Discuss - Guide to Making a Bridge Hammock

[Nightwalker]

I'm really comfortable...my next version will be aimed at taking it on the trail (lower weight, safe use of hiking poles as spreader bars).

Grizz

Have you tried extending the triangular ends of the hammock yet? It's a simple ratio thing on the math. just double the length to half the inward force on the spreader bars from that end. Increased height of the hammock body would do some more, but lengthening those triangles at the end would do the most, easiest.

I hinted about that in an earlier post, but thought about it a lot on my last hike. It's just an inverse fulcrum effect. Think about splitting wood with a wedge. With a 90 degree included angle, half of the force from the sledge goes into splitting the wood, half into driving the wedge. With a 45 degree included angle, 3/4 of the force drives inward and 1/4 goes into the split. This is just the same thing, but with pulling instead of driving.

Please excuse the clumsy wording. Some days my neuro damage shows more than others, and today seems like one of those days.

[GrizzlyAdams]

Have you tried extending the triangular ends of the hammock yet? It's a simple ratio thing on the math. just double the length to half the inward force on the spreader bars from that end. Increased height of the hammock body would do some more, but lengthening those triangles at the end would do the most, easiest.

I hinted about that in an earlier post, but thought about it a lot on my last hike. It's just an inverse fulcrum effect. Think about splitting wood with a wedge. With a 90 degree included angle, half of the force from the sledge goes into splitting the wood, half into driving the wedge. With a 45 degree included angle, 3/4 of the force drives inward and 1/4 goes into the split. This is just the same thing, but with pulling instead of driving.

Please excuse the clumsy wording. Some days my neuro damage shows more than others, and today seems like one of those days.

There's a lot of chit-chat in the Bridge Hammock thread about this and related issues. TeeDee and I had a conversation going about the most effective thing you can do in this line of thinking, which is to essentially remove the apex of the triangle, and run your suspension lines to either side of a wide tree.

That's fine and good and ought to be done when we can. When my rig goes into the woods I'm bringing long suspension lines! What I'm hoping for in the comment you cite is an approach that depends less on specific hanging context. Again over in the Bridge Hammock section, lemme see, here,
there's an analysis of a method that structurally suffers perhaps 1/3 the compression by putting the spreader lower than the suspension lines, being able to use a shorter spreader to achieve the level of shoulder squeeze.

cheers
Grizz

[headchange4u]

That's a great tutorial, Grizz. Thanks for posting it.

[GrizzlyAdams]

That's a great tutorial, Grizz. Thanks for posting it.

Thank you. I'm looking forward to you getting into the bridge hammock making business. You might have noticed I'm pretty excited about your idea of lowering the speader bars. The question just is, how to effectively do that?

Grizz

[slowhike]

Thank you. I'm looking forward to you getting into the bridge hammock making business. You might have noticed I'm pretty excited about your idea of lowering the speader bars. The question just is, how to effectively do that?

Grizz

i've not got around to trying this yet, but i've been thinking about it for a while now.
http://www.hammockforums.net/gallery...5/P8240001.JPG
don't know if it would be of any help to you in lowering the spreader bars or not, but you could use a spreader bar (trekking pole) at both ends rather than one like in the drawing. the side panels would be what stabilizes the hammock.
the bottom panel (green) just a little wider than the persons shoulders.
it has 1" webbing sewn to it's hem for strength & to capture the ends of the spreader bars.
just throwing out a thought. ...tim

[GrizzlyAdams]

In the the Guide I pointed out that with an occupant, the shape of an ellipse for the end-cap is off the mark. There's a picture that shows that it's a bit too short. The Guide points out that you could really approximate the shape formed by a regular shape with straight sides. I'm shy of dealing with those corners though, and so continued on talking about how to compute and use an ellipse.

This has bugged me a bit, and so I did some scratching around to see how tall the end-cap would be if I assumed it was a parabola, with the center and lowest point being the center.

So a parabola can be computed as the curve

y = alpha*x^2

where ^2 means "squared". What we know is the length of the fabric in the arc the parabola takes from corner to corner, e.g., 60". Call that L. This length falls along the curve though. In fact, half of it---L/2---falls along the curve from the center ( call this x=0 ) to the right edge (call this x=S/2, where S is the spreader bar length) .

If we know what alpha is, we can compute the so-called "arc length" of the parabola from x=0 to x=S/2. If you're an engineer you recognize this as a line integral, if you're normal then you're probably not reading this anyway.

I googled around to find an expression for the parabolic arc length. Found a derivation that assumes alpha=1; just going through the steps carrying alpha along, and assuming that the arc length of interest is from the center to one corner (i.e., x=0 to x=S/2) gives the formula

C = 0.5*L*Z + 0.5*ln( 2*alpha*L + Z )

where Z = sqrt( 1 + (2*alpha*L )^2)

This formula gives us a way to compute the arc length, for a presumed value of alpha. Problem is, we know the arc length we want, what we need is alpha.

The larger alpha is, the larger the formula value is, which means we can use what is known in computing as a binary search over a interval of possible values for alpha that is assured to contain the right answer.

So I did that, and found that (as hoped and expected) the parabolic curve is deeper than the ellipse. For a hammock that is 60" wide in fabric at the ends, with a 36" spreader bar, the ellipse has a depth from spreader bar of 20.13" while the parabola has a depth of 27.6". Shorten the spreader bar to 30", and the ellipse depth increases to 22.46" and the parabola to 27.96". The attachment shows a graph of the 36" spreader bar case.

So in my next version I'm going with a parabola.

Grizz

[GrizzlyAdams]

i've not got around to trying this yet, but i've been thinking about it for a while now.

didn't you quip somewhere that you need to do a project before going to the Sept. hang in Hot Springs? 3 weeks...plenty of time....

http://www.hammockforums.net/gallery...5/P8240001.JPG
don't know if it would be of any help to you in lowering the spreader bars or not, but you could use a spreader bar (trekking pole) at both ends rather than one like in the drawing. the side panels would be what stabilizes the hammock.
the bottom panel (green) just a little wider than the persons shoulders.
it has 1" webbing sewn to it's hem for strength & to capture the ends of the spreader bars.
just throwing out a thought. ...tim

yes, the ideas we've been kicking around involve doing something to secure a hiking pole to use as spreaders, and 1" webbing is a prime candidate.

In your diagram, what's to keep you from having the pole in your back? Not getting that part.

Grizz

[slowhike]

the person would be below the spreader bar (toward the center of the hammock), rather than laying on it.

[cameronjreed]

Uber great article. Thanks for taking the time and effort to put it together. Very nicely done. Great pictures and clear explanation. Can't ask for better than that.

[Kanguru]

I'm new here and this is my first post. Developed a much more intense interest in hammocks after sleeping on a particularly bad piece of real estate my last trip. Since I am a DIY person I am very happy to find this article. Have made my own tent and this is a natural progression. This design is really great. Thanks for great info!!!

Sam