Strength of rigging parts

[TonyF]

So if I were to make up a ring buckle suspension system, I would need to use two climbing rated rings at both ends? I stopped by Home Depot and they had steel rings, but they were only rated to 200 lbs each. If a 22o lbs person was in a hammock and the angles were going against you, the tension could get up to perhaps 700 lbs at each end?

[TeeDee]

The successive re-tightening makes it hard to figure how much tension you can put on things but it can get pretty high if you get carried away with it. That is the whole point of the hang 'em high campaign. If you hang 'em high you don't need to do that but if you hang them low for a specific span distance and have the easy to adjust suspension length ring buckles, cinches, etc that are close to the hammock knots-- the temptation is there to just re-tighten to get the hammock at the height you want. If you have to go all the way to the tree to make an adjustment and it is just as easy to raise the tie-off height, then there is a better chance of someone raising the tie off height instead of just re-tightening to raise the hammock height.

Not hard at all -it's really very simple and easy to figure the tension. Simply go to any Harbor Freight store and purchase for approximately $6.00 an inclinometer. Using the inclinometer, you can simply measure the angle of the suspension with the horizontal and from the angle and the occupied weight of the hammock compute the tension. You have posted the equations, so I know that you are capable of doing this.

It is true that the angle will tell you the forces that are on the weighted suspension at that instant. It won't tell you the forces that might have been on it before that instant-- the forces that caused something to give, stretch, or reposition to relieve what might have been a higher force when you started with a near-zero suspension sag angle.

It isn't difficult to go through the geometry and force calculations to see how much stretch and drop you get for particular sag angles when you started from a near-zero sag angle (this assumes it is all stretch of the suspension line), I have done that before. For instance, for a HH ULB at a 12 foot span, all it takes is 0.8 inch stretch on each suspension line to get the hammock to drop 5.5 inches and you end up with a 14.5 degree suspension angle that represents 2x the users weight on each suspension line. At a 20 foot span, it takes a 2.4 inch stretch on each suspension line to get an 18 inch drop with that 14.4 degree suspension sag angle.

I would think this is more of an issue with longer spans because the repositioning aspect of the suspension attachment at the trees becomes less of a factor. It is reasonable to expect that certain attachment methods at the trees might limit the minimum suspension sag angle more than other attachment methods. When you have webbing with carabiners, multi-wrap technique, webbing passing through webbing loop and suspension rope attached to only one of the webbing loops, tree huggers where the suspension rope attaches to both webbing loops, a non-cinching loop with a slippery bow line knot, etc, you have a wide variety of attachment methods and they may not all perform the same way where this issue is concerned.

I think to say that 20 deg is not possible is foolish if it is interpreted as an absolute statement and you really mean that is your best guess based on what you have noticed. Someone can always re-tighten things and do it in a 'manly' way. I don't think we know what the limit is. Folks can use a truckers hitch to gain mechanical advantage or other means to get who knows how much force on the suspension lines.

Re-tightening repeatedly to take out looseness after it has stretched can get a little scary when you talk about possible failures just by the very nature of why things might be stretching-- that is almost like a ratcheting effect to slowly raise the hammock. With some of the suspension lines, stretching is what it does before it fails and if you keep re-tightening and causing it to stretch more and more, well even though I did that in the past before I realized what was going on with forces and got by with it, it doesn't sound good to me. People need to be careful in what they do and how they go about adjusting their hammock setups.

You are missing a vital point in what you are writing. The forces present before the stretching and sag are those of the un-occupied hammock which are probably less than 2 lbs. Using 2.8 mm Spyderline rated at 1200 lbsf, for the suspension rope, the angle of the unoccupied hammock would have to be less than 0.05 degrees to equal the Spyderline rating. Maybe the Governor of CA at his physical peak could have pulled the suspension line that tight, but I seriously doubt that most weekend hammock hangers could - well maybe Neo now that he is in training.

So whatever angle the hanger pulls the suspension to before the hammock is occupied is undoubtedly of theoretical interest, but the only angle of real interest is the angle after the hammock is occupied. And, yes it is really a trivial exercise to compute the amount of sag necessary to obtain a given occupied angle, but the exercise does very little to enlighten people.

Instead your time would be better spent investing in an inclinometer and trying to obtain some small sag angles with occupied hammocks.

I have done this. Using a suspension method I used previously which yields a minimum of a 3:1 mechanical advantage, the smallest angle I could obtain for an occupied hammock - occupant weight of 180 lbs - was 18 degrees. To obtain that angle, I had to pull the suspension rope as hard as possible with that 3:1 mechanical advantage. I increased the mechanical advantage to 5:1 and was able to obtain about 15 degrees. This was done with the following ropes for the suspension: 2.8 mm Spyderline, 3 mm Lash-it Dyneema, 3 mm AS-78 dyneema rope and 3 mm Amsteel. All very low stretch ropes. All tests were done with a tree span of approximately 16 ft +/- 3". Now some people may not consider me "manly", but I modestly report that I do 200 pushups during my morning exercises and 18 pullups. So I consider myself capable of exerting some little force in pulling the suspension rope.

After doing the above tests I simply stopped being concerned about braking dyneema suspension ropes and dyneema ridge lines since I am very conservative in the type of knots I use in them.

