Dec 3, 2013 at 12:44 am #1310522
I was thinking about sewing an 8 sided tipi for winter snowshoeing.
Probably a total length of ~9.5ft and height of ~6.25ft tall.
This would make each of the 8 side panels aproximately 4ft by 8ft.
The theoretical total weight of fabric would be around 19oz… who knows how much it would weigh with all the trappings. I would guess 25oz with peak reinforcement, webbing for tie outs, and seam sealing.
My justification for 8 sided is better wind resistance than a pyramid and I think it will take snowloading better.
When I look at pictures of megalights, supermids, ultramids, etc… it seems like the fabric collapses in between the mid edge stake and the corners causing more snow to accumulate. I figure I will get a little bit less of this effect with 8 sides. Now, I realize that I will still get some of the same effect but I think it should be lessened due to being able to tension all the stake properly instead of worrying about staking out the midpanels too tight. I also figure I can put more tension on all 8 stakes and will get a stronger pitch.
I like the idea of 8 sides over the 6 sided shangri-la approach since I think the shangri-la isn't as idiot proof. I find it difficult to balance the staking tension and location. With the octagon I ca stake a square, tension, stake the second square, and then tension.
Anyone think of a reason not to do it…. besided the fact that it will suck to sew 71ft of felled seams?
(Please excuse my tablet related spelling errors, feel free to harrass me about mixing up "seems" and "seams")Dec 3, 2013 at 6:46 am #2050274
71 feet of flat felled seams is no problem. Actually, with 4 sides, there's typically a seam down the middle of each panel so the length of flat felled seam is the same.
Who is it that makes a similar 8 sided pyramid, Rota Luca? That should work well.
You may find there isn't that much difference between 8 sided and 4 sided. Have a stake in the middle of each of the 4 sides, and the wind and snow resistance will be about the same. The middle stake will pull out the fabric a little so it's sort of 8 sided.
When you lay out on a roll of fabric, the 4 sided tent may use less fabric. Each of the 4 sides consists of 2 panels. The 2 panels can be right next to each other on the fabric roll, with points going the opposite direction.
Maybe have the fabric going sideways rather than lengthwise. If the fabric is 60 inches wide, have a sideways seam 60 inches up from the bottom going all the way around. Then you'll have less waste, won't need to buy as much fabric.Dec 3, 2013 at 9:16 am #2050319
The plan was to do the horizontal seams. Since am making 4 by 8 foot triangles I would make a trapazoid that was 5 feet tall, with a base of 4 feet and a top of 1.5 feet. Then sew a triangle that is 1.5 foot by 3 feet to the top of that.
MLD style… (sorry Ron, can't afford a supermid)
AnthonyDec 3, 2013 at 10:14 am #2050343
@wsafleyLocale: Eastern NC
Just wondering, wouldn't horizontal seams be more prone to leaking than vertical seams? It would have all of the water collected by the top portion running over it instead of a much smaller portion of runoff for the material above a vertical seam. Maybe it wouldn't matter in practice if the seam is well-sealed?Dec 3, 2013 at 10:21 am #2050345
I don't think it would make a huge difference once seam sealed. MLD does horizontal seams on their bigger mids and everyone is in love with the duomid. If they all leaked I bet people wouldn't like them so much.
But now that you mention it I'll try and make sure to sew the seam such that the faux-felled seams have the fold going down so there is no lip for water to catch on.
AnhonyDec 3, 2013 at 12:46 pm #2050410
@rcaffinLocale: Wollemi & Kosciusko NPs, Europe
> I'll try and make sure to sew the seam such that the faux-felled seams have the fold
> going down so there is no lip for water to catch on.
Put the seam in the inside and seam seal the outside. Clean surface, water will skate right off.
