Whoopie Sling Excel Worksheet

[e_2]

I was going to comment that it should be noted all dimensions are in inches, but noticed the "rope length required" box is in inches (also feet)... so all the other dimensions are probably inches too. Easy enough to convert now-a-days, I guess.

One thing that should really be mentioned is the fact that as soon as you drop down to 1.x or 2.x mm cord thicknesses, you need a longer bury... NOT a shorter one. Friction in the bury is the thing that keep your tarp (or whatever) off the ground.

[H2Oboy007]

One thing that should really be mentioned is the fact that as soon as you drop down to 1.x or 2.x mm cord thicknesses, you need a longer bury... NOT a shorter one. Friction in the bury is the thing that keep your tarp (or whatever) off the ground.

e_2,
That's a really good point. Is there an accepted rule on bury length? I took the math off of the previous worksheet, I build my zing-it whoopies with a 6-8" bury that I account for in the comfort margin box. I have tried one with the minimum bury suggested... but I didn't feel comfortable. If I can find bury recommendations it would be a fairly easy thing to put in as opposed to the formula that is there now.

Thanks

[e_2]

hmmm.... that's a bit more physics than I can do. If a normal 7/64" Amsteel Blue rope is 0.109375 inches (2.778mm) in diameter, the circumference is that x pi... or about 0.3436 in. (8.728mm). Now multiply that with the length of bury you are "comfortable" with (let's say 6 inches or 152.4mm) and you supposedly get the bury's contact surface area (2.062 inches pr 52.37mm) which friction is working on. Now reverse the process for 2mm dyneema cord or 1.7mm... or 1.2mm you will notice that the length of the bury will get longer and longer in order to satisfy the same amount of "friction area" as the 7/64 inch rope.

The problems with this are:
a) actual diameter of the rope under load may be different
b) the rope is not a perfect cylinder - many bumps and fibrous surfaces..
c) the condition, construction and weave of the rope all play a part in this
d) I could be totally wrong, but hey... it's your butt

[H2Oboy007]

That's more physics than I'm willing to do... without a paycheck. Maybe I'll just pull the suggested bury and put an input box that asks for "user desired bury length". I think my 6-8" buries are probably somewhere between good and conservative (at least, they haven't dropped me yet)... but, like I said before, I wasn't really comfortable with the minimum.

I, for one, am not interested in "unexpected vertical transitions".

I'll update this when I get a chance and make those changes.

Thanks for the input.

[ACoffee]

Thanks for this great calculator NomadicPsyche! I downloaded it, and being the engineer that I am, I proceeded to modify the crap out of it for my own use, sorry Anyway, I thought I would re-post it here to share. Let me know if you find the changes I made helpful (...or the opposite).

I changed the "inputs", so I could enter exactly how long I wanted the whoopie sling to be and it would calculate the rest. I also added estimations for the weight capacity (and the total weight) of the whoopie sling made from different materials. However, the amount that the splices derate the strength of the rope and the proper safety factor to use are up for a lot of discussion here on HF, so just enter what you are comfortable with and hang at your own risk. The weights of the ropes themselves are mostly "borrowed" from Dutch's shipping weights (thanks Dutch!), so I can't verify the accuracy, but they should get you in the ballpark and give a decent comparison between materials.

Also, I have no idea what the baseline safety factor for a SRL should be. It shouldn't be supporting much of the weight of the hanger, but how much tension is on the SRL also depends on the hammock size/ridgeline length/suspension angle/etc. Any thoughts here? Has anyone broken a SRL before?

Whoopie Sling v2.xlsx

Google Docs Version:
https://docs.google.com/spreadsheets...it?usp=sharing

[mab0852]

Further modified by another tinkering engineer.

Sling guide calculator.xls