Modified A-Frame tarp, fully enclosed

[Kai Harris]

I've wanted to try building a shelter for awhile. MYOG experience to date is a synthetic quilt that I had a great time sewing. Tossed around different ideas but the goal of how efficiently fabric could be used piqued my curiosity and interest and I've been playing with variations on Aaron Sorenson's 4 yard shelter using Cuben, moving more and more towards making a fully enclosed shelter. With SilNylon, there's an additional 5" of fabric width that allows quite a bit of additional flexibility. And since I'm using Sil, fabric efficiency is more a function of neat design than cost so I didn't sweat adding fabric to meet design goals as long as I could use it efficiently. I ended up switching to 4 linear meters instead of yards (ordering from ExtremTextil) fairly early on, which gives an additional foot of fabric. And then as I switched to an overlapping flap closure, I needed to add another foot of fabric. This shelter could be built in 4 meters (4.37 yards) of fabric using a zipper closure rather than overlapping flap closure. The design below uses 4.7 linear yards.

Before I actually build this thing I want to share it, get feedback, and see if I'm making any collossal newbie mistakes.

Design goals:
* full-height entry – no ducking/crawling under a beak
* full coverage, I'm not super confident in my ability to set up the shelter so that weather hits it from the "right" direction
* efficient fabric usage, minimal waste
* tall enough to sit up in & wide enough for good coverage
* simplish design, doable for my skillset

I ended up using a slightly modified body from Aaron's 4 yard design and then added a half-mid to the front instead of the beak to give it full coverage. Like Aaron's, the apex is supported with inverted V trekking poles. The door moves to the side. It would generally be pitched 3-5 inches off the ground to improve ventilation. The middle of the foot could be lifted a couple of inches with a guy line and a stick to help ventilation as well. Halfway down the back of the body towards the foot has a guy-out point to help lift the body and keep it tensioned.

The tarp uses an overlapping flap closure instead of a zipper – saw this referenced on BPL and then spent a long time looking at ZPacks photos. It has 16" of overlap at the top, tapering to none at the bottom. So half-way down (below where sleeping area ends), it has 8" overlap. Really like the simplicity and not having to sew in a zipper. I am concerned with it leaking as part of it is over the sleeping area. Will probably try it with the overlap and can add a zipper later if necessary.

I plan on using 6-8" loops of shockcord tied to each of the guy out points to help with sag from moisture. Guy out points are on every corner (except where the trekking poles attach), the middle of the foot, the middle main body sides, and halfway down the back of the body to lift.

Questions / feedback:
* Thoughts/experience with overlapping flap for door closure instead of zipper – is this a terrible idea?
** The foot end will point into the weather, so this flap would be on top of the head side flap
* Confirming I can use either side of the SilNylon as the "up" side
* Strategies for mitigating sag/stretch – especially a concern with flap door closure
** 6-8" of shockcord tied into ~2.5-3.5" loop at each guy out point
* Tie-out attachment points made from scrap Sil should be strong enough or should I use grosgrain?

Dimensions
120" long, 84" body & 36" head. 52" wide, tapering to 32" at foot. 42" tall.

Here are the pictures – 1 square of graph paper = 4 inches.

Next step is probably mocking it up with painters tarps. I'll update this thread as the build progresses.

Estimated weight ~12.5 oz
8.5 oz – 4.7 linear yards of fabric, design is not 100% efficient so actual weight will be a bit less
1.5 oz – 3 8" Easton stakes
0.9 oz – 3 6" ti stakes
0.5 oz – 7 6" sections of shockcord (3/16 shockcord .13 oz/ft)
0.5 oz – 5 12" guy lines & 1 6' guy line for lifter & middle of foot (NiteIze reflective)
0.6 oz – 6 guyline adjusters (might not need these or the 12" guy lines with the shockcord)

[jimmer ultralight]

IMHO, you need to rethink the flat on the backside.

Great place for water/snow to collect on such a gradual slope. Not good;)

Look at what Henry Shires did to the Contrail design to create the Protrail.
Thats your clue.

Otherwise,it looks great.

[James Marco]

Yes. The flat rear panel poses a problem and there is no ventilation.

1) The flat panel will have rather poor run-off/snow resistance as Jimmer said.
2) The flat panel also cuts down on internal height. I have a similar MYOG tarp that I use a 12" found stick as a rear pole. Basically, this adds 12" to the internal height by narrowing the rear a bit, but I start out with about 64" (built for two.)
3) Designing in ventilation will save some material. A peak vent would be nice (no savings there) and some front/rear flow-through opening.

I simply opted for beaks at the front. This also sets up for an entrance. Careful design will give you similar angles between the front to back and side to side pitch on the beak. This will let you push up the beak about 12" without disrupting the staking for the tarp even though it is a solidly sewn piece…no zippers. It also supplies good ventilation and good rain resistance, in the 10' length you mention, along with the 12" rear opening.

