Creating own tarp w/ isosceles triangle calculator

<5oz tarp.

– .51 Cuben fiber.
– Cat cuts.
– No Grommets, no Drings on ridgeline, just tieouts big enough to get thin guy line through.
– No linelocs
– 1-1.25mm guy lines.

Hi Bryce,
You could do the math and calculate angles, or you could use more direct and intuitive methods.

I use SketchUp a lot, plus a plugin that flattens the 3D model into a pattern. SU also calculates area (and volume), making it easy to figure out footprint space and get a pretty good idea of finished weight.

For these tarps:

I just used pieces of paper cut to 1"=1' scale, and played around until I got something I liked. The design came from a discuss on these forums, and basically follows Jerry Adam's suggestion:

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=49480&skip_to_post=432112#432112

I've also staked out poles with string to get an idea what footprint and head room will be like, and made full-scale mockups with lumber wrap (free from the lumber yard). Some of the lumber wrap I've found has some stretch to it (good for modeling silnylon); other kinds don't stretch much at all, which I expect would be good to see how Cuben would behave.

The tarps in the pic above came in between 8.5 and 9 oz (without guylines etc) in 1.1 oz sil with a finished weight ~1.5 oz. They meet all your criteria, and would obviously weigh significantly less in Cuben–I'd guess easily under 5 oz. I pitch with two hiking poles in inverted "V", which provides plenty of room and is very solid, but have tie-outs for pole-less pitches between trees, etc. Will probably add a zipper to the front beak at some point, as it's a bit of a crawl to get in when the tarp is pitched close to the ground.

Here's another pic, from a different trip:

Apologies if this duplicates stuff you already know or have thought of. I'll check out the calculator you found as well.

Hey Bryce,

I don't like most bivys as well, but what about some of the ultralite bivys? Much more comfortable, lighter and breathable. They don't restrict motion, unless you stake them down too tight. I usually don't stake mine down at all.

You should try my SMD Meteor some time. Open, airy, bug-proof. It only gives partial protection, but that protection allows for a smaller tarp and more open/comfortable pitch in the rain.

Also, you can usually just use it as a ground cloth and only crawl in for bug or rain spray protection as needed.

If the rain should turn horizontal, I crawl in and re-situate my orientation so that only the bottom of the bivy gets spray on it. I never know I'm in it when I sleep, but my bag is dry in the morning.

If the forecast is good, I'll pitch my tarp high or don't bother pitching it at all. The bivy helps keep the morning dew off the bag and helps add warmth by reducing drafts.

Our buddy Derek just changed his mind about bivys last weekend when he camped under a tarp inside a Bear Paw Minimalist during an all night hard rain storm.

It kept the bugs off when he went to bed and significantly kept the rain splash off later.
We were forced to camp on hard packed sand that cause splashes to travel several feet, but he was dry in the morning.

David,

those are some sweet looking tarps! Its hard to tell from the pictures but it looks to me like the beak is all one piece, ie. not a separate piece sewn on, the only seam i see is the ridgeline. Is this right? Any chance you would be willing to share a pattern image for that?

those tarps in CF would definitely meet your standards Bryce and be really bomber!

Also check out Laufbursche, i remember seeing a similar styled tarp he custom made from someone, although I cant remember who as of right now.

Thanks Tyler. Again, the design idea is really Jerry Adams’. You’re right–only two pieces total, with main ridge, beak ridge and beak edges cat-cut. For non-stretchy fabrics, I suspect doing cat-cut for all edges would help taut pitch.

Basically, the info for developing a pattern is in the thread I linked to above. This will get you to the top of the thread. I could make a quick drawing of my variation and either email you a .pdf or post here if the OP is interested. The two tarps are slightly different–the one on the right has a longer beak. I made some little paper models, then full-size kraft paper patterns, using a beaded chain and spray paint to lay out the catenary curves.

@Dave — nice looking tarps. Thank you for the tip about Sketch Up.

David,

It might just be me (smartphones are finicky sometimes) but I can't get those links to work :/

Bryce,

Id say best options are: larger tarp like a cubictwin, smaller beaked tarp like the one above, or a hexamid

I used a hexamid twin on the CT is summer (custom .75 in DarthVader black :D ) and my friend used the solo and its a stellar tent. With the extended beak you have full enclosure for even the worst storms

Bryce,

Check out SMD’s Night Wing instructions. It’s cat cut, has a height of 40″ tapering down to 30″ and may be just what you’re looking for if you leave off the mesh skirting and maybe the tail end beak.

This is what I went up going with:
http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=54666

Thanks for everyone suggestions!

David, nice looking tarp!

Here's my version of David's tarp:

David's look a little better : )

My two front poles are Easton Poles in sleeves. I think this makes it hold up a little better in wind. 60 inches long, 50 inch peak, maybe 45 inches of usable head room because peak is so steep.

8 feet long, 60 inches wide at head, 48 inches wide at foot

The sides are on the ground which makes it hold up better in wind. The head end is raised off the ground for ventilation.

One night it was maybe 30 MPH and quite a bit of rain. It held up okay, but rain blew under the raised head end and got on my stuff, but I moved a few things and nothing got significantly wet. Next time I'll have the head end on the ground also.

At the head end the walls are steep, at the foot end the walls not so steep, the two pieces of fabric I used are straight (actually 2 inches of cat curve), I think there should be some sort of curve to make it taut. This might be a case where Sketchup would be very helpful.

I like the A frame opening because it's easier to get in, but still it's awkward to get in and rotate feet around.

I think maybe next time I'm going to make something like a Trailstar, zipper opening, all edges on ground. This will weigh about the same.