So I thought to myself if I was going to use TeeDee's method and still reserve the right to have an adjustable ridgeline, why I'd be bothering the guy all the time to make up new tables for me. Or I could bring my HP calculator (with post-fix entry, of course) out on the trail, along with my laser guided optical range finder to nail this suspension length thing cold.
But having survived freshman physics, once, I retained that things can get simpler if you choose the right frame of reference. So I choose origin of my coordinate system to be the point where the suspension cord attaches to the hammock. What I'm clipping out of the system is the height the hammock is above the ground, because that varies to personal preference. So however it is I've figure out what the distance from hammock end to tree ought to be when centered, that's a variable that depends on site selection. Another variable is the attachment point on the tree. Given these two, you can compute what the length of the suspension cord ought to be, and what the angle of inclination is.
With this one table then you can estimate what length of suspension cord to use to attach at a given height on the tree (above the origin), or for a given suspension length what that height will be.
Lurking in the background of course is physics, that angles which are "too shallow" carry too much force on them. So in the table I cooked up, I mark table entries according to whether they correspond to angles greater than 30 degrees, 25-30 degrees, 20-24 degrees, or 15-19 degrees. Shallower than that is bad for your health and those entries are blacked out.
So I think I'll print this out, get it laminated, and put it in my hammock's stuff sack. I've included here in case anyone else can figure out what on earth I'm talking about, and wants to use it too.
- span distance or distance from hammock to tree
- sag angle
- height above ridge line or hammock
- measured slack amount.
I put that into 2 tables:
- table 1 indexed by 1 & 2 with 4 inside the table, and
Code:Slack Amount - sag angle vs. tree separation Ridge Line Length: 114 Tree Separation -> 12 13 14 15 16 17 18 19 20 20 -- 1 1 2 2 3 3 3 4 4 22 -- 1 2 2 3 3 4 4 4 5 24 -- 1 2 3 3 4 4 5 5 6 26 -- 2 2 3 4 4 5 6 6 7 Sag 28 -- 2 3 4 4 5 6 7 8 8 Angle 30 -- 2 3 4 5 6 7 8 9 10 32 -- 3 4 5 6 7 8 9 10 11 34 -- 3 4 6 7 8 9 11 12 13 36 -- 4 5 6 8 9 11 12 13 15 38 -- 4 6 7 9 10 12 14 15 17 40 -- 5 6 8 10 12 14 16 17 19
- table 2 indexed by 1 & 2 with 3 inside the table
Code:Tree Hugger height above ridge line, 6" increments Ridge Line Length: 114 Tree Separation -> 12 13 14 15 16 17 18 19 20 20 -- 1 -- 2 -- -- 3 -- -- 4 22 -- 1 -- 2 -- 3 -- -- 4 -- 24 -- 1 2 -- -- 3 -- 4 -- 5 26 -- 1 2 -- 3 -- 4 -- 5 -- 28 -- 1 2 -- 3 -- 4 5 -- 6 Sag 30 -- 1 2 3 -- 4 -- 5 -- 6 Angle 32 -- 2 -- 3 -- 4 5 -- 6 7 34 -- 2 -- 3 4 -- 5 6 -- 7 36 -- 2 3 -- 4 5 -- 6 7 8 38 -- 2 3 4 -- 5 6 7 -- 8 40 -- 2 3 4 5 -- 6 7 8 9
your table is indexed by 1 & 3 with 4 inside the table and color indicating 2.
A different twist on the way you look at the problem.
- you have the distance to the tree in 6" increments. You may not find that accurate enough. 6" increments on one end resolves into 12" increments in span distance. That is pretty coarse. Since you are doing only one