Similar to this:

[Jerry Adams]

I've done similiar tarps – too small inside

Pyramid works better – tall enough to sit up on sleeping bag with plenty of head room, steep walls, open door when not windy/raining for good ventilation.

[Ben Wortman]

Agreed with Jerry
A pyramid of whatever size is also much easier to make that any sort of shaped shelter. I always try to reinvent the wheel on MYOG shelters, but in the end it is very hard to make something better than a simple pyramid of whatever size you like.

Ben

[todd]

Nice design, but I agree with the above about the flat panel issues.

Change that and you have a MLD Patrol / Golite Hut/SL1, GG Spinnshelter type of setup that is proven and sweet!

[Kai Harris]

Thanks, I appreciate the replies and insights.

I really like the side entrance rather than a front entrance like the ProTrail or the various A-frame designs with a beak – and to Jerry's point, it also allows rolling up one or both sides for increased ventilation.

Any thoughts on the overlapping flap closure? It's the close-ups at the bottom of the graph paper model pictures. 16" of overlap at the top tapering to none at the bottom.

Flat slope on the main body – I can see how that could collect water & wind if it isn't steep enough or doesn't have an A pitch. There are guy-out points – you can barely see in the SketchUp image halfway down the flat panel and down at the foot. With a stick and guy-outs I should be able to give the foot a 4-6" A pitch and still have a 30" width. The point half-way down also lets me continue that modified A pitch up the body and pulls the panel out. Is that enough or does it really need to be a straight A pitch?

An alternative would be increasing the 'head' area to 4' and reducing the 'body' area to 6' for more of a pyramid shape. That increases the angle from 26.6 degrees to 30.3 degrees and would still be able to do a slight A pitch with the guy-outs. Mids have those flat panels too but they also have steeper walls – it looks like the commercial manufacturers have a minimum of 42 degrees.
SMD Deschutes: 42.5
MLD SoloMid: 42.2

Hmmm. I hear you on the 'use a proven design' point. Actually thought I was doing that by combining Aaron's with a Mid front.

A 10' x 5' x 48" mid has flat panels with 38.7 degree angle. Much bigger footprint though and you lose those nice steep walls around the head area in mine.

[Roger Caffin]

> I really like the side entrance rather than a front entrance
Until you try to get in or out of the tent while it is raining heavily. Then you find out why it is such a bad idea.

Cheers

[Kai Harris]

Pondering the feedback I've received and reflecting on how I came to the design that I ended up posting here – looking back as I look forward. Realizing also that the tarp isn't so much a modified A-Frame as it is an asymmetrical Mid where the apex is closer to the head than the foot. I also reread Jerry's mid article yesterday evening while planning a path forward. This post is mostly a summary of my processing.

Design influences (not that what I came up with looks anything like these, just that I remember thinking about them and looking at their features)
* aforementioned design from Aaron
* flat tarp pitches, especially in A frame storm mode where the foot is staked to the ground
* SMD Deschutes & Gatewood cape
* lots of shaped A frame builds
* MLD grace and patrol shelter
* ZPacks overlapping flap closure
* TarpTents – I have a SS2 and really appreciate the steep walls

I also caught up in using the fabric as efficiently as possible. Funny how I neglected to realize that mids are wonderfully efficient. In any case, of course a good shelter is more important than efficient fabric usage.

concerns raised
1). small size. I *think* it would be large enough. I'm 5' 9" and fit well into the guyed out version in my yard. It's wider & longer than a solomid or deschutes, but is 6" shorter than the solomid when pitched to the ground. Not planning on pitching to the ground though so my pitched height will be close to solomid and I can sit up on top of my pad even when it is pitched to ground. There is less usable space at the foot because of the shallower angle of the panel but it's longer and there is more usable space at the head with steeper angles. Wind deflection at the foot is a concern discussed in next concern.

2). flat panel – wind & rain. The death knell for the design. The flat panel is substantially longer than the flat panels on cottage mids. And it is pitched at a shallower angle. From my second post, if I switch to 72" body and 48" head then the panel angle increases to 30.3 degrees. A Deschutes tarp has the shallowest angle I can find at 37.3 degrees (I miscalculated it in my post above). But its horizontal length is 52.5" vs 72" in mine so ~2/3 the panel size with a steeper angle. Reducing total length to 9' with a 60" body and 48" head has a 35 degree angle on the body side. But at this point it's so close to a symmetrical mid why not just do that.

Are there any examples of asymmetrical mids where the apex is closer to the head than the foot? I suspect you all helped me discovered why there aren't any?

If I do end up doing a mid, I'll probably do a solomid clone, perhaps a bit wider.

