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View Full Version : Random thoughts: a case for smaller tree straps?



SGT Rock
2012-08-27, 10:23
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?

Hog On Ice
2012-08-27, 10:59
seems to me I remember a discussion of the use of a hollow braid support line which was approximately 1/2 inch wide when flattened around a tree - discussed early on in the history of recent hammock camping - in the '01-'03 time frame if I remember correctly. Unfortunately I don't remember any of the points of the discussion nor any reason why that approach was dropped. Unfortunately the use of the 1 inch wide tree straps has turned into part of the religious credo of the Hammock Koolaid Drinkers Church.

With respect to the distribution of force on the tree - I am of the opinion that the force is somewhat more on the side of the tree away from the hammock and somewhat less on the side toward the hammock but I am also of the opinion that this is almost a don't care wrt the comparison of half inch double wrap vs one inch single wrap configuration

SGT Rock
2012-08-27, 11:21
seems to me I remember a discussion of the use of a hollow braid support line which was approximately 1/2 inch wide when flattened around a tree - discussed early on in the history of recent hammock camping - in the '01-'03 time frame if I remember correctly. Unfortunately I don't remember any of the points of the discussion nor any reason why that approach was dropped. Unfortunately the use of the 1 inch wide tree straps has turned into part of the religious credo of the Hammock Koolaid Drinkers Church.Exactly. I remember being told dynaglide was too thin for hammock suspension. UCRs don't work, 1.1 single layer is too thin, footboxes don't work, etc. I remember when Sil-Nylon was going to get hikers killed because it was too flammable. Alcohol stoves were no good for winter hiking, etc etc etc.

I'm sure I will get a dozen opinions why it won't work over there. But I'd like to design an experiment that would actually prove it one way or another.



With respect to the distribution of force on the tree - I am of the opinion that the force is somewhat more on the side of the tree away from the hammock and somewhat less on the side toward the hammock but I am also of the opinion that this is almost a don't care wrt the comparison of half inch double wrap vs one inch single wrap configuration

I also think you are right on that one, but I think the more wraps you have, even wraps over other wraps, the less that force actually is. I could be wrong.

Ray
2012-08-27, 11:25
Seems to me that for static loads the diameter wouldn't matter much - within limits I mean, we can agree that piano wire would be bad for trees - but friction due to rubbing would be bad and if that occurs then larger diameters would lessen the damage more than smaller diameters.

SGT Rock
2012-08-27, 11:29
Well that does sort of stand as the model. The original Hennessy and others used lines. Lets say 7/64th since that is a standard. A single wrap around a skinny tree would mean you only had about .109" x 32" = 3.49" of area and 200 lbs of pressure on it at about 57.3 lbs/in^2. A single wrap would scar up a tree. To prevent damage you would make multiple wraps (anyone besides me remember these days?). So if that works for a cord, why not the same for straps?

SGT Rock
2012-08-27, 12:27
I found this in a discussion about calculating crush force on the drum of a winch:


If I make a single wrap of rope around the drum the produces a pressure of, say, 2000 PSI on the drum, 20 parallel wraps still only produce a pressure of 2000 PSI, they just spread the pressure out over a wider area. Concentric wraps (layers) are additive, 10 layers would apply a pressure of over 10X the pressure applied by a single wrap, or upwards of 20,000 PSI.

Based off what I read there - if I made one wrap around a tree at 200 lbs, that would be about 200 lbs force. If I make 10 parallel wraps, that would still only be 200 pounds of force divided by 10, so 20 pounds per wrap. If you designed a test where all the wraps went around the scale, then it would still read 200 pounds, but if you designed the test where the scale was only under one of the wraps, you would get the force per wrap calculated. If the wraps are all on top of each other, then the force is going to be the same as a single wrap.

SGT Rock
2012-08-27, 12:29
From that same thread:


Playing with the above formula, it becomes clear the smaller drums see higher forces. Smaller rope diameter also generates higher forces.

Basically what I was looking at with width and tree diameter.

SGT Rock
2012-08-27, 13:48
Initial test. Not very scientific.

I've done a couple of initial tests using Mustardman's idea within the limits of the equipment I have. I really don't think this is proof that it works, but it does point out that this may be possible.

In test one I used a digital scale and didn't put anything in the hammock. With one wrap the weight came out at 11.22 ounces. With two wraps it was 5.37 ounces. I don't think this is an accurate indication of the weight on the strap at that point, but it does reflect a shift based on the number of wraps.

For test two I wanted to give it something to work with I put a liter of water in the hammock. With one loop the measurement was 28.3 ounces, and two loops measured at 18.62 ounces.

The wraps by no means were perfectly spaced, and the tree was fairly small since I had to get multiple wraps and a scale in there - and all these used 1" straps since that is all I have. I don't have any 1/2" straps to compare with at this point, but that will be the next step as soon as I get my hands on some mule tape.

Ray
2012-08-27, 14:03
Y'all are getting way too scientific, nobody cares about pressures and such. You need a visual demo. Use a cluster of beer cans to simulate a tree, say one in the middle with six more spaced around it and held together with a wrap of duct tape. Repeat the experiment, using new cans each time of course, and compare how much the cans are crushed with different configurations.

