DIY Enclosed Tarp
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
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.
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.
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)
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,