CheersDec 3, 2013 at 1:46 pm #2050430
hmmm… except ignoring the seam sealer (which might fail) then any water flowing down would flow into the seam, and then inside the tent.
with the flat fell on the outside, if you fold it downhill, then (ignoring the seam sealer and the holes the thread goes through) the water would stay on the outside.Dec 3, 2013 at 8:46 pm #2050587
To me one issue would be floor shape and the usability of an octagon versus a square. I think a better approach might be to do a square pyramid, but with some variations from the usual construction. I have an old Chouinard pyramid (predecessor of BD)and the one I have was a warranty replacement for the one I first got, which was in a lighter and VERY stretchy fabric – so stretchy that the pole supplied was too short to get it tight. Both of these have the same issue (of course much worse on the super-stretchy one), which is that when you set it up tight the middle of each side is up off the ground by several inches. This seems mostly to be due to the fact that the corner seams are on the bias while the seams in the middle of the faces are in line with the weave – so the corner seams stretch more. I would reverse this – make the corner seams on the weave and the mid-panel seams on the bias. then when you set up, you pitch the corners tight and any stretch just means you pull the mid-panel stake points a little bit out past a straight line from corner to corner. Thus you can get a tight pitch and have the bottom to the ground all the way around.Dec 3, 2013 at 9:36 pm #2050603
For seams, I would worry about having the fold for a fuax-felled seam on the inside of the tent. If there was any part of the seam where I didn't properly tension the fold the stitching might open up and let water into the seam. I think I'll probably stick to flap on the outside, folded in the downward direction.
The footprint will be a little strange. I figure it won't be too different from a Tigoat Vertex 5, which sleeps two comfortably. Two people was sort of the plan, whether it was me and the girl fiend or a friend. Most times I find it hard to trick more than one other person into winter expeditions with me.
Oh man, I have no clue how I would manage to have the hem cut on a bias without using nearly twice as much fabric. I guess my spacial reasoning isn't good enough. Definitely food for thought. I'll try and figure out a good way to do arrange the material, I suppose do it once the right way.
AnthonyDec 3, 2013 at 10:13 pm #2050613
Hmmm… Interesting idea about having bias go to center.
Layout panels on roll of fabric:
It would take a little extra fabric – length of diagonal is a little bigger. And you'de end up with a long narrow strip of fabric.
You could make side pieces wider than the roll width.Dec 3, 2013 at 10:19 pm #2050614
I can't seem to find a good walk through of making peak vents, anyone have a source?
The way I imagine doing it is to cut a trapazoid out of the top of each of three triangles 6" from the top and sewing netting over the top of the opening then attach a cone of fabric to the edges of the triangle. I'm worried about leaving raw edges and wonder if there is a better way to do it? I'll have to see if I can figure it out off my Shangri-La 3.
I've been doing a bit of reading and it sounds like a couple of people have been saying ditch the vents since they don't do much and affect stability and storm-proofness.
I think I'm keeping them though, I'd feel really uncomfortable cooking in a ventless tent.
Also for the peak reinforcement do you guys think sew the tent in two halves, add the reinforcement then sew both halves together? That was the original plan.Dec 3, 2013 at 10:30 pm #2050619
So this was my initial layout… utilizes all of the fabric which is nice, plus I don't have to make huge mid panel seams.
But Paul had a good point. The hem would be oriented parallel to the ripstop pattern/weave and would therefore stretch less. I would probably get a better pitch with the hem oriented at a 45 degree angle to the weaveDec 3, 2013 at 10:41 pm #2050621
I describe how to do peak reinforcement – http://www.backpackinglight.com/cgi-bin/backpackinglight/myog_silnylon_floorless_2-person_tent.html – towards the bottom
Basically, make tent without reinforcement, set it up (if it's not windy it won't rip without reinforcement), take a circle of fabric for the reinforcement and put it over top. Fold at each of the 8 seams and put a stitch in by hand to make the circle into a cone and have it properly sized to the tent. Take tent down and sew a couple rows of stitches around edge of reinforcement
What I have done more recently is run the zipper all the way to the top so the reinforcement piece covers the top of the zipper – clean look, stronger, more rain resistant.
