DIY catenary-line-supported dome shelter: details - Frank Groffie's miscellany

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Flysheet.  My particular flysheet was taken from a Wenzel® five-person dome tent bought around 2002. Who knows if this particular tent is still available; it doesn't matter. It was one of those huge family dome tents sprung with long fiberglass wands that could be had for about $120—and still can be; they're ubiquitous. Ours served us well for many nights over some 6 years until the sides of the main structure degraded and shredded under an onslought of sunlight. The flysheet, however, was seldom used and rarely saw sunlight and thus was essentially pristine and given new life in this project.

I erected it and measured and marked where I wanted to trim away excess from the edges. After trimming, I flame-seared the fabric edges and hemmed them (on my wife's grandmother's 1922 Singer). All seams on the flysheet were then sealed using commercial, toluene-based tent seam sealer.

Catenary suspension web. The flysheet was erected in test mode using the former tent's tensioned fiberglass tent wands to hold up and shape the central portion and using (new) guylines to hold out the edges. Once a satisfactory dome shape was achieved, and averaging along representative flysheet seams, and sketching using pencil on graph paper, I marked points on the flysheet seams where I wanted to attach vertical suspension lines.

At these points, I seared small holes (using a small nail heated in a torch flame) and inserted grommets. These grommets are those seen in shoes for shoelaces. They're available, with their installation tool, at most any crafts or fabric store.

I attached vertical suspender lines at each grommet. With the shelter erected in test mode, I erected guyed-out suspension lines over all eight of the seams between the eight panels of the flysheet and marked preliminary points along the suspension lines to rig the suspender lines. At each (preliminary) mark I tied a simple loose overhand knot and tied the vertical suspender lines, loosely, to the knots.

I then added a main vertical line, removed the poles, tightened up the lines, and left the structure for several hours to equilibrate (stretch). Finally, I tensioned the lines once again, adjusted locations of knots in the suspender lines, and adjusted the lengths of the suspender lines.

Vertical suspenders. Shown at right is a view of where the vertical suspender lines attach to the flysheet. Note how all attachment points are on seams of the flysheet. Near the top is an exterior view: the suspension line has been glued to the grommet. This glue is a dab of thermoplastic from a hot-melt glue gun, which serves two purposes: (1) keeps out water, and (2) eliminates free ends in the lines that could tend to produce tangles. Below is an interior view: a small leather washer distributes stresses over a slightly larger area than just the grommet and (2) prevents the knot in the line from pulling out, because, obviously, you've drilled a very small hole in the leather. The knot is a figure-8 knot. Ends of all lines are seared using a flame.

Pole-stake bottom tips. The bottom ends of all pole-stakes (right) are given little points made from short lengths of solid aluminum rod that are inserted and epoxied in place.

Tube for center pole. Shown below, right, is the fabric tube (made from leftovers) for the optional center pole. This tube is about 3 inches in diameter. It's been sewn into a spot very near the center of the flysheet. A drawstring closure is sewn to the top to minimize rain infiltration when a center pole is used or when not. All seams are sealed with appropriate sealant.

Tops of pole-stakes. Also shown below, right, is the hook near the top of a pole-stake. This hook gives an attachment point for the elastic band holding up the floor sills.

Not readily visible is a sort of plug, a short piece of solid aluminum rod inserted into and epoxied to the top end of the pole-stake. This plug gives the pole-stake a strong, blunt, solid top. A solid, sealed top (1) allows the pole-stake to be pounded into the ground without mangling the top of the tube and (2) keeps debris out of the tubing.

Several details are shown at right, including guyline stakes (eight minimum), main vertical line (approx. 50 feet), and one pole-stake.

The carry pouch, shown below, right, keeps the stakes and main line neatly packed and minimizes tangles in the line. The pouch also provides a convenient tool for slinging the main vertical line over a high tree branch. After the pouch is emptied of its contents, a rock may be placed in it. The main line is tied to the pouch, as shown. One then tosses the pouch, with rock, over the target overhead tree branch and ties the free end to a convenient low tree branch.

Edge gutter. A small portion of rain gutter tubing (black, lower left) is also shown. This tubing is ½-inch, flexible, slit tubing designed for wrapping bundles of electronic wires, available in bulk from your local electronics retailer. It attaches to the edges of the flysheet (edges inserted into slit) using aluminum pop rivets every 6 inches. You’ll need to sear small rivet holes in the fabric and tubing using a small nail heated in a torch flame.

I arranged for edge gutters on pairs of flysheet panels to merge and for a ⅝-in. conductor tube to take the runoff down two of the “corner” guylines to discharge points some 2 to 3 feet away from the shelter.

Floor. My floor is just 2-mil polyethelene sheeting, cut to a hexagonal shape and incorporating near-vertical sidewalls. The floor began as two large portions of poly sheeting joined and then then carefully measured and cut at the edges to make a complex hexagonal net, including floor sills. Joints in the polyethylene sheeting were joined merely using duct tape. At each of the (six) corners, a small hole was punctured (and given duct-tape-reinforcing) to accommodate a pole-stake. This floor construction was a cheap and less-than-durable substitute for a more-permanent floor, described below.

I chose a hexagonal shape for the floor partly because the flysheet wasn't a regular octagon with equlateral sides. Rather, the flysheet is oblong and approximates a hexagon. Also, the hexagonal floor shape minimized work when fabricating corners and associated parts for the floor.

I added (using duct tape) space-blanket material to the bottom of the floor to give it limited protection from punctures and abrasion and extend its life beyond just a few nights’ use. Again, this was an inexpensive measure, for proof-of-concept prototyping purposes.

A permanent, durable lightweight floor could be made from coated nylon fabric following the floor pattern described above. Seams for sidewalls would be sewn and sealed. Points where pole-stakes meet the floor could be provided with thick webbing and stitched reinforcing.

Packaging. Excess fabric removed from my former Wenzel tent flysheet was used to make a stuffsack, as shown above here. The final DIY product — including flooring, pole-stakes, guyline stakes, etc. — weighs 4.1 pounds and measures 8 inches in diameter by 14 inches in length (pole-stakes extending beyond notwithstanding).

It’s a sweet deal for a highly wind- and rain-resistant shelter that sleeps three comfortably.

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