ridge line length vs hangle

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Scott
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ridge line length vs hangle

#1

Post by Scott » Tue May 31, 2016 12:16 pm

I have read other posts on this, but was hoping for some insight from the more experienced in hammock history...

30 degree angle
83% ridge line length

Those to do not add up. Using an online geometry calculator, I come up with ~86.5% of hammock length to get the 30% angle.

I am fine with my hang, I am comfy. I find I like the 83% with the steeper angle better. But for new hangers trying to get the two references to line up, is there any history on where the two numbers came from, and why they don't match? did someone pick 30 degrees, someone else pick 83%, and then they got matched up and perpetuated?

I remember spending time when I first was using the ultimate hang calculator trying to get it all to work out, and never could. I finally just went with what I liked, which is the real answer.


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sarge
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Re: ridge line length vs hangle

#2

Post by sarge » Tue May 31, 2016 3:16 pm

As to the 30 Degree Angle, that's a fairly easy answer, and has to do with Vector Forces. Thirty degrees has been calculated as the "angle of repose" where ropes supporting a suspended weight put a stress on the main supports that is equal to the weight.

Papa Smurf provided this diagram when somone asked a similar question on Facebook:

http://www.ropebook.com/themes/ropebook ... -chart.jpg

Derek Hansen's Hang Calculator might help too:

http://theultimatehang.com/hammock-hang-calculator/

The 83% thing is a bit of a mystery to me too, but I beleive it has to do with the geometry of the arc that the hammock describes between the two suspension points relative to the chord described by the ridgeline. Its not a hard and fast rule, just a place to start from.
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Re: ridge line length vs hangle

#3

Post by Mophead » Tue May 31, 2016 6:52 pm

FWIW the angle is no longer thirty degrees once you are in the hammock. It sags and may be closer to 45* than 30* once your weight is on it. Not sure what it is exactly because I cant get a look at the hammock while I am in it and dont have any hammock nerds nearby. I dont think this matches any better with the 83.3% though.

When I first started I never heard of the rule. I just experimented with structural and non- structural ridgelines. Ended up with one darn close to 82%. So, I am inclined to think it was probably just something was empirically tested and maybe then a group found out they all were about the same percentage, rounded it to 5/6ths the length so it sounds nice, and recommend it as a starting point.

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Re: ridge line length vs hangle

#4

Post by Scott » Tue May 31, 2016 9:13 pm

just hanging with no weight, at the 82% ridge line, it is almost 50 degrees at the end of the hammock, and gradually sloping less as you get to the center, at some point dropping to 30, then 0, then goes back up. a steeper angle is actually better in some ways since the stress on the suspension drops even more.

I do understand they are both guidelines. In the beginning I was just frustrated I couldn't find 30*. I think the 83% works well.

As for the hang calculator, I even tried marking my suspension at inch lengths to make it easier, still didnt fit quite right. Now I eyeball it, and go.

this came up in my mind as I was measuring and resetting anchor points in my extra room. The wife and daughter are heading out for a long visit out of state, my son and I will 'camp' in the office with a window AC, computer for netflex/vidangel, and shut down the rest of the house for the summer.
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Re: ridge line length vs hangle

#5

Post by Idaho Hanger » Fri Jun 03, 2016 6:11 pm

My guess is that the 30 degree mark comes from the tension calculations. At thirty degrees your tension on each suspension line is exactly double your weight, not counting dynamic forces. Probably just good round numbers to work with. When I first started getting into hammocks I was a bit surprised at 30. In the rigging world you try to keep things at 90-60, no more than 45 EVER because of the increases in tension. This is also the reason I won't rate a hammock at over 300lbs capacity without upgrading the webbing and Amsteel. I'm trying to maintain a 5:1 safety ratio between load and breaking point to account for wear and tear and dynamic forces.

As for the 83%, I'm guessing Sarge is right with the geometry of the arc. All I know is that I've played around with adjustable ridgelines a lot and I found that to be a very good starting point. I never found the need to go more than an inch or two off that number.
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