Tree World - View Single Post - Slings

Tree Machine · 20th August 2007, 09:54 PM

The short length has a lot to do with it, split tail or sling.

I don't think a dynamic sling (or dynamic split tail) would stretch much, given that the length is so short. For instance, a 1 meter long eye-eye sling with a 5% elongation at 100 Kg would stretch 5 cm (~2"). This is on paper. In the actual act, once the sling chokers down, the portion of the sling actually wrapping around the limb would stay (more or less) situated in a static sense, and the portion from the limb to the rigging line would take the 'stretch', making the overall stretch even less. I think this is so minimal as to offer next to nothing in the practical sense of shock absorbtion.

Now, of course, these numbers are anecdotal (not shown in a scientifically objective way whatsoever), but from a purely practical standpoint you would have to ask, what benefit would there be for the sling to stretch (which it does to a small degree anyway)?

I would worry about sewn slings stretching and distorting the stitching.

Research and science can measure, with a dynamometer, the forces exerted on the dynamometer, and those force totals are extrapolated to mean this is the force being placed on the, in our case here, the sling. But, that part of the sling around the limb and through the caribiner is subject to the force of friction as well, and that friction is affected by the diameter of the limb as well as the overall surface contact and the texture of the bark and maybe other factors like if the limb were wet.

From the standpoint of physics, the stretch characteristics of the overall sling can not accurately be measured. Without precise, accurate measurement, objective data can not be scientifically expressed. If it can not be scientifically expressed, anything we have to say is anecdotal.

Not that this is bad or anything, it just is what it is.

Any discussion, therefore, is conjecture. Information in this sense, then becomes empirical.

Some things don't need accurate measurement, just accurate interpretation of what's going on. So much of Arboriculture is just this.

20th August 2007, 09:54 PM	#5 (permalink)
Tree Machine Over mature heritage tree Join Date: Mar 2007 Location: Indianapolis Posts: 714	To what degree....? The short length has a lot to do with it, split tail or sling. I don't think a dynamic sling (or dynamic split tail) would stretch much, given that the length is so short. For instance, a 1 meter long eye-eye sling with a 5% elongation at 100 Kg would stretch 5 cm (~2"). This is on paper. In the actual act, once the sling chokers down, the portion of the sling actually wrapping around the limb would stay (more or less) situated in a static sense, and the portion from the limb to the rigging line would take the 'stretch', making the overall stretch even less. I think this is so minimal as to offer next to nothing in the practical sense of shock absorbtion. Now, of course, these numbers are anecdotal (not shown in a scientifically objective way whatsoever), but from a purely practical standpoint you would have to ask, what benefit would there be for the sling to stretch (which it does to a small degree anyway)? I would worry about sewn slings stretching and distorting the stitching. Research and science can measure, with a dynamometer, the forces exerted on the dynamometer, and those force totals are extrapolated to mean this is the force being placed on the, in our case here, the sling. But, that part of the sling around the limb and through the caribiner is subject to the force of friction as well, and that friction is affected by the diameter of the limb as well as the overall surface contact and the texture of the bark and maybe other factors like if the limb were wet. From the standpoint of physics, the stretch characteristics of the overall sling can not accurately be measured. Without precise, accurate measurement, objective data can not be scientifically expressed. If it can not be scientifically expressed, anything we have to say is anecdotal. Not that this is bad or anything, it just is what it is. Any discussion, therefore, is conjecture. Information in this sense, then becomes empirical. Some things don't need accurate measurement, just accurate interpretation of what's going on. So much of Arboriculture is just this.