Input on MYOG tarp/tent design?

The one thing that I found to be an unexpected challenge was the layout of the fabric for cutting. Shelter dimensions are larger than anything I had dealt with, so some new tools had to appear. Since I did not have a large cutting table, I found some very large pieces of cardboard, and those became the temporary cutting table.

–B.G.–

Looks like a lot of fun to make. I'm actually planning on making something similar. My tent will be for 2 persons with a design similar to a Nemo meta 2P, but with a separate mesh inner.

I'm going to make mine with a catenary curve at the top ridge. I'm still doubting if I should make CC's for the other seams. Your design has a very small top ridge, so you may not need one there.

If your poles would be standing vertically, you might be able to go without guylines (although I wouldn't recommend it), but with your current design I don't think you can go without them. You could consider making your tent a little wider at the top for extra stability and a little more weight (I'm guessing about 40 gram). It would be even more stable if you let the poles come together at the top to make an A-frame. The tent would be lighter that way, but you'd also have less headroom.

The only thing stopping me from actually making my tent is that I haven't been able to find lightweight silnylon with a decent hydrostatic head. When I go to Norway, England or some other place where I can expect a lot of rain I want something that I can trust to be waterproof. The HH for 1.1 oz silnylon of the suppliers I've been able to verify so far (Extremtextil, Quest Outfitters and Backwood Daydreamer) have all been below 1500 when they're new.

I've been experimenting with Google SketchUp a little bit over the last few days as well, with plans to build a shaped tarp + mini inner tent / bivy. One thing I can say for sure is that your computer design skills are several orders of magnitude more polished than mine.

The design looks good! I actually just got a SMD Wild Oasis a couple months ago, which I've set up but haven't had a chance to use on a trip yet. One thing I read about it in the PCT trail journal articles that were published here on BPL a few months ago is that the mesh skirt acts as an "intake valve" for mice and other critters, who get in easily but can't get out. Although that's not a huge deal, I think I'd prefer a built in bathtub floor on my tent, so I'm either going to make one from scratch or modify my Wild Oasis.

Have you considered adding in a built in floor? I'm not sure if this is important to you. Maybe you could try doing it ZPacks Hexamid style and just use the nanoseeum netting for it (but you'd probably need a ground sheet to protect it?)

Another thing that I've read about the SMD Wild Oasis is that the ventilation is a little sketchy (as per BPL review: http://www.backpackinglight.com/cgi-bin/backpackinglight/six_moon_designs_wild_oasis_tent_review.html). It recommends a higher pitch / shorter side walls to increase ventilation. Maybe that's something to take into consideration?

Also, what type of practice fabric/material will you be using? I'd be interested to know since I'll definitely need some sewing practice when I attempt to make my own tent in the next couple of weeks.

Bob, cardboard idea is a good one.

Mark, I staked out hiking poles yesterday to get a sense of the footprint and volume of the shelter, and how the structure will work. See picture below. I think you're right–with such a small ridgeline, cat-cut is unnecessary, esp. if I use a spreader pole. Structure seems pretty stable, even with the angled hiking poles. I'll add points for additional guylines, but hope to get by under most conditions with just grosgrain and ladder-locks at the five stake-out points (green rods in drawings above).

Brenden, your point about the mesh working as a one-way valve for critters is a good one–hadn't thought of that. A zpacks style mesh floor would work (and add ~2.5 oz). Looking at the polycro tube tent design on another thread, I'm wondering about a polycro floor, taped or velcro'd to the perimeter mesh. This could be replaceable, and wouldn't add much weight, since it would take the place of the smaller polycro groundsheet I'd be using anyway.

Re: computer design skills. I just finished a graduate degree in architecture, so have had a little practice. There's a few plugins I've added to SU that make things easier, but mostly getting a decent looking rendering is figuring out how to tweak view settings for best results. This has all the edges turned off, for example, and I've painted most of the surfaces with translucent color to make it easier to see what's going on.

I can get practice fabric free from the local lumber yard. Bunks of lumber come wrapped with a plastic tarp-like fabric, which is usually thrown away. It's heavy (~2.5-3 oz per square yard) and not stretchy like silnylon, but should work fine to test ideas.

The polcryo velcroed to the netting is a good idea, that is what a friend of mine did when making his shelter. Like you said, it doesnt add hardly any weight if you are already bringing the polcryo, so you might as well. It makes sort of a bathtub floor too, so thats an added bonus.

thought about where the front netting will attach to the canopy? If you use the existing front seams, and let the netting fall vertically, it will cut off your floor space at the head end. If you pull it out at the bottom to recover space, at least at the ground level, then there is the issue of how to keep it that way without adding weight. If you are willing to add a canopy seam, or suspend the netting from unreinforced canopy wall, then no problem, but that is not a very elegant solution.