3). Side entry – rain during ingress and egress. This is a concern. And it would be a concern with any solo sized mid, right? A feature that favors the a frame designs for sure.

Thanks for the thoughts & any additional comments – I need to decide now if I want to do a mid or an A frame ala ProTrail, patrol shelter, et al. In any case, I'll be offline for a couple days, look forward to picking this back up when I'm back!

[todd]

I, too, prefer side entry so I don't have to crawl (my knees especially don't like it).

Roger is correct about hard rain being a detriment with this design, but I have found a few precautions really help in this regard:

– Unless it's a clear evening, I push my gear away from the door side so when I open it, gear isn't much affected by the rain
– a square of packtowel helps with any splash/splatter that finds its way in
– This is a no-brainer, but when it rains, move quickly!

I haven't used the overlapping doors, but with decent closures you should be fine.

[Jerry Adams]

I've been using this:

Kind of a mid with one half turned into a triangle beak. I haven't seen anyone sell something like this. Someone has something similar with the beak totally removed, but it seems like that won't be so wind proof.

[IVO K]

"I haven't seen anyone sell something like this."

@ Jerry:

Perhaps no one does, but the Zpacks' Hexamid Solo with the stormdoors comes awfully close.
I have one (MYOG from a Hex Solo tarp and overlapping doors before ZPacks started offering this configuration), and it has served me quite well since Spring '2014.
Very similar footprint to what you show here, great functionality, and Caffin's concern of things getting wet inside during wet ingress/egress is fully and adequately addressed.

The only drawbacks I have to deal with are the low-sloping walls above my face, which is chiefly a psychological issue, and the limited "gear" space in the half of the vestibule which I choose to designate as the "non-entry" half. I can not spread out my kitchen stuff, water vessels, my (wet) shoes, my (wet) pack, and dripping wet raingear adequately, and have learned to accept the inherent limitations. Besides getting quite skilled at peeing in my cookpot to reduce the need of having to leave the tarp….
I strongly suspect that only a Duomid's or Khufu's "half-vestibule" would properly address this, and am stubbornly unwilling to pay the price – neither in money nor in weight.

[Franco Darioli]

The Oware Alphamid is that type of shelter without the beak.
The SMD Gatewood Cape can be set up like that , half a mid with a beak but a small pull out on the long non beak side.

[Jerry Adams]

yeah, hexamid solo is pretty close, but it also has a floor and netting which can be a good or bad thing

oware alphamid has a flat side which isn't as windproof?

if the hexamid solo or my version doesn't have enough sheltered space, then a regular pyramid is good

I sometimes cook in mine. The entry area is good for wet gear, after I zip down the door.

[Ross L]

Kai
Your design looks an awful lot like the old Integral Designs Sil Shelter which I used extensively from 1999-2011. I did not like the front entry, the overlapping door closure, or the long unsupported fabric behind the pole. I now use a cuben duomid and would never go back to a shelter of this design. (on the plus side it was pretty bomber except in a snowstorm and mine only weighed 13.5 oz)

[IVO K]

"…hexamid solo is pretty close, but it also has a floor and netting"

No floor, nor netting. I was discussing the Hexamid Solo tarp, not the tent.

Never mind…

[Jerry Adams]

ahhh… I just quickly glanced at their site

to me, that's a pretty good design for solo. Regular mid for two people if you don't mind the pole between you.

[Kai Harris]

Thanks all for the input! I'm going to build something like Jerry's mid with a beak and the ZPacks Hexamid designs.

One fabric question – I purchased some 20D silnylon from ExtremTextil just before Richard Nisley posted his HH tests of the material. I'm disappointed with the 773mm HH result that Richard found after aging the fabric. Is the real-world impact of this just that it will mist more?

[Jerry Adams]

I've made a number of tents from cheap 2nds sill which is worse. Sure, maybe it "mists" a little but it's never bothered me. In a heavy rain, I'll feel a little, but I don't notice anything getting wet.

There's also humidity and splash. And there's condensation on the inside that can be knocked onto my gear. Your gear tends to get a little damp sometimes. My sleeping bag dries out a little from body heat which more than makes up for any mist.

But, I'd get the better HH fabric if possible. But if I already had it, I'd just use it.

You might decide to make another one at some point anyway.

[Aaron Sorensen]

Gotta say I like James idea a lot.

If I was going to make something with 61" of usable width for 2 people, it would be off James drawing.
You could even have it fully inclosed like you would want.

The only difference I would do is get pole extenders for a 60" length so the width can easily accommodate 2.
I would raise the V in the back to about 24" to give you more ventilation and to be able to cut the length off some as it would have enough hight for the feet.

The one big thing about making a modified A-Frame vs the way you are thinking about going is the footprint size.
An A-Frame can take up much less of a footprint vs the area you need for all the tie outs on the other.

[Author]

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