SGT Rock

2012-08-27, 09:23

I posted this on HF, but I know some of my hammock buddies here avoid the place, so I'm posting it here too

Howdy all. I haven't been posting much because I have been working a ton of hours lately. It's nice to still have a job considering...

Anyhow, while I was working about 90 hours last week a spark of a thought crept into my head about tree straps. It was probably ignited by a set of Dutch's new Dutch Clips I got in the mail. And before I start I must say there is a good chance what I am saying isn't correct because I am not an engineer. It is also probably going to be a little controversial for some because it pokes at the conventional wisdom - but I do that a lot and have been successful with things other folks said would never work.

So this it: maybe 1/2" wide tree straps are better than 1" wide straps.

There I said it.

Now follow this logic. It may be flawed...

Imagine your single line load is about 200lbs and you have the choice to use A) 1" strap 6' long, B) 1/2" strap 12' long. They both weigh the same in this thought experiment, so there isn't any real weight advantage. The mass should also be about the same too, so no space savings inside your pack going either way. So which is better for the trees?

Ask me two weeks ago and I would have said A. Now I'm not so sure.

If your load is 200 lbs on the line, then the surface area of the strap distributes it over the outside of the tree. So if your tree is 22.93" in diameter, that means the circumference is going to be roughly 72". With strap A you can wrap it around once, which means you have 72" of surface area for the strap. That would be about 2.77 lbs/in^2 under the strap. Not bad for the tree at all. Lets say you used strap B but wrapped it around the tree twice - still 72" of surface area so the weight per in^2 is still the same. The 1/2" strap is just as safe for the tree, you just have to wrap more.

Lets say you are stuck with a tree 11.48" in diameter. The circumference is now just slightly over 36", so you can only get one wrap with the 1" strap, and the surface area is just slightly over 36", so you are now putting about 5.55 lbs/in^2 on the tree. Still not bad. But if you used a 1/2" strap you can wrap the tree three times! That means your area is now 49" of area and the weight on the tree is only 4.08 lbs/in^2 - the 1/2" wide strap actually protects the tree better than the thicker strap. Hmmm....

The math also has other interesting breaking points like at 7.7" diameter you put 4.15 lbs/in^2 with the 1" strap with 2 wraps max, but the 1/2" strap can get 5 wraps and is down to 3.35" lbs/in^2. At 45.8" diameter (that is a BIG tree) you cannot even begin to get around it without using some sort of extender, but the 1/2" strap can get around it once. And with all that area covered, it only puts 2.77 lbs/in^2 on the tree. A couple of weeks ago I wouldn't dream of hanging off a 1/2" strap on any tree, but now if I were to go to some redwood forest I would probably make some big honkin' 1/2" straps.

OK, so I admitted I am not an engineer, so there may be some flaw with my math somewhere. I know this also doesn't take into account for some overlap of the wraps which is going to happen at some points with either strap - so there is the real world factor that would change some of these numbers.

So what are your thoughts?

Howdy all. I haven't been posting much because I have been working a ton of hours lately. It's nice to still have a job considering...

Anyhow, while I was working about 90 hours last week a spark of a thought crept into my head about tree straps. It was probably ignited by a set of Dutch's new Dutch Clips I got in the mail. And before I start I must say there is a good chance what I am saying isn't correct because I am not an engineer. It is also probably going to be a little controversial for some because it pokes at the conventional wisdom - but I do that a lot and have been successful with things other folks said would never work.

So this it: maybe 1/2" wide tree straps are better than 1" wide straps.

There I said it.

Now follow this logic. It may be flawed...

Imagine your single line load is about 200lbs and you have the choice to use A) 1" strap 6' long, B) 1/2" strap 12' long. They both weigh the same in this thought experiment, so there isn't any real weight advantage. The mass should also be about the same too, so no space savings inside your pack going either way. So which is better for the trees?

Ask me two weeks ago and I would have said A. Now I'm not so sure.

If your load is 200 lbs on the line, then the surface area of the strap distributes it over the outside of the tree. So if your tree is 22.93" in diameter, that means the circumference is going to be roughly 72". With strap A you can wrap it around once, which means you have 72" of surface area for the strap. That would be about 2.77 lbs/in^2 under the strap. Not bad for the tree at all. Lets say you used strap B but wrapped it around the tree twice - still 72" of surface area so the weight per in^2 is still the same. The 1/2" strap is just as safe for the tree, you just have to wrap more.

Lets say you are stuck with a tree 11.48" in diameter. The circumference is now just slightly over 36", so you can only get one wrap with the 1" strap, and the surface area is just slightly over 36", so you are now putting about 5.55 lbs/in^2 on the tree. Still not bad. But if you used a 1/2" strap you can wrap the tree three times! That means your area is now 49" of area and the weight on the tree is only 4.08 lbs/in^2 - the 1/2" wide strap actually protects the tree better than the thicker strap. Hmmm....

The math also has other interesting breaking points like at 7.7" diameter you put 4.15 lbs/in^2 with the 1" strap with 2 wraps max, but the 1/2" strap can get 5 wraps and is down to 3.35" lbs/in^2. At 45.8" diameter (that is a BIG tree) you cannot even begin to get around it without using some sort of extender, but the 1/2" strap can get around it once. And with all that area covered, it only puts 2.77 lbs/in^2 on the tree. A couple of weeks ago I wouldn't dream of hanging off a 1/2" strap on any tree, but now if I were to go to some redwood forest I would probably make some big honkin' 1/2" straps.

OK, so I admitted I am not an engineer, so there may be some flaw with my math somewhere. I know this also doesn't take into account for some overlap of the wraps which is going to happen at some points with either strap - so there is the real world factor that would change some of these numbers.

So what are your thoughts?