I think vent is a waste. At least for condensation. I've done it (not very good) and it didn't seem to make any difference. Nowhere near big enough.
If it's still air and cold so you'de get condensation, leave door open. That provides enough ventilation to actually do some good. If it's rainy and/or windy, leave door closed, but then I don't get so much condensation.
You could leave door open to use stove.Dec 3, 2013 at 11:09 pm #2050627
Well, I made a new fabric layout just to see what it would look like
It's more efficient with the material than I was expecting. I might try it out for the sake of strengthening the tent and making it pitch better. I don't think a canti cut is necessary if I do the above
So it looks like I'd use 360" of fabric with the panels oriented diagonally and I'd use 264" for the panels oriented vertically.Dec 3, 2013 at 11:21 pm #2050632
With the fabric laid out diagonally the left over triangle to be added would be ~11" wide by 7" tall. Anyone ever use only the dyneema grid for the peak of a tent instead of under sil-nylon?Dec 4, 2013 at 5:05 am #2050652
Hem on a bias … for the sake of strengthening the tent and making it pitch better.
Um … no? It might help how the pitch looks but it moves the stretch from where you want it (center of panels) to where you don't want it (at the unsupported edges).Dec 4, 2013 at 6:59 am #2050675
Good layout. The edges won't be totally parallel to the grain, but close.
Remember this is an experiment and the finished product may not be useful. Or you'll feel like making a next version based on this prototype. Maybe use cheapest material.
Maybe just cut out one panel and play with it will reveal some problem and then you'll have enough fabric to make it normally.
Don't finish the flat felled seams. Just one row of stitches with raw edges. Finish right at the corners so you can sew on tie-outs. Set up tent. If you don't like it, then make it a catenary curve, and then finish flat felled seam.Dec 4, 2013 at 2:19 pm #2050816
I did the numbers regarding the completed fabric used and square footage
I should use roughly 128(ft^2) of sil-nylon, which is marginally less than the 129.5(ft^2) in the supermid.
My ground area should be 84(ft^2), which again is marginally more than the Supermid's 79(ft^2). Granted my area is a little less usable due to the layout.
My peak height is taller than the Supermid at 6.2ft which I think should shed snow quite nicely.Dec 4, 2013 at 2:25 pm #2050818
Jim if you would be so kind as to expound on your previous thought, I'm not sure I've quite followed you.
Ideally there would be no stretch like in cuben fiber. But I'm working with sil… so I would think that the best way to deal with the stretch would be to orient the least stretchy material along the load bearing seams, the sil should also be stronger along parallel to the weaveDec 4, 2013 at 7:18 pm #2050920
Jim if you would be so kind as to expound on your previous thought, I'm not sure I've quite followed you.
I should start by saying none of these thoughts are originally mine … just things I've picked up following pretty much every BPL MYOG thread over the last 10 years or so.
For structural uses under stress you want two things:
- At seams you want similar stretch characteristics on both sides of the seam. Your idea DOES deliver that except possibly at the seam where you complete the triangle at the top of each panel (I'm not sure of your plans there).
- At the boundaries (the bottom of the tent in your design) you want dimensions to be as stable as possible … stretch is bad there. That was emphatically confirmed in a conversation with BPL's Roger Caffin a year or so ago
Stretch is minimum along the fabric's warp or weft and maximum at a 45 degree angle to those.
edit: stretch inside a panel has advantages in that it is a shock absorber dissipating energy over a longer period of time which reduces the maximum forces the panel experiences.Dec 4, 2013 at 9:51 pm #2050981
Hmmm… I guess if the structural ridge seams stretch you just lengthen you center pole, where you would have to re-stake or tighten your entire perimeter if the hem stretched.
Maybe I'll make one of each and see… sil seconds are cheap
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