Measurement and calculation or practice and theory

**dirtwheels** · 06-18-2012, 12:00

Newbie questions here! From the outside looking in it would seem that the weight supported by the tree straps would be roughly 1/2 of the weight of the hanger and suspension. Picture 2 guys holding up a girl by her elbows as she holds them tightly by her sides or two guys carrying a couch, in neither case are the guys supporting the total weight let alone more than the total weight. Now if the gal were wriggling that's different. As the hanger shifts to find the sweet spot or carelessly drops in the hammock I see the need to for the suspension to exceed the weight of the hanger,but by how much.

Why not hang from Zing it or Fling it, a 2.2 mm is rated at 580#'s & 650#'s average weight respectively.

Why not hang from Dynaglide which a 2 mm line is rated at 1000#'s?

Has anyone hung thru an inline scale and measured the forces transmitted thru hammock suspension. In particular an SLS suspension?

**Dblcorona** · 06-18-2012, 12:18

Good number of guys are using Dyna whoopies. As far as the strap, one of the issues is not weight capacity for you, but how are you putting the weight on the tree. The straps spread the forces so we don't damage the tree. A thin string will damage the tree faster under load.

**gmcttr** · 06-18-2012, 12:31

Originally Posted by dirtwheels

Newbie questions here! From the outside looking in it would seem that the weight supported by the tree straps would be roughly 1/2 of the weight of the hanger and suspension....

If the weight was suspended straight down as in your examples, you would be correct in thinking it would be divided in half.

However, the direction of pull is on an angle for hammock suspensions and the laws of physics take over. The farther the angle is from perpendicular to the ground, the greater the forces become acting on the suspension and trees. Take the same girl and have her lay flat on the ground. Have the two guys pick her up by her hands and feet and see how hard they have to pull to keep her flat rather than "sagging".

Here's a little toy to illustrate how these forces multiply. Move the "weight" with your cursor to see the effects. There are also several charts that have been posted...hopefully someone will provide a link.

**Boothill** · 06-18-2012, 12:43

this might help

http://www.hammockforums.net/gallery...l_original.jpg

boot

**dirtwheels** · 06-18-2012, 12:48

Originally Posted by Dblcorona

Good number of guys are using Dyna whoopies. As far as the strap, one of the issues is not weight capacity for you, but how are you putting the weight on the tree. The straps spread the forces so we don't damage the tree. A thin string will damage the tree faster under load.

I plan to use this:

http://www.rei.com/product/737298/bl...ubular-webbing

Unless there is a good reason to buy straps and cut hooks or buckles off. 10' @ 128 grams/4.5 oz. per side doesn't seem too bad but I haven't seen the weight of the Home Depot tie down straps so it's a guess. I plan to sew a loop on one or both sides. Not sure what length I should use either which is why I'm thinking about starting with 10' can't imagine needing more.

**gmcttr** · 06-18-2012, 12:52

With a ~4000 lbs rating, that's a long way from zing-it. If that webbing is made from nylon rather then polyester, you may experience some stretching. Then again, at 4000#, maybe not.

**Ramblinrev** · 06-18-2012, 13:00

Tubular webbing is made for climbing. It is often intended for dynamic loads, meaning a stretch factor is built in to absorb shock in the event of a catastrophic fall. That is an essential safety feature for climbing, but it can be a detriment for hammocking where the safety factors need not be so robust. The stretch can leave you with your butt on the ground. Generally materials designed for static loads are more than sufficient, given the proper tensile strength.

**dirtwheels** · 06-18-2012, 13:02

Originally Posted by gmcttr

If the weight was suspended straight down as in your examples, you would be correct in thinking it would be divided in half.

However, the direction of pull is on an angle for hammock suspensions and the laws of physics take over. The farther the angle is from perpendicular to the ground, the greater the forces become acting on the suspension and trees. Take the same girl and have her lay flat on the ground. Have the two guys pick her up by her hands and feet and see how hard they have to pull to keep her flat rather than "sagging".

Here's a little toy to illustrate how these forces multiply. Move the "weight" with your cursor to see the effects. There are also several charts that have been posted...hopefully someone will provide a link.

Not to be argumentative, but it that is accurate the force on the shoulders of 2 guys carrying a 200 pound guy in a gurney would be about 400 #'s that seems high. Too bad you can't change the angle! Given your linked tool it would seem that an SLS would be a much more efficient way to hang a hammock. By that I mean one could use rope rated to carry less weight.

I think I have a project to try this in a scaled model using a fishing scale to make measurements.

**Ramblinrev** · 06-18-2012, 13:07

Originally Posted by dirtwheels

Too bad you can't change the angle! Given your linked tool it would seem that an SLS would be a much more efficient way to hang a hammock.

The linked tool does allow you to change the angle. Slide the weight up and down with the cursor. I don't know the physics cause I'm not a mathlete but I have had my supports bend when strung tightly and not bend when I hang loose. All other factors are the same. That says to me the closer you get to horizontal the more stress is placed on the supports. That is consistent with the models presented.