DIY Enclosed Tarp

Introduction

After spending some time ogling over the MLD Trailstar’s wind-cutting abilities and wondering how it could be made for a price that didn’t cost the earth, I set out to design a 1-person tarp. With plenty of spare time at the moment I designed this tent from the ground up.

Here’s a basic specification that I tried to stick to:

  • Must weigh less than 500g with guylines, stuff sack and stakes
  • Must be able to withstand constant 20m/s winds and 30m/s wind gusts
  • Must support borah bivy tie-out points
  • Must fit a 190cm human
  • Should be able to sit up comfortably without head touching fly
  • Should be able to get out of without crawling on ground
  • Must be no taller than 135cm, to support trekking poles
  • Should perform as well as or better than the MLD Trailstar

Design Process

MLD Trailstar Pitching Guide
Here’s what the MLD Trailstar looks like if you’re not familiar. It’s effectively a polar array of triangles to shape a hexagon. (Photo courtesy of Steven Horner)

The first step was to create a control for testing. This is a 3D model of the MLD trailstar with a low ground pitch, something favourable in windy conditions. This helped to compare material weight, dimensions and height.

The MLD Trailstar is actually quite difficult to construct at normal size due to the triangular panels being so large. These don’t fit on a conventional 150cm roll of material. After a few iterations of designs I ended up with this:

It’s a narrower design than the MLD Trailstar and features a zip entrance at the back.

From here the design was refined by sticking it in a virtual wind tunnel and improving on the dimensions. The goal was the get a good balance of space inside the tarp and aerodynamics, as well as amount of material used.

In the wind tunnel simulations with a 30m/s headwind the MLD Trailstar had a maximum pressure point of 41.0 Pascals and my tarp was showing as 40.1 Pascals. This number was only used to compare against the Trailstar.

The MLD Trailstar has a greater focus of pressure on the immediate corner, with a high falloff in spread of pressure. It should be noted that this configuration of the Trailstar is at a low angled pitch, with a trekking pole at 120cm. After designing the tarp to be more pointed, the aerodynamics improved dramatically. This ended up with a design resembling the Super Star Destroyer.

After some more tweaking and adjustments, trying winds at different speeds and angles I ended up with this:

Unfortunately the design didn’t quite fit on the 150cm material roll width:

I jumped over to Fusion and defined the measurements to a point that they could fit on a 150cm wide sheet. This was worthwhile and in retrospect starting the designs in Fusion instead of Rhino would have been a lot faster to make tweaks.

Patterning in Fusion was a lot easier than Rhino

Whilst still in Fusion I took a quick look to see what the material weight would roughly come to. The cumulative area = 68568.7674 (+/- 0.0013) square centimeters. If using 36g/m2 SilPoly, the tarp weighs 246g of core SilPoly. This is without seam allowances, fixtures, guylines etc.

Construction:

20D SilPoly and Mara 70 Thread
One of the hardest parts of the build: The Zipper

There aren’t too many construction photos due to them not being too interesting. The sewing was mostly just joining big slippery sheets of green fabric together. (Which was very tricky to work with)

Final Photos:

The tarp came together pretty quickly so I brought it with me on a morning trail run. Here it is pitched on a grassy field:

The important bit; how much does it weigh?

415g with excess guy-lines and a stuff sack.

Thanks for reading,
Benjamin

  • Post category:Gear

This Post Has 8 Comments

  1. Martin

    Wow, this came up great! I discovered your blog looking for a review about aricxi´s tarp (and cant found it, maybe you delete it?) but what i found was great! Keep up the diy´s projects and the trip reports! Cheers from spain

    1. Benjamin Davies

      Hi Martin,

      Thanks for the feedback! I did a recent cleanup of the website which is why the aricxi post isn’t there anymore. I removed that post as I wanted to encourage a focus on MYOG and DIY projects instead of getting tarps made for cheap in China.

      Anyway, there are certainly some more DIY projects incoming, with a running vest / fastpack up next.

      Have a lovely day,
      Benjamin

  2. Dan

    That’s freaking brilliant. Good stuff!

    1. Benjamin Davies

      Hi Dan. Thanks! I’m a big fan of your photography work and have just seen you’re into the MYOG game too now. Very cool 🙂

  3. Raul

    Hi Benjamin,

    Awesome stuff those backpacks! I discovered your looking for fabrics as I am in the sewing process of my own backpacks. Could you share some of your sources to procure different fabrics? I am having troubles acquiring the mesh fabric for the front pocket.
    Much obliged!

    1. Benjamin Davies

      Hello. For the front pocket I’d recommend a Polyester mesh, such as this one (if you’re from Europe):

      https://www.extremtextil.de/en/mesh-durable-polyamide-106g-sqm.html

      I used this on my 40L pack and it’s holding up great. Really strong and tough. If you’re after something a lot more stretchy you’ll want to use a Polyamide 4-Way Power Mesh.

      For Europe I can recommend Extremtextil and Adventurexpert as great sources for backpack materials.

  4. Tobias

    What program did you use for the wind tunnel simulation?

    1. Benjamin Davies

      Hiya! It’s autodesk flow design. Unfortunately I don’t think it’s available anymore as a single package, and is now a part of CFD ultimate. Best of luck 🙂

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