Bridge Hammock

**blackbishop351** · 06-18-2007, 16:49

To get a true catenary curve, you need something as close to perfectly flexible as possible - tent poles or wood molding aren't ideal. Probably doesn't make much difference for this application, though.

**headchange4u** · 06-18-2007, 17:01

Originally Posted by TeeDee

I'm using 1/2" wide polyester tubular webbing. Could only find tubular in 1/2". Will sew the webbing the whole length of the cat cut ends. Webbing arrives tomorrow.

Laid out the fabric yesterday and cut some bias tape out of the same ripstop. The bound edges will match the hammock body now. Using the bias tape on the edges of the open side.

Also, laid the hammock fabric on the floor and measured and cut the cat cut sides. Used fiberglass poles from chimney sweep brushes to get the cat cut arc on the ends. They flex well and set out the arc beautifully. Matched the dimensions in the Australian hammock exactly. Used tailer chalk to draw the arc along the poles. You probably could also use flexible tent poles or flexible wood molding.

Sewed the corner reinforcing patches and the bias tape on the open sides.

Just waiting for the webbing now.

Once the cat cut arc is drawn, the rest goes fast. Even less sewing than on my 12' HH style hammock.

Once I have the webbing sewn, will hang and test and start thinking about fitting bug netting and detachable fabric panels for head side and probably the foot side.

Please feel free to post any pictures and instructions that you want (that goes for anyone attempting one of these hammock)!

**slowhike** · 06-18-2007, 17:13

Originally Posted by headchange4u

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Something else that has crossed my mind are the ends of the hammock. The JRB hammock has fabric sewn on to the ends on the hammock to close of the the head and foot. Wouldn't this fabric limit how far the hammock could be spread open? If you are getting shoulder squeeze and needed to make the head end wider, say with a trekking pole or other method, the fabric end caps would almost need to be elastic or be adjustable in some other way.

This would be an easy fix in a DIY version because you could find the correct width at the top to eliminate shoulder squeeze for you and make a spreader bar and fabric end cap that fits that width. I don't know how this would be addressed in a production model. Everyone who tried the JRB hammock out agreed that it was very comfortable, but only some experienced shoulder squeeze while others didn't. That's of course because of different body sizes and shapes. I just wonder how this will be addressed.

smee told me that as they were considering a wider spreader bar they would also need to of course change the width of the end pieces of fabric to accommodate.

**TeeDee** · 06-18-2007, 17:14

Originally Posted by headchange4u

Please feel free to post any pictures and instructions that you want (that goes for anyone attempting one of these hammock)!

Yeah - I'm taking lots of pictures (film) as I progress. 7 more frames left on the roll - so I'll probably have some pictures to post soon.

**TeeDee** · 06-18-2007, 17:19

Originally Posted by blackbishop351

To get a true catenary curve, you need something as close to perfectly flexible as possible - tent poles or wood molding aren't ideal. Probably doesn't make much difference for this application, though.

True, but for this application, I think that uniform stress and mass homogeneity along the material is just as important to get a uniform curve. Although the poles I used had some pretty hefty connecting points in the middle and that didn't make any difference just eyeballing it. Not a true catenary curve, but close enough for "government work".

**rptinker** · 06-18-2007, 19:38

Originally Posted by headchange4u

I have been thinking about this design a little bit more. I think I would go with grosgrain on the cat cut edges, sewn into the roll hems like the Warbonnet "perimeter loaded" tarps for reinforcement. I think grosgrain would be a light weight way to reinforce the edges.

I have also been thinking about making the foot end narrower than the head for 2 main reason: Reduced weigh because you would be using less fabric and you would also be able to use a shorter spreader bar on the foot end (suggested by rptinker), further reducing weight.

Something else that has crossed my mind are the ends of the hammock. The JRB hammock has fabric sewn on to the ends on the hammock to close of the the head and foot. Wouldn't this fabric limit how far the hammock could be spread open? If you are getting shoulder squeeze and needed to make the head end wider, say with a trekking pole or other method, the fabric end caps would almost need to be elastic or be adjustable in some other way.

This would be an easy fix in a DIY version because you could find the correct width at the top to eliminate shoulder squeeze for you and make a spreader bar and fabric end cap that fits that width. I don't know how this would be addressed in a production model. Everyone who tried the JRB hammock out agreed that it was very comfortable, but only some experienced shoulder squeeze while others didn't. That's of course because of different body sizes and shapes. I just wonder how this will be addressed.

My two cents worth on cat cut hammock!

An adjustable spreader bar would be nice in eradicating shoulder squeeze. Probably, another spreader bar on the lower part of the fabric end cap would be more effective in eradicating shoulder squeeze altogether because it would define the shape of the hammock bed. If you want a wider wiggle room for your feet then another spreader bar on the lower foot end would solve the problem. But i believe three spreader bar would suffice.

**TeeDee** · 06-18-2007, 19:56

Originally Posted by blackbishop351

To get a true catenary curve, you need something as close to perfectly flexible as possible - tent poles or wood molding aren't ideal. Probably doesn't make much difference for this application, though.

I think that with the stressed pole, I'm really getting a parabolic curve and not a catenary. But then suspension bridge cables are parabolic and they're pretty stable.

Don't know that anyone has ever really studied the stretched fabric to determine the most effective curve. I think everyone just assumes that what is best for a free hanging cable/chain is best for the fabric edge.

**blackbishop351** · 06-18-2007, 20:14

No, I've actually seen an engineer's write-up on the force distributions in a situation with a flat, flexible material like we would want in a tarp. I can't remember exactly what the material was or where I saw it though. Anyway, the forces distribute themselves along the catenary, which is why longer tarp edges sag.

**funbun** · 06-19-2007, 01:13

I ordered my stuff today.

30 feet of 4.8mm Syderline
Hand sewing twine
Curved hand sewing needles

The rest I'll salvage from old hammocks. I'll try bamboo first, then make adapters for trekking poles later.

I plan to use velcro to seal the ends (bugnet verion and a ripstop version.

The tarp can be much shorter like 7.5 * 10 instead of 12 * 11. Probably just make it rectangular with cat cuts. Until I can make that, I'll just use my old Speer Style 10 *10.

Probably use the same Mirage style bugnet. Everything should be short/lighter with this hammock. The greatest weight threat is the spreader bars. So using treking poles is key.

**rptinker** · 06-19-2007, 02:40

Yo Funbun!
Ive just bought several yards of bridal satin for the hammock body and 1 1/2 inch nylon webbing for suspension. I plan to use the webbing instead of cord/rope for suspension becuse im not comfortable with handsewing like the austalian's. I guess, im still in the wait and see attitude and will wait for your show and tell!