Badly performing whoopie constriction?

[DemostiX]

I recently heavily loaded a whoopie sling made up by one of the veterans here, one made with -- I think -- (bright orange,slick) Dynaglide.

When I went to release the sling, I was surprised to see that all of the constriction seemed to be in the last 1 inch of 6, and that both the inner corps and constrictor remained very, tightly compressed. So tightly that I had to work with a pick a bit to re-balance the tightness of the constrictor. Milking it was not an option.

So, the question is, simple as it is to make the whoopie sling work and work well, is there a wrong way to make it work, with me having done it that it that wrong way?

Or, is this an issue with ultra-slick dyneema-based cord and rope? I am reading Brion Toss's "Knots for Boaters", and he is very sensitive to knots appropriate to particular materials.

[BrianWillan]

Using Dynaglide for a hammock suspension has a recommended weight limit of 200 pounds or so, IIRC. The break strength of dynaglide is 1000 pounds so the angle of hammock suspension is more critical than it is with thicker amsteel.

So when you say you heavily loaded your dynaglide, how many pounds are we talking about? Whoopie slings will fail at the exit of the adjustable bury. So perhaps you were getting close to the failure of dynaglide whoopie sling.

Cheers

Brian

[DemostiX]

Brian:
Well, there is a mechanical advantage of two on the sling, and I leaned and pulled hard on the tail to get a taut line between two trees, one of them a bit flexible, so the line was loaded, but not that much because the restrictor released an inch before grabbing the core. Maybe I should not have used the word "failure". The cord and constrictor both look well worked-in, but the "pre-stressing was concentrated as described. A soft shackle of older, thinner Spectra did not fail.

Ropes comes with different coatings. I wonder whether just as some rope materials take some knots but will not release them -- I just read advice in a rescue-training manual of expecting to cut some knots out of a rope after one use-- that either the tail should not be pulled back 180 degrees against the load, as I did, because that concentrates the restriction, or that the coating lets the braid get too tight with hollow core Dynaglide.

This put out there for discussion. I have no quarrel with the workmanship of the whoopies or anything else I bought from this forum member.

[SlowBro]

Brian:
Well, there is a mechanical advantage of two on the sling, and I leaned and pulled hard on the tail to get a taut line between two trees, one of them a bit flexible, so the line was loaded, but not that much because the restrictor released an inch before grabbing the core. Maybe I should not have used the word "failure". The cord and constrictor both look well worked-in, but the "pre-stressing was concentrated as described. A soft shackle of older, thinner Spectra did not fail.

Ropes comes with different coatings. I wonder whether just as some rope materials take some knots but will not release them -- I just read advice in a rescue-training manual of expecting to cut some knots out of a rope after one use-- that either the tail should not be pulled back 180 degrees against the load, as I did, because that concentrates the restriction, or that the coating lets the braid get too tight with hollow core Dynaglide.

This put out there for discussion. I have no quarrel with the workmanship of the whoopies or anything else I bought from this forum member.

If you were using the whoopie as part of a tarp ridgeline then snugging it up is appropriate but hard to release so I would clip it with a 'biner.
I you were pulling on the whoopie tail to get your hammock "taut" between to trees then I think you were hanging your hammock wrong. Usually you want to have the hammock hang at about 30 degrees from horizontal when you are in it. If you get in a hammock with taut whoopies you will multiply the stress on your lines many times your weight. That could cause the whoopies to bind up. Hanging at 30 degrees minimizes the stress to the suspension. See THIS Illustration
-Mark

[DemostiX]

Thinking on this further, it would be great if an engineer or engineering tech or other person familiar with rope and knots behavior would comment on this. I think the situation here is what goes on when you are making a complex knot, say a turks head stopper, and are instructed to work it tight from the inside out, that it is not adequate to just pull on the tails, because the core of the knot will remain loose, and the knot will eventually fail.

In the case of the whoopie, you would like the constriction over the core to take place over much of the length of the constrictor. But, when I pulled on the tail, several times in a direction opposite the load several times, I concentrated all of the weight -- say 100 lb -- on maybe just 1/200 sq inch " (1 side (= 1/2) X 1/10 x 1/10) of the leading edge of the constrictor. I could dream that the force was being passed up the constrictor. But without my help in distributing some of the energy with the other hand, the strands near the opening just became tighter and tighter.