A floor will create some other issues, but you didn't mention a floor, so no comment.

> The polcryo velcroed to the netting is a good idea, that is what a friend of mine did when making his shelter. Like you said, it doesnt add hardly any weight if you are already bringing the polcryo, so you might as well. It makes sort of a bathtub floor too, so thats an added bonus.

John,
How does your friend keep the velcro from ripping up the netting? Velcro is relatively heavy compared to the other materials being used so I take it he uses several very small pieces?

Michael, like you guessed it is just tiny 2×2 or so squares of velcro. It does not have to be very often, just enough to hold the floor up off the ground a little. I dont have his shelter here to look at it, but I would guess that there is probably 5 little squares on each side. Doesnt add up to much.

As for how he keeps it from messing up the netting I am not sure. I think he just glued the square to the netting, and then a matching square on the polycryo.

I was thinking that the netting skirt would just be sewn to the canopy all around the perimeter (except where the door is). That's what I tried to show in the drawings. Basically, the floor space would be the same as the drip line around the canopy. Samuel, I'm having a hard time picturing what you mean by "front" seams.

Regarding comments from others on adding a floor with velcro: I realize now full velcro will be pretty heavy (~2 oz or so–more or less the same as a full mesh floor). Velcro tabs would work, and if the polycro is on top of the mesh, that probably also takes care of the one-way valve problem.

One simple solution I thought of is sewing the polycro to the mesh, then when it's time to replace the floor, cutting away most of the polycro and leaving a 1-2" strip of it still sewn to mesh. The new floor can be attached to the strip with the same double-sided tape that comes with polycro window film.

After testing the size and structure, I think I'm ready to make some patterns from my SketchUp model, then sew a prototype. Hope to get this done over the next couple weeks, and post pictures.

David,
OK, I see it now. Thought they were snowskirts.
Great design. Looks like you will have some kind of arrangement for netting just behind the door so that when it's buggy but not raining, you can leave the door open to reduce condensation. Looking forward to the pix when completed.
Thanks.

> not sure if I need a spreader pole between them (horizontal red rod–little hard to see)

I think you'll need a spreader bar, or guying from the top of the poles. I don't think the geometry of the sidewall tension will provide an adequate lateral force to hold the poles apart otherwise.

I've also been using SketchUp for designing tents, also using two poles. I came up with a different way of keeping them apart, which is to cross them over near the apex, an idea I had six years ago (almost to the day…), but have never got around to implementing… This also gives a very stable structure.

Here's my sketch:

There's a through-flow vent structure at the top, too, backed by midge netting.

There appears to be a lot of wasted space under the fly, but it's intended for cooking and storage; a trade-off between fly weight and inner weight. The width of the inner is largely determined by the maximum separation of the crossed poles.

David,

Here’s an easy way to add a cross pole to two vertical poles.

POLE

I only recently came up with it. Don’t have a lot of experience with it yet.

Daryl

Hi Daryl,
That's exactly what I was thinking–have seen kite frames that use the same sort of connection. When I tested the pole structure in my back yard, I just made a couple tubes w/ duct tape. Seems like a tube sewn out of wide, flat webbing (or the right diameter of tubular webbing) might also work, altho' it wouldn't have the grip the aquarium hose has.

Kevin,
The cross-pole structure is pretty interesting, and a neat way to stabilize the structure. Not sure I want to sacrifice the headroom, however.

Testing my structure, it looks like a spreader is only necessary if the ridge line is in compression, which is dependent on the width between stakes at the foot of the canopy (at least using lines to substitute for fabric–see photo above). But as long as the spreader is pinned to the two poles, it can act in compression and tension, and I like the way a lateral load on one pole is transferred to the other pole with a spreader. Of course, panels of fabric instead of the few guylines I used in my test will create diagonal connections between pole tips and stakes, and should make the structure more rigid.

David,

Here’s another idea for your consideration.

Cork

Daryl

Thanks Daryl. Sure would be great if there was a way to search member profiles for posts in a single forum–I'd like to search all your previous MYOG posts. And I should say, your posts on the tent you've been making have been very helpful.

Based on your experience, would you recommend cat-cuts on all the long seams in my design? Bearing in mind that I'll be using silnylon rather than cuben? (I assume silnylon's ability to stretch a bit will help with a taut pitch, based on experience with the fly on my current tent).

I don't think you need a spreader bar if you are using poles. Take a look at the Big Sky Wisp. That thing works just fine and felt very sturdy. I would still plan for the option of using a spreader bar so that you can hang the shelter instead of using poles.

David,

Here’s a link to a discussion that Samuel Farrington and I had about cat cuts.

