Bridge design questions

**GrizzlyAdams** · 01-01-2008, 00:27

OK I thought that when I hung the bridge hammock, I could just make a loop of cord from one side to the other (from the side with the hiking pole handle to the side with the hiking pole tip), then just clip it with a carabiner to the main suspension line, so the two sides would be self equalizing in length (brilliant - NOT). As you guys probably already know this is a bad idea! LOL When I try to get in, all the cord slides to one side and you can't get the thing level again without some major struggling, then once your level if you turn over, the cords slide and try to dump you out.

So my question is, what is the best way to do this? Seperate measured cords to a ring, then attach the ring to the main suspension line? I thought this would be the simple part but its harder than I planned, I wanted to make it simple to hang but not sure how to do it yet?[/QUOTE]

Take that same cord, and at the mid-point lark's head it onto something like a ring, or a carbiner. The lark's head will keep the two sides from moving.

Originally Posted by greggg3

I've read a bunch of comments about how big the triangle needs to be to protect the compression on the hiking pole, but I'm confused. When Grizz says 4' is that 4 feet from the corner (like the handle of the hiking pole) to the vertex (where it joins the main suspension line)? If so, then how far apart do the trees have to be, like 14 or 15' I guess? Or is it 4 feet from the handle end to the pointed end? I don't want to trash my hiking poles but I'd like to be able to hang from tress that are closer than 14' apart, is that possible?

4' from the pole end to where the two side lines come together.

You can hang from trees that are closer, but then you need to use stakes and pull-out lines to pull the ends of the hammock apart to get the flat lay. I did a post on that this fall. It's probably easier to find trees that are far enough apart.

Right now I'm using small suspension triangles, somewhat gingerly, for the sole purpose of getting my suspension entirely under a 10' ridgeline so that I can button the hammock up in a tarp-tent in the winter. 36" spreader bar, and 27.5" suspension side. It's really important to get the poles centered so that the compression force goes straight down the middle. But TeeDee has evidently been doing this for a while, and the JRB BMBH has spreader bars that are similarly scaled for smallish suspension triangle. Time will tell.

Grizz

**Walking Bear** · 01-01-2008, 15:04

I'm working on keeping the entire length down to just under 12 feet so that I can get it under a 12 foot ridge line tarp. That's longer than some. However, with my weight I wanted longer sides on the suspension triangle to reduce the stress on the poles. That's part of the reason I'm going with the spreader supports back about a foot from the ends of the hammock. At this time it looks like I can get a 38" spread with the poles and not need any more than the locking devices that are in the poles.
Nice thing about bridges is that there are lots of ways of getting them to work.

**greggg3** · 01-01-2008, 17:54

So far so good as far as stressing the hiking poles, I have them set at 41 inch spread, and the sides of the suspension triangle are 32". Another stupid question, is it the depth of the side cut ( I cut 6" in from each side) that affects how much tension is required to get the hammock to lay flat? I find that I have to string it really tight to get it flat, and cant really get a reverse banana no matter how tight I pull it. I was thinking maybe I didn't cut the sides deep enough?

**Walking Bear** · 01-01-2008, 20:19

Originally Posted by greggg3

So far so good as far as stressing the hiking poles, I have them set at 41 inch spread, and the sides of the suspension triangle are 32". Another stupid question, is it the depth of the side cut ( I cut 6" in from each side) that affects how much tension is required to get the hammock to lay flat? I find that I have to string it really tight to get it flat, and cant really get a reverse banana no matter how tight I pull it. I was thinking maybe I didn't cut the sides deep enough?

I can't put any math numbers to it. But I think that the depth of cut will make a great deal of difference. The 6" cut will take more tension to hang flat than a deeper cut on the sides. It will take a lot more tension to get the inverted banana. The additional tension will put more stress on all of the suppension components and spreaders.

**GrizzlyAdams** · 01-01-2008, 23:56

A shallower cut will make it harder to create an inverted banana, there's just less slack to bring up as you pull out on the suspension lines. A shallower cut also creates more force on the webbing itself, but it can take it.

I don't think of pulling more or less on the suspension to make it flat so much as I do finding the right separation between suspension triangle apexes and arranging that that is the distance they're at when I hang.

I use a main suspension line that has the ridgeline with this set distance in the middle---the endpoints of the ridgeline are tied to rings, and the apexes of the suspension triangles connect to these rings. Also tied to each ring is a heavier duty suspension line that goes to the tree.

I originally tried putting this line up and tightening it up before hanging the hammock. The more I tightened up, the less the rings drop and come together (making more sag in the hammock), but also geometry is working against us in increasing the force on all the lines involved because of shallow angles. When I snapped a single strand of 2.8mm Spyderline it was doing exactly this. Landing on your butt gives you cause for pause...what's wrong with this picture?

I came to realize that all I really want is to keep those rings at the proper distance, and I could let my own weight do what I was trying to do by tightening up the line. So I can achieve the desired effect by attaching to the tree high, making a significant angle at the ring between the ridgeline and the suspension line to the tree. See the attached photo. The suspension ridgeline is under the tarp (the other rideline is the tarp's own).

