A few weeks ago I posted some pictures on Facebook that some of y'all may have seen. I made a truly huge winter tarp and there was a lot of positive feedback and requests for plans. So here's my write-up, but first some pictures.
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Like any good project this started out with a set of requirements.
- It had to fit my 12' hammock with room for my backpack hanging from one end
- It should be able to be fully enclosed, touching the ground along all edges
- The ridgeline should be as high as possible, while still having enough slope to leave head/toe room on the sides
- The hammock shouldn't need to be hung lower than typical (18" sitting height)
- To maximize the space inside, the doors would align edge to edge instead of overlap
With these basic requirements in mind, I started collecting information. My preferred hammock for comfort (not weight, but who's concerned about weight when they've got this giant in tow?) is a 12' long, 6' wide 1.7 oz Robic DIY. It's ridgeline is 117".hanging my pack from one end and leaving a few inches on the extremities I figured a 12' tarp would suffice. I didn't want to go longer than required because the longer the tarp, the higher off the ground it needs to be OR the shallower the hammock suspension needs to be. Hanging it higher is no bueno because of requirement #2 above. With this length, the appropriate sitting height, foot end raised by 4", and off center to leave room for my pack, the suspension needs to be no greater than 26 degrees from horizontal. This is assuming a tarp ridgeline height of some number, which also assumes some defined pitch of the side panels to reach the ground. In reality I went back and forth with all these variables until I found something suitable.
Next, with my hammock hanging appropriately in the basement and armed with a plumb bob, I started to mark how my body lays in the hammock so I could know how much room to the sides I needed. Hanging the plumb bob off my head, toes, and ends of the hammock I had somebody mark the ground so I could measure things out. Leaving a minimum of 2" from my body to the tarp panels (without poles) I calculated what the pitch of tarp needed to be. With this I started optimizing ridgeline height, suspension angles, and seam allowance.
Lucky for me I'm an engineer by trade and so have access to 3D modeling software. I drew up a model of the tarp, added in the measurements of my body and started playing with angles until everything fit. After I got something satisfactory, I then trimmed all the edges of the tarp even with the ground. This assured that the angles on the flat pattern were such that I would get a good seal to the ground.
After all that I ended up with this pattern. Feel free to use it and distribute it, all I ask is that it be attributed back to this post.
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As you notice in the pattern, I included seam allowances for the rolled hems and the flat felled hem on the ridgeline. The diagonal measurements for each vertex are to triangulate their position which is especially handy when laying out a large pattern to check that things come out square. I like to use a silver sharpie for dark colored fabrics like this because it shows up super nice. Once I have all the vertices marked I then take a straight edge and connect the dots. With a well marked line cutting it out with scissors is an easy task.
Sewing is pretty straight forward and I won't go into detail here other than to say buy a hundred or so sewing clips. They are far superior to pins and not a whole lot more expensive.
For the doors I hadn't quite decided how to hold them closed. They needed something since they were going to align edge to edge. Toggles were one idea, velcro another. In the end I found some small spherical (5-6 mm diameter), strong magnets that I decided to try out. I think they were from a bucky ball set, but I'm not certain. I put them under some reinforcement patches along the doors, two per door evenly spaced between the tieouts. I'd definitely suggest spherical magnets because they can freely rotate as needed to align to their mate. I'd also suggest going with the strongest magnets you can find since there's a fair amount of tension on the tarp.
Up to this point I hadn't considered using tent poles. I set the thing up in my back yard and was pleased to see that indeed all the measurements to the ridgeline and flushness to the ground worked out as expected. The side panels, though, weren't as taught as they could be (since I didn't use cat cuts). In still conditions this isn't too much of an issue. But once you get a good breeze then the panels start collapsing in, making the interior space smaller. Side pullouts was going to be my solution to this.
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Earlier in the fall I attended the Michigan Fall Hang and saw that several people had some internal tent pole mods on their tarps. I happened to have some aluminum tent poles laying around from a previous project, so I decided to give it a go. I played around with adding and removing sections until I had a length that worked well. This happened to be about 142". The poles need to be longer than the tarp is wide, but not by much. this will ensure there is tension all along the pole. The extra length can be dealt with by leaning the pole to either end of the ridgeline until it's a tight fit. I decided to lean mine toward the center, then I could hold them in place by tying a small line between the d-ring and pole.
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The poles did a tremendous job at opening up the interior space. This thing's a giant! To hold the pole ends in place I took some wide grosgrain and sewed on some pockets to hold the end. The tension of everything hold the poles in the pockets just fine.
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Eventually I will do away with the lines holding the poles in place and put in a pole clip or some velcro loops to do that job. Ideally I'll put them on the side panels in a location that doubles as an external tieout in case I want to shed the weight of the poles.
What's the weight of everything? Well, it's not a UL tarp, that's for sure. But it's still lighter than most tents!
Total weight: 1337g (47 oz)
Breakout of weight
Tarp: 712g (25 oz)
Ridgeline: 30g (1 oz)
Six stakes with guy lines: 110g (4 oz)
Poles in bag: 485g (17 oz)
Here's a Google Photos album with these and more pictures (will probably add more with upcoming trips) and some YouTube links. Enjoy!
https://photos.app.goo.gl/4Ih7u5tMoLurn2I53
https://www.youtube.com/watch?v=GkwuYg1hikE
https://www.youtube.com/watch?v=92vE0uto5dw
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