CAT

Daryl

Wther a cross-bar is needed can probably be determined by looking at the geometry of whatever is being used to pull the pole sideways from the centre of the tent. The steeper that is to the vertical, the greater the tension required for a given outward force (the usual problem of resolving triangulated forces into perpendicular components). For a tension, T, in a supporting element at an angle theta from the horzontal, the horizontal component, H, is T.cos(theta), and vertical component T.sin(theta). Re-arranging the horizontal component for a given horizontal force, Hg, we get T=Hg/cos(theta). And the usual problem occurs if theta approaches 90 degrees, where cos(theta) tends to zero, so T tends to infinity (hence does V).

In other words, keep the angled side support at a shallow angle…

Whether the sidewall support is merely the angled sidewall (providing a force over the entire area of the sidewall, but, ultimately, converging on the pegging points), or a guyline are the options.

With a single pole, the tension in the two sides stops the pole moving. If only one side is supported, the system is less stable.

Obviously, the horizontal load to be supported is that of wind loading…

Experiment will give us the answer though.

> Not sure I want to sacrifice the headroom, however.

Yup, that's certainly an issue, and depends on where you cross the poles (and thus the width of the apex of the tent). The limit case is no crossover, and the poles resting against each other, which is the classic A-frame.

Posted rather hastily, I'm afraid, so apologies if my thoughts are garbled or seem abrupt.

Kevin,

I like your X shaped cross bar idea. I'm typically interested in a double wall tent (fly + inner tent) and the X shaped cross bar does a good job of separating the two at the top of the tent.

The cross bar would give the fly a truncated top and I'd use a single pointed top for the tent.

Looking forward to fooling around with the idea.

Daryl

just assumed you were going to use a spreader bar.

The threads about the Lightheart Gear tents talk about instability being a problem at the points where the spreader bar connects to the hiking poles.

You could spend a lot of time on this issue, as it goes all the way back to the early tents made by the company that preceded Eureka! – have forgotten the name.

The Dana Designs Javelina and a number of others have come up with inventive ways to connect the spreader bar to the poles.

If done correctly, the poles will put tension on the bar, bending it slightly convex (upward), thus adding rigidity to the assembled wicket.

Sorry I don't have any great ideas for you about this. Maybe others will share some on this thread.

> Wther a cross-bar is needed can probably be determined by looking at the geometry

I said I was rushed…

When I said ‘cross-bar’, I meant ‘spreader bar’, ie. a bar between the two poles to hold the poles apart.

The crossed poles allow the structure to have the rigidity of a triangle, whilst giving a shape that isn’t triangular. IYSWIM…

My comment about using guylines to hold the poles is demonstrated in Daryl’s Cork photos, where shallow guylines hold the tent in shape.

Another example of this type of tent is the Mountain Equipment AR Ultralite. It uses no spreader bar, but does have guys at the side.

Kevin,

I checked out the link you posted about the Mountain Equipment Tent.

That is a pretty light tent at about 3 lbs 2 ounces for tent, fly and poles. I also like that it doesn't have very much mosquito netting.

I notice that tents made in the UK often have less mosquito netting than most US tents. I like that because the weather here in Seattle is more like that of the UK.

I saw a tent very much like the Mountain Equipment Tent in the early 70s in a store front window in Victoria or Vancouver British Columbia. I liked the side entry so much that I started fiddling with myog tents and have been doing so ever since.

Daryl

"I was thinking that the netting skirt would just be sewn to the canopy all around the perimeter "

I'd advise against this. Wind will blow rain water running off the wall into the mesh, which will then wick the water onto your floor.

Silicone the mesh onto the canopy a few inches inboard of the hem edge.

Finished tarptent prototype in test material today. Here's some pics:

Sewed this out of recycled lumber wrap. Pitched pretty solid, but need cat cuts on most seams for tautness, I think.

Space inside is pretty generous for one. Clothes pins on seams are testing how deep cat cuts should be (got that idea from one of Daryl Clark's projects).

Spreader bar was needed. Bar is 13.5" long, and tensioned with a ladder lock. Hiking pole tips are set into grommets. Will need to sew a pocket in canopy above pole tips so they don't press against fabric.

Head end of tent, tensioned with single stake. I sewed seams facing out so that resewing into a cat curve would be easy. Also, would do it this way for flat felled seams in actual tent.

Didn't realize I could get away with rolling up the whole front. Only four stakes holding this, and it's still pretty solid. Room for two, if they're willing to be snug. Widening the center panels by 6-8" inches would make a good 2 person shelter, I think.

My kids, testing things out.

I figured out a lot doing this–well worth the few hours to sew a test version. I want to sew the cat curves into it in a day or two and re-pitch.

I'm thinking now I won't attach any mesh to the canopy, and make either a mesh inner tent or bivy or both, for a modular set up. Final version in silnylon (with zipper, etc) should be around 10-13 oz. Hope to start it in a week or so.

Thanks for all the comments and suggestions so far–welcome any more input you have.