# Max weight/line stress

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• 03-12-2007, 16:42
Sandy B
Max weight/line stress
Not sure where to put this

I just finished a rigging class(navy) and one of the subjects was sling angle stress and the weight effects of a load when the angles are changed.
SO for all who always wanted to know what type/how much of load they are putting on there tree huggers and hammock line, here it is:
ref: NAVFAC P-307
when a sling angle is reduced to 0 degree the stress is increased by a factor of 13
when the angle is at 5 degrees the stress is increased by a factor of 11.49

so if I tighten my hammock to zero degrees and then lay in it, the lines are about 5 degrees. Now take my weight of 200 lbs times the 11.49 and you have
2298lbs ON EACH side.
So, why does the 1400lb line hold????
Answer, It has a built in safety factor, like 6 to 1 And the load(weight) I place on the hammock is slowly added. (don't jump into your hammock)

And for all those who want to tie a knot in your line, This will reduce the line strenght by 50% (the HH Knot is really a bend/lashing and not a Knot)

There is alot more info on this, If any one wants to 'really' know.

Thanks
Sandy B
• 03-12-2007, 16:47
Just Jeff
I doubt your hammock is really at 5 degrees when you're laying in it...probably at least 15-20. But you're right about everything else...that's why I ended up on meh arse when I used 550 cord... :D
• 03-12-2007, 16:53
Sandy B
Just Jeff,
There is a chart for most angles, I only wrote down the 0 and 5 degree, I'll get a copy to post here.
Thanks
Sandy B
• 03-12-2007, 16:57
blackbishop351
Quote:

Originally Posted by Just Jeff
I doubt your hammock is really at 5 degrees when you're laying in it...probably at least 15-20. But you're right about everything else...that's why I ended up on meh arse when I used 550 cord... :D

Yeah mine's probably at about 5* before I get in it - and that's as tight as I can make it (my HH, anyway). Probably at least 20-25* when I'm in it, maybe more.
• 03-12-2007, 23:08
Coffee
Quote:

Originally Posted by Sandy B
Not sure where to put this

I just finished a rigging class(navy) and one of the subjects was sling angle stress and the weight effects of a load when the angles are changed.
SO for all who always wanted to know what type/how much of load they are putting on there tree huggers and hammock line, here it is:
ref: NAVFAC P-307
when a sling angle is reduced to 0 degree the stress is increased by a factor of 13
when the angle is at 5 degrees the stress is increased by a factor of 11.49

so if I tighten my hammock to zero degrees and then lay in it, the lines are about 5 degrees. Now take my weight of 200 lbs times the 11.49 and you have
2298lbs ON EACH side.
So, why does the 1400lb line hold????
Answer, It has a built in safety factor, like 6 to 1 And the load(weight) I place on the hammock is slowly added. (don't jump into your hammock)

And for all those who want to tie a knot in your line, This will reduce the line strenght by 50% (the HH Knot is really a bend/lashing and not a Knot)

There is alot more info on this, If any one wants to 'really' know.

Thanks
Sandy B

I would say they hold because you are putting half your weight on each support, or 100lbs converted to 1144lbs of stress at 0 degrees. Well below the 1400 lbs breaking strength and any safty factor built in.

An interesting point on the knots. I have heard for a long time and in different places that knots reduce rope strength by 50%.

An interesting question would be which lashing can we use in place of the knots in our setups? Also how much do lashing effect the strength of the rope? I am thinking it is some, but how much.

Quote:

Originally Posted by blackbishop351
Yeah mine's probably at about 5* before I get in it - and that's as tight as I can make it (my HH, anyway). Probably at least 20-25* when I'm in it, maybe more.

That's about where I am. No matter how taught I start, I usually end up around 20 degrees.

BTW, I don't usually gentily get in. I just sit in and swing around. You should see what I do to test it for the first hang.;)
• 03-12-2007, 23:18
blackbishop351
Quote:

Originally Posted by hammock engineer
You should see what I do to test it for the first hang.;)

Do I detect a patented 'Superman Entry Method' in the works? :p
• 03-13-2007, 05:58
Sandy B
Hammock Engineer,
Those factors are based with two slings lifting the load. The math is the stress on EACH leg (or side) of a sling. When a load is rasied with the slings at 90 degrees to the load both slings would lift 1/2 the weight, as the angle is changed by 5 degrees the load lifted starts to increase.
I have put a dynometer(sp) on one leg of a sling and this math works, Maybe I'll take my hammock to work and check it out.:)

Sandy B
• 03-13-2007, 06:05
slowhike
Quote:

Originally Posted by hammock engineer
.
An interesting point on the knots. I have heard for a long time and in different places that knots reduce rope strength by 50%.
. .)

from what i read, some knots take away more than others. that would be useful info to look into.
• 03-13-2007, 10:02
Coffee
Quote:

Originally Posted by Sandy B
Hammock Engineer,
Those factors are based with two slings lifting the load. The math is the stress on EACH leg (or side) of a sling. When a load is rasied with the slings at 90 degrees to the load both slings would lift 1/2 the weight, as the angle is changed by 5 degrees the load lifted starts to increase.
I have put a dynometer(sp) on one leg of a sling and this math works, Maybe I'll take my hammock to work and check it out.:)

Sandy B

That's something I would like to see the results from. It would be interesting so see what the real world data is at different angles. I know and trust the math behind it, but I always like physical data better.
• 03-13-2007, 12:09
lvleph
Quote:

Originally Posted by hammock engineer
That's something I would like to see the results from. It would be interesting so see what the real world data is at different angles. I know and trust the math behind it, but I always like physical data better.

The real world data is almost always different than theoretical. There are almost always losses unaccounted for.
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