows. The result of pressing down on the top of the pole is that it is made to bulge outwards at the sides, as indicated by the blue arrows. Pity the external guy ropes can only provide an outwards pull here. If this bulge goes too far, the poles can (will) snap around about the blue arrows. (Yes, once again, 'trust me, I know.' Oops.)

[Pierre Descoteaux]

Alright Roger, I'll test a short section that would mimic 2 fly panels that would meet vertically (glued and sewed) together with a silnylon sleeve on the outside of that sandwich and taped underneath with 1.75 inches wide tape. It might look like an upside down view of your technique. Flat on the inside with the seam and the sleeve towards the outside. This would be much more complex than my simplistic approach but if it work better, I won't complain.

James, full length sleeves with a closed end is the only way I would envision making my tunnel tent. Internal guys are also planned.They should be easy enough to place on the vestibule pole and on the pole where the inner begins but I'm not sure how to do them for the 2 other poles (i.e. from the pole through the inner fabric?)

Cheer

[Pierre Descoteaux]

Here' s what I meant… I'll let it sit for 24hrs and test.

[Ivo Vanmontfort]

Maybe using a strong cuben (curved) strip with clips.
Ones i made a soulo copy.
neg:
havier?
and clamping the last clip
seems not easy with a non-elastic outer.

[Author]

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