To be clear here, I think this operator error -- as in not forming up a knot correctly -- or a problem with the material, or both, not a fault whoopie slings or the maker.

[gmcttr]

...But, when I pulled on the tail, several times in a direction opposite the load several times, I concentrated all of the weight -- say 100 lb -- on maybe just 1/200 sq inch " (1 side (= 1/2) X 1/10 x 1/10) of the leading edge of the constrictor. I could dream that the force was being passed up the constrictor...

I'm not sure what you did, but it's sounding like operator error.

In general, you can't release or tighten a whoopie while it is under load.

You also cannot adjust it by only pulling on the tail (on either side of the constrictor.

To shorten it, you hold the end of the constrictor between your thumb and finger so that the constrictor releases as you pull the tail in line with the constrictor.

To lengthen it, you do the same at the other end of the constrictor.

You should now be confused by my attempt to explain it. We need a video.

[gmcttr]

OK...we have video. Thank you Shug. Hammock Hangin' How-To PART 1... Essentials For Noobs Part 1

Starting at about 6:35, Shug shows how to adjust a whoopie sling.

[default]

i think he may have been doing what i didn when i got my suspension originally (not thinking)

when i set up the whoopie/tree strap/crl suspension i tightened the whoopies to the point where the whole shebang was a straight line across the 2 trees and would retighten as needed. i was thinking since my suspension and ARL was basically a straight line and the hammock was constantly at a good angle, id be fine.

i think i was wrong to do that, and it sounds kinda like what the OP was describing.

[gargoyle]

The sling is not meant to be a "mechanical advantage".
It is only meant to allow easy adjustment in length.
Try to maintain the 30* rule. From your treestraps to your hammock, the line will be running downhill.

If your cranking the whoopie and the hammock too tight, it takes away from the strength and the comfort.
If your hang location is wide, raise the straps higher to maintain proper angle and hammock height.

I'm a lot heavier than most, and hang on dynaglide without an issue. I adjust the sling to the appropriate sag and milk the whoopie out before loading. Test the hang and readjust if neccessary.

[DemostiX]

OP here.

This isn't about hanging a hammock. It is about what happened to the cord in one whoopie sling. In fact, I never hung or tried to hang from the whoopie, just to use it to get a tight line between a solid tree and a not-so-thick one.

The operator error is in using the tail pulled back toward the fixed eye to release the constrictor jacket. That isn't gentle, but it does work to tighten the sling. It is, with respect, exactly what most users will do to tighten single and double overhead tarp lines to get the line(s) and tarp taut. It is the same action most users will apply to line-locs too. It happens that when there's a bit of stretch or give somewhere in the system, that the whoopie constictor will or almost will catch and constrict on release of the tail, with very little assistance. Not different than what happens with the Chinese finger trap.

What I described was a severe constricting of a small portion of the constrictor. Further, because the dyneema cord is loose when new, the worked portion, under the restrictor does get tighter and thinner. Among the modifications to rope is exactly such pre-tensioning.

Just as rope and cord of some materials should not be used for certain knots, because knots tend to become permanent, I wondered whether Dynaglide* constrictors might "fail" in the particular way I described -- not break -- when subject to use in this way, maybe because of the coating put on it for its intended purpose.* To ask the questions is no different than asking whether a particular much-favored hitch is not the right one for a particular kind of rope. (For example Brian Toss writes: "The buntline hitch holds admirably in slick synthetics, better than...Two Half Hitches. It is the preferred knot for anything but extreme loads. Try it as a replacement in many circumstances for the weaker, less secure, more space-consuming Bowline." (Knots for Boaters.)

* " pre-stretched and tensile-set then treated with a vinyl coating. Compact design glides easily over branches allowing lighter throw weights."

I am not suggesting that Amsteel Blue will behave in this fashion. I don't know yet whether the 7/64 Spectra on hand will behave in this fashion. Vectran rope was popular for a time in boating use before some undesirable properties had it lose favor. I know little about rope except what I have been recently reading in mfg lit and on nautical and arborist rigging boards. There's lots of kinds of it, because ropes have properties beside tensile strength, weight, and cost.

A big BTW here is that we all like light and strong and thin in rope. Except when we have to handle it, when most of us wouldn't mind if could magically turn into 1/4" or larger. And then shrink back down when we are packing up.