Now if you are willing to leave the theoretical studies and actually do some field experiments measuring the sag angle you can attain for an occupied hammock, maybe you could stop worrying about excessively small sag angles also. I have noticed that this is a favorite topic of yours and you have posted the equations more than once. However, I have not seen the results of any actual field experiments you may have conducted to obtain and test the small angles you are so concerned about. I learned very early in my many years of formal training and studies in Physics that experiment trumps theory every time. Theory is fine to help explain experimental results, but the experimental results are vital to understanding the theory and guiding one in the use of the theory, especially the use.

Now having written the above, I do not mean it to be an endorsement of trying to obtain the smallest sag angle possible when hanging a hammock. There are valid reasons for not doing so, damage to the trees being probably the most important. There are means available to reduce the possible damage as much as possible, the best being the use of tree huggers of a sufficient width, 1.5" width being my current favorite. However, I also know that there are times that obtaining a sag angle on the order of 20 degrees to 25 degrees is essential also - notably when I am forced to a tree span equal to or greater than about 19'. When I get out to about 20', 21' or 22', I want the smallest sag angle possible since I do not carry a ladder with me in order to hang sufficiently high enough so that the hammock isn't a ground bivy. With large tree spans, small sag angle and a ridge line become essential for me in order to hang and stay off the ground.

So my recommendation isn't to avoid small sag angles at all costs, but to be cognizant of what you are doing and use the sag angle appropriate for the situation.

[warbonnetguy]

teedee, you got to 18deg for an occupied hammock with a 3:1? that's lower than i thought possible

i'm still gonna try cinch buckles and re-tightening.

that do-hickey sounds like something i'll be buying sometime soon. so it reads the angle off horizontal? did you have to make sure the rl was true horizontal before weighting the hammock? seems like the result could get thrown off if it wasn't.

dave,
the yates site does say: "Screamers are very useful in documenting maximum loads in a given situation"

it is nylon, pretty sure it's their 11/16" which is around 2500#. those things look to be 6 layers thick, so that's equivalent to around 15,000#nylon webbing as far as stretch characteristics go, and it's only 6" long. i'd guess it would stretch only a tiny fraction of what the rest of the much longer suspension would be stretching. 6 layers of 2500# nylon should stretch less than 1 layer of 2000# polyester, certainly no more. i mean you're going to get some stretch from the polyester webbing around the trees, probably alot more than the un-activated screamer. you're going to have some stretch in the suspension no matter what you use, i don't think the screamer would add any signifigant amount.

[warbonnetguy]

teedee, when you got 18deg with a 3:1 what were you using for tree straps, polyester? and amsteel for the line? just asking because i used a trucker's hitch and couldn't get near that, i'm trying to figure out why i didn't get it as tight.

[warbonnetguy]

So if I were to make up a ring buckle suspension system, I would need to use two climbing rated rings at both ends? I stopped by Home Depot and they had steel rings, but they were only rated to 200 lbs each. If a 22o lbs person was in a hammock and the angles were going against you, the tension could get up to perhaps 700 lbs at each end?

hardware store rings are no good, or the weld is no good rather, that's the reason for the low rating. you want something with a good butt weld or forged aluminum rap rings, but not the new omega pacific rap rings, they're too fat and won't work i don't think.

[Ramblinrev]

National Hardware (that's the brand) welded rings are rated for 300 # SWL if I remember correctly. They are readily accessible at the local hardware stores. I used the Lowes rings until I found the National Hardware brand. You need to be comfortable with what you use. But by all means hang your own hammock.

[warbonnetguy]

i've broken the weld on hardware store rings before, not sure the brand.

[Ramblinrev]

i've broken the weld on hardware store rings before, not sure the brand.

I am not disputing that. All _I_ am saying is these have worked for _me_. Would I rather have the SMC rings... yes and I am moving slowly to change over to them. I wouldn't anything brand of steel welded rings except the National Hardware. But that's me. YMMV.

[Rushthezeppelin]

i've broken the weld on hardware store rings before, not sure the brand.

Any good sign to watch for before the weld break? I'm using some from Home Depot that are rated 200 lbs atm. I only weigh 135 lbs atm though (I'm short) so maybe it wouldn't work for the majority of people and I'm just lucky to be a tiny guy.

[Youngblood]

...
I have done this. Using a suspension method I used previously which yields a minimum of a 3:1 mechanical advantage, the smallest angle I could obtain for an occupied hammock - occupant weight of 180 lbs - was 18 degrees. To obtain that angle, I had to pull the suspension rope as hard as possible with that 3:1 mechanical advantage. I increased the mechanical advantage to 5:1 and was able to obtain about 15 degrees. This was done with the following ropes for the suspension: 2.8 mm Spyderline, 3 mm Lash-it Dyneema, 3 mm AS-78 dyneema rope and 3 mm Amsteel. All very low stretch ropes. All tests were done with a tree span of approximately 16 ft +/- 3". ...

Did you get out and re-tighten the suspension after occupying the hammock to take out all the stretch you could and repeat that cycle until you could not take out anymore stretch before you measured the smallest angle you could obtain? Did the results vary with the different suspension ropes? How were you securing, or tying off, the suspension ropes to keep them under tension?