Should have a definitive answer after a case or two if anybody can remember the results.

SGT Rock
2012-08-27, 14:56
Beer isn't my thing. Will bourbon bottles work?

SGT Rock
2012-08-27, 14:59
By the way Ray and HOI, y'all are a lot more educated than I am, so I defer to your knowledge. In case you are looking for a model on what I think best represents this, it is called hoop stress as best as I can tell.

Ray
2012-08-27, 22:27
If the strap is wrapped very loosely around the tree, like a sling, then the hammock is hung from all of the ropes or most of them - see the "wrap 3 pull 2" (http://www.mazamas.org/your/adventure/nw/wrap-3-pull-2-about-the-strongest-anchor-you-can-build/) rock climbing anchor. That distributes the load equally across all lines around the tree. Is that what you meant?

In that case more wraps with a smaller diameter rope or strap could exert less force at any point on a tree than fewer wraps with a bigger rope. Depending on rope thicknesses, number of wraps, diameter of tree, and all that.

But if you wrap the lines tightly around the tree then the max force on the tree, in fact almost all the force, will be on the first wrap. The extra wraps bear less and less weight and after 3 wraps there is almost no tension on the rope. Depending on friction between the tree and rope, how much ice or mud is involved and all that. In that case the pressure on the tree directly depends on the rope diameter, extra wraps won't matter much. It's illustrated in the climbing anchor called the "tensionless hitch". (http://www.onrope1.com/Myth4.htm)

Does that help?

Skidsteer
2012-08-27, 22:38
Yes. I think I can hang a hammock from a bourbon bottle without breaking it now.

Big Mac
2012-08-27, 23:19
Yes. I think I can hang a hammock from a bourbon bottle without breaking it now.

you a funny man

SGT Rock
2012-08-28, 03:04
That top diagram is probably the best example of what I am looking for, though the idea is to not need to tie the hitch on the strap - the strap could use some sort of joining system in place like a Dutch Clip, the second example is probably what can happen if you do it wrong.

Two Speed
2012-08-28, 09:33
Yes. I think I can hang a hammock from a bourbon bottle without breaking it now.The hammock or the bottle? Breaking one is inconvenient, breaking the other is a tragedy.

Hog On Ice
2012-08-28, 10:12
tragedy and alcohol abuse

Cuffs
2012-08-28, 11:58
See. You really gotta make a clearer title for your threads. I thought you were going to make a case in which to carry your straps IN...

All this other BS is just that. BS. And way too much math. It's makin my head hurt.

Spogatz
2012-08-29, 10:24
what would the load per square inch be on piano wire?

Hog On Ice
2012-08-29, 10:29
how may wraps?

Ray
2012-08-29, 10:42
what would the load per square inch be on piano wire?Well, you do have to be more specific. Which note?

SGT Rock
2012-08-29, 20:20
I spent the night up at campsite 30 in the Smokies and had a great time. The rest was much needed! While I was up there I saw some tracks for the nuisance bear that has campsite 24 closed, and played with my multi wrap hammock hanging idea.

http://hikinghq.net/forum/attachment.php?attachmentid=4297&d=1346281852
Bridge over the little river

http://hikinghq.net/forum/attachment.php?attachmentid=4291&d=1346281779
closed trail sign

http://hikinghq.net/forum/attachment.php?attachmentid=4290&d=1346281752
Husky Branch Cascade (I think)

http://hikinghq.net/forum/attachment.php?attachmentid=4292&d=1346281790
"Dummy" tent to draw in the bear

http://hikinghq.net/forum/attachment.php?attachmentid=4293&d=1346281806
Critter cam watching the tent.

http://hikinghq.net/forum/attachment.php?attachmentid=4294&d=1346281817
Bear prints in the mud

http://hikinghq.net/forum/attachment.php?attachmentid=4295&d=1346281830
Two wraps for the hammock suspension.

When I got home, my mule tape was here, so I banged out a couple of straps for testing:

http://hikinghq.net/forum/attachment.php?attachmentid=4298&d=1346281862

http://hikinghq.net/forum/attachment.php?attachmentid=4299&d=1346281873

Hog On Ice
2012-08-30, 09:45
does the mule tape stretch much when first used?

SGT Rock
2012-08-30, 17:25
I don't really know yet. I haven't done a true load test. I plan to mark the straps where they pass through the clip before I use it the first time so I can see if they stretch.

You want 100' of 1250lb mule tape? I got 300' of it.

Skidsteer
2012-08-30, 18:58
Mule tape doesn't stretch much in my experience.

The big problem is that it's impregnated with slickum to help it pass through conduit. Various knots and attachment points tend to slip because of it.

I've wondered if washing it would help but never tried it.

We use it at work so if anyone needs small amounts, ask me first before buying it. I might be able to set you up.

