Tuesday, February 26, 2013

Trapezoid Poncho Tarp

Poncho Tarps are kind of like mermaids: When you want a girl, you have a fish. When you want to eat fish, you have a girl. They are a compromise between raingear and shelter. But that compromise does come with a weight advantage (8 oz). On the gripping hand, here in the arid inter-mountain west, rain isn't all that common. When you get 18" of precip in a year, the likelihood of it raining 12" during your trip isn't that great.

This poncho features a neck collar instead of a hood. I always hike with a brimmed hat, and find a hood restraining and sweaty. Plus a collar is much easier to sew

Catenary or flat tarp? I like a flat tarp because it can be pitched in a variety of ways. This tarp uses a trapezoid cut which is flat, but 6' wide at the head end. It also features corners that are cut back for a tighter pitch (pseudo catenary)

The tarp is designed to be used in an A-frame pitch, or in a 1/2 pyramid pitch, or pitch using a bicycle as support.

Sewing the Trapezoid Poncho Tarp:

Materials and Sources
I used 1.4oz silnylon from Backwoods Daydreamer DIY Gear supply for the bargain basement price of $5.50 per yard. I had some matching silnylon on hand from an old project (about 2'x2' total, but scraps are fine). I also used a few feet of 3/4" grosgrain, and a bunch of thin cord for the tie-outs.

Step by Step
Lay out the fabric on the floor.
Cut it to 3 yds long (9 feet)
Measure down from one corner 24". Measure up 24" from the opposite corner (graphic 1)

Draw a straight line between these two points. Cut it out.
Flame sear all edges.
Flip one cut piece around and stack. Pin. Sew a flat seam. Sew a rolled seam down the middle with two lines of stitching. (graphic 2)





Lay it back on the floor, notice that the front corners are angled back from the ridgeline, but the rear corners angle the wrong end. Cut 6" back (see graphic 3)


Sew a rolled seam around the perimeter of the tarp
Cut two 6" strips of grosgrain. Fold over and sew to the ridgeline (picture)

Cut four 8" strips of grosgrain. Fold and pin them into right-angles Sew around their perimeters and secure them into the tarp corners. (picture)

Cut two 6" strips and two 2" strips of grosgrain. Sew them along the side midpoints. (Picture)

Side ties
Sew two more small loops of grosgrain at ______________ along both sides. These will be used to tie the poncho together for rain-gear use, and to add a few more options when pitching as a tarp. They are not full-strength tie out points.

Sewing the collar

lay out a scrap of silnylon 10" by 27". Sew a roll hem along the top edge for a drawstring. Sew the ends together with a 1/2" seam allowance.


Hood Option
Of course, instead of a collar you could create a hood instead. Use a hood pattern like this one. Or just copy the hood pattern from a hooded sweatshirt. Regardless of which you choose, the next steps are the same.

Locate the center of your tarp (Poncho-to-be), make a mark with a sharpie.
Use your seam ripper to carefully pick apart the seams at the middle of the tarp for 7" in either direction.
Now the tricky part: insert the collar into the opening in the tarp. Use lots of pins to secure it in place.

Sew around the poncho and collar so that the seam is inside the poncho. Getting the ends of the collar stitched down smoothly into the seam is really tricky. Try to get it as tight as possible, and don't be afraid to rip it out and do it over. (Picture)

Stretch the tarp out along the ridgeline. If you have puckers or bunches along the ridge, now is the time to rip them out and do that section over.

Stuff Sack

Almost done! Stuff your poncho into a walmart sack as tightly as you can. Scrunch it up good. Roughly measure the stuffed dimensions. Double the width and add 2" , add 3" to the length.  Sew a rolled hem for a drawstring channel into the top. Fold it over and sew the side and bottom.


Turn it rightside out. String the drawstring. Stuff it full.
DONE

(Pictures)

Results
Weight: 9oz
Cost: $17.50
Time: 4 hours (including some sewing machine trouble)


2 comments:

  1. Do you have any pictures of your poncho tarp in use? Would you use this shelter during buggier weather?

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    Replies
    1. I have pictures of the tarp set up. I think it looks like every other poncho tarp when pitched, a little taller on 1 end. For bugs, I use a bug bivy. See my post.

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