The way I found the right length for my ridgeline was to do a little geometry. The ridgeline length is the sum of (a) the length of the hammock from spreader bar to spreader bar, with (b) twice the horizontal projection of the suspension triangle's height, assuming a 30 degree angle of inclination. In your case the suspension triangle height is
h = sqrt ( 32^2 - (41/2)^2 ) = 24.57 in
Multiply this by cos (30) = 0.866 to get 21.25 in.

So, for example, if your hammock was the length of mine (80 inches) then
your ridgeline ought to be about 122.5 inches. This will just get you close, you can either lengthen the ridgeline or shorten the suspension line to pull the hammock out farther for better flatness if needed.

Grizz

**schrochem** · 01-02-2008, 08:31

Grizz, I've been way too busy with work to play with my bridge, but try to keep up with all the 'improvements' lol.
I see you went back down to 80" and I believe that was in order to minimize length for tarp reasons. How does this affect stomach sleeping with your arms over your head?
My first was 80ish and it was just a bit small for comfort. I'm 6'3" and enjoy the 96" length but admittedly haven't had time to work with messing with tarps.
Hopefully work will slow down and I'll find some time soon.

**GrizzlyAdams** · 01-02-2008, 09:54

Originally Posted by schrochem

Grizz, I've been way too busy with work to play with my bridge, but try to keep up with all the 'improvements' lol.
I see you went back down to 80" and I believe that was in order to minimize length for tarp reasons. How does this affect stomach sleeping with your arms over your head?

Mostly I don't do it that way. On my stomach I lie with my arms next to or under me. This isn't due to length so much as width and flatness. Tradeoffs. I cut this hammock narrower (53" before hemming) to make it flatter for a given spread of 36". My objective for winter camping has been to get the hammock buttoned up inside the tarp (with doors). That objective adds some real and challenging constraints.

Grizz

**greggg3** · 01-05-2008, 14:55

Grizz it sounds like I'm repeating what you did when you broke the spyderline, but swear I don't understand your solution, or how its working.

Basically to get the hammock flat when I'm laying in it, I have to really pull it really tight (so its actually reverse banana before I get it). But then when I lay in it, it sags down to a reasonable height and ends up flat. It just that it seems like I'm really stressing the support lines. In other words to end up with my body about 24" above the ground and laying flat, I have to really tighten up the tension to the trees and the support webbing on the hammock is about the level of my chin (with the spreader bars in), of course when you go to get it, the one side goes down, the other up, but I'm still up on my toes to get my arse over the webbing. So far nothings snapped but I'm a little uncomfortable pulling it so tight (maybe I'm just used to the ENO where its got lots of sag).

Anyway, can you try again (I"m evidently really thick headed) to explain what your doing so that your reducing stress on the lines? I mean I see that the ridgeline lets you always have the same distance, but don't you still have to tension the whole thing really tight, or else it sags, and the ridge line goes limp? Your ridgle line goes from ring to ring right?

I"m using 32" on each line from the point at the spreader bar to the ring, the spreader bars (hiking poles) are set for 41" of spread. They seem OK, i.e. when I'm lying in the hammock, I can reach and feel them to judge the load, they're not close to buckling and have never slipped at the clamps. I'm more worried about the support line being so tight. I'm starting to wonder if I should have cut the center down 10" on each side instead of just 6"?

**GrizzlyAdams** · 01-05-2008, 18:17

Originally Posted by greggg3

Grizz it sounds like I'm repeating what you did when you broke the spyderline, but swear I don't understand your solution, or how its working.

Basically to get the hammock flat when I'm laying in it, I have to really pull it really tight (so its actually reverse banana before I get it). But then when I lay in it, it sags down to a reasonable height and ends up flat. It just that it seems like I'm really stressing the support lines. In other words to end up with my body about 24" above the ground and laying flat, I have to really tighten up the tension to the trees and the support webbing on the hammock is about the level of my chin (with the spreader bars in), of course when you go to get it, the one side goes down, the other up, but I'm still up on my toes to get my arse over the webbing. So far nothings snapped but I'm a little uncomfortable pulling it so tight (maybe I'm just used to the ENO where its got lots of sag).

Anyway, can you try again (I"m evidently really thick headed) to explain what your doing so that your reducing stress on the lines? I mean I see that the ridgeline lets you always have the same distance, but don't you still have to tension the whole thing really tight, or else it sags, and the ridge line goes limp? Your ridgle line goes from ring to ring right?

I"m using 32" on each line from the point at the spreader bar to the ring, the spreader bars (hiking poles) are set for 41" of spread. They seem OK, i.e. when I'm lying in the hammock, I can reach and feel them to judge the load, they're not close to buckling and have never slipped at the clamps. I'm more worried about the support line being so tight. I'm starting to wonder if I should have cut the center down 10" on each side instead of just 6"?

There are interactions between the distance between trees, the height at which you attach to the trees, and the length of the lines from ring to tree.
You want to pitch high on the tree to get the lower force angle. Your ridgeline typically won't be tight. If you go "too high" it won't even be flat. But an easy thing to do to get control of the situation is, at each end, to add an additional line from the ring to the tree, more or less flat. Using these you can tighten up the ridgeline a lot, but still have the main suspension line take a nice sharp angle up to the tree. Now when you get in the ridgeline won't sag so much.

Now all the tension that is on the suspension line is due to weight, and so you're safe w.r.t. forces on the webbing.

give it a try. I carry around the extra line to do this very thing. Makes set-up simpler.

Grizz