Random thoughts: a case for smaller tree straps?

[SGT Rock]

I think I get what you are trying to say. Basically you should always use a 1" strap because it is better. If you want more wraps get a longer 1" strap.

But a few months ago at the UL hang there were some folks using mule tape, I think it was around 1/2" wide. My first thought was that it wasn't thick enough and was bad for the trees. But there was no tree damage and the person was using multiple wraps. So do I lecture the person for being a bad hammocker or do I need to figure out why it was working. His choice in gear was working well, and was defiantly not bad for the trees.

How many folks remember when hammocks didn't have straps? My first couple of Hennessy hammocks were before the strap idea started. If you tied to a tree with one or two loops you were going to leave a ring around the trunk of the tree. When Tom sent me a set of straps later, I immediately saw the advantage.

But before the straps came out, how did we protect the trees? We made a bunch of wraps around the tree and overlapped them. How is it that multiple wraps of a cord protected the tree better than one wrap of the cord. But multiple wraps of a strap is a bad model that has no merit? I think there is something to multiple wraps. I'm not sure what it is yet. I also know when I wrap a strap around a larger tree there is less pressure at a given point under the strap that when I wrap around a smaller tree. How much and why is what would be nice to know.

[XSrcing]

It also depends on the tree. My 1" wide straps leave marks in the bark of older pines which has me looking for some 2" seatbelt webbing. If I knew I wouldn't hurt the tree I would probably just use a length of 1/8" Amsteel.

[angrysparrow]

I think I get what you are trying to say. Basically you should always use a 1" strap because it is better. If you want more wraps get a longer 1" strap.

No, that's not what I said at all.

We're looking forward to test results.

[SGT Rock]

Research on winch design trying to figure out how to calculate this came up with this nuggets:

Calculating the crushing force is not difficult. Consider a 360 degree wrap on
the drum core. This will produce a pressure on the core equal to 2X the rope
tension spread over the area of contact. i.e. rope width times the
circumference. Each additional wrap on the first layer adds the same force.

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

So larger trees are like larger drums - less force per area, and the same thing with wider straps. There was an error in the original post that was later corrected:

I think you are confusing parallel with concentric wraps. 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.

So if I wrap the straps on top of each other, then there will be no lb/in^2 benefit (although there may be a padding effect) but if the wraps are parallel there will be a spread of forces. And if I design an experiment with parallel wraps and my scale is under all the wraps, then the force it reads will be the same as a single wrap, so to correctly read the force the scale needs to be under one wrap only.

[MDSH]

The difference between a greased pole (little friction) and a tree is bark (friction). One can string a line between greased poles if the angle of attack is 90* to both and there is no load on the line, discounting the line itself. As soon as there is load on the line or you figure in the line's weight the angle of attack allows gravity to work, the speed of collapse depending on the viscosity of the grease. I suppose that if one tightened the line enough it would squeeze out the grease and the pole might have enough friction to maintain the line.

For hammock camping we must strike a balance: use the friction of the tree's bark but in a way that is best for the tree. That means spreading load over the greatest surface of the bark. But the laws of nature work for us: the greater the surface the higher the friction and the least damage to the tree, at the same time, blessed sport that we have!

So the question is simple. What strapping spreads the load best?

If one were to wrap 50' of polyester cord over and over around the tree and through a rigid ring, then hang from the ring ...

Or use a wide nylon strap.

Polyester straps bear load only on the top edge of the strap, given the 30* angle of attack, because they do not give very much. They dig in rather than spread the load. Going from one 1" strap to two or three wraps of a 1/2" one is an improvement but it still digs on the top edge when loaded at a 30* angle to the tree, even if the vertical ridges of the bark allowed circular distribution of the load by breaking off the bark to fill voids between ridges.

But as I think about it, a longer but narrower nylon one wrapped two or three times would be ideal because it uses both SGT Rock's valid reasoning and the virtues of nylon, which conforms itself to rough surfaces better than polyester.

[Cranky Bear]

It also depends on the tree. My 1" wide straps leave marks in the bark of older pines which has me looking for some 2" seatbelt webbing. If I knew I wouldn't hurt the tree I would probably just use a length of 1/8" Amsteel.

To expand on this, SGT what model would you be using to determine possible damage caused by pounds of force and friction? As every tree is different, so testing would need to be done on every type of tree to determine how much (if any) damage/harm is caused! Unless there is a universal model that would/could replicate it for every tree? Steel vs Tree are two very different things.

Not being argumentative at all, as a fellow UL'er I am always looking for ways to lighten up and this sounds very enticing, but as AS said (well put differently) I want to make sure that this would be seen by "All" whom have no clue about hammocking as a "Safe" practice for LNT and not harming the environment (tree's).

[SGT Rock]

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.

[HappyCamper]

There I said it.

My favorite comment on this thread. Most of the rest is like . . . it's like . . . well . . . MATH!

[cvlngnir]

OK, I'm new to hammocking but not to engineering. SGT ROCK's theror is flawed I hate to say. The tension in you webbing decreases dramatically with the length of contact with tree trunk. Try this:

Wrap the webbing only 180 degrees around the trunk and have someone (or yourself if you like pain) sit in the hammock. Unless it is a really big tree you won't be able to win the tug of war.

Now wrap it another 360 degrees even without overlapping the wraps and sit down. You will be very close to supporting your own weight if you can't already.

This just shows that the tension transferred from the strap to the bark of the tree fairly quickly, so the extra wrap does little for you.

So the strap is putting a lot of tension (compression on the bark) very early so you want to have as much width of strap to distribute it as much as possible as soon as possible.

[MDSH]

Vertical ridges of the bark will prevent the equal distribution of the load through straps around the tree because of friction. If it was a greased pole then the load would equalize through the straps for the lack of friction preventing it.

My multiple wraps of 550-through-a-ring model above would put an equal amount of load on each strand because the rigid ring distributes the load equally to each strand. Then you'd have a proportionate decrease in the load on each cord for every wrap you add. Parcord has the quality of flattening out under such a load, which increases surfaces contacting upon the bark (friction) and thus bearing load. The more the load is spread on the bark (down to microscopic levels like the filii on the feet of geckos) the easier on the tree and more friction for us to hang on.