SGT Rock
2012-08-30, 19:15
I think the guy I got it from must wash it, because there isn't anything on it.

tramp
2012-08-31, 02:17
Well,, I think you all are a lot smarter than me on this, as I am just getting into this hammock thing but I think the tree is dam tough and don't really care. Like a horse don't care what kind of saddle you put on him, just how heavy the rider is. If you are a 150lbs, what diff.does it make? If you are a 300lber then I can see your point. Maybe I just not looking at this from the right place.

shadowmoss
2012-08-31, 10:22
Well,, I think you all are a lot smarter than me on this, as I am just getting into this hammock thing but I think the tree is dam tough and don't really care. Like a horse don't care what kind of saddle you put on him, just how heavy the rider is. If you are a 150lbs, what diff.does it make? If you are a 300lber then I can see your point. Maybe I just not looking at this from the right place.

That. Yes, it does matter. Trees are not that tough. The living layer is the one right under the bark. Damage that and you can kill the tree. Maybe not right then, and maybe not the first time. But, as more and more people get into hammocking it makes a serious difference. If we want parks and such to let us hang from trees, we need to police ourselves to be as responsible as possible in taking care of the trees.

Superman
2012-08-31, 10:54
That. Yes, it does matter. Trees are not that tough. The living layer is the one right under the bark. Damage that and you can kill the tree. Maybe not right then, and maybe not the first time. But, as more and more people get into hammocking it makes a serious difference. If we want parks and such to let us hang from trees, we need to police ourselves to be as responsible as possible in taking care of the trees.

Oh twiddle....just kill all the trees so everyone has to tent...as god intended.:angel:

shadowmoss
2012-08-31, 11:26
shadowmoss smacks Superman. Oh, wait, he likes that.

tramp
2012-08-31, 21:37
Your right ! And I'm glad there are folks like y'all to fig. All this out. Sorry .

shadowmoss
2012-08-31, 22:10
No harm, no foul.

JDBaughman
2012-09-01, 00:50
Oh twiddle....just kill all the trees so everyone has to tent...as god intended.:angel:

Hahaha gotta remember your roots...


I <3 (. Y .)

Roots
2012-09-01, 01:34
Hahaha gotta remember your roots...


I <3 (. Y .)

Did you just say 'roots'?

JDBaughman
2012-09-02, 22:03
...lol

Hog On Ice
2013-02-04, 11:17
I think the guy I got it from must wash it, because there isn't anything on it.

Where did you get the mule tape? I see a lot of it on Ebay but I can't tell if any of it is washed.

SGT Rock
2013-02-04, 13:12
I got it from this supplier: http://myworld.ebay.com/bargainsaplenty?_trksid=p2047675.l2559

SGT Rock
2013-02-04, 13:12
I've got more if you need some.

Hog On Ice
2013-02-04, 13:27
thanks but at the moment I am OK - just wanted to file the info just in case I find I am using a lot of it

Hog On Ice
2013-02-04, 14:33
having recently found this thread again I had a thought as to how to more evenly distribute the force over the multiple wraps of the mule tape around the tree - I figured there had to be a multiloop knot that did not slip in mule tape and I think I have found one - see attached image from ABOK - the Portuguese Bowline knot - basically do the wraps loosely around the tree then tie a bowline over top of the loops - the only tricky part to the knot is putting the loop in the standing part - follow the diagram on the left for 1072 then put some tension on the end and the loop will transfer to the standing part then go and tuck it like a normal bowline (right part of 1072 diagram).

http://hikinghq.net/forum/attachment.php?attachmentid=4689&d=1360002641

SGT Rock
2013-02-04, 14:39
I'll have to try that

Sent from my SCH-I500 using Tapatalk 2

Hog On Ice
2013-02-04, 14:46
good video :

YdCu0wHRdiQ

Hog On Ice
2013-02-04, 14:48
a alternative way to tie the Portuguese Bowline: http://www.marinews.com/bait-presentation/portuguese-bowline/454/

another video of alternative method:

utAUtVmkdOo

Razor
2013-02-06, 11:27
By the way, for all you HH there is talk in the GSMNP office that there is a pattern of tree damage at some campsites and they are monitoring it and considering compiling rules to save the trees. Give them imput on the front end ------------

SGT Rock
2013-02-06, 11:29
Where did you hear that? I just heard that they came out with rules about hammocks in shelters but nothing about tree damage. I hike in the Smokies all the time and don't see any. I do see tree damage from horses.

hoodoo40
2013-04-06, 12:12
Just reading this thread for the first time. I r enngineerr and sometime I even know what I'm talking about. If the hammock load is 200 pounds, then half the load would go to each tree, so 100 pounds to each tree. So in the first posts, you would just need to divide by two for most of the numbers. (of course in designs we like to throw in safety factors of 2 or more, so 200 would work).

When you wrap the tree, most of the force will will be split to both ends of the straps, one on each side of the tree. (now in the mule tape picture, maybe more would go to the side without the buckle). As you get more wraps, the inner wraps would take less of the weight due to friction on the first wrap or two. So I think the wider strap would be better for smaller trees, while more wraps would be better for bigger trees. Of course, for bigger trees your also spreading your load over a bigger area.

Hmmm, maybe we should get a Gov't grant to study this problem. $50 million ought to do it. We could spend months testing hammock wraps on various trees in various national forest. Hmmm. Sorry, if you're a tent dwelling, there wouldn't be any funding available for you in the study.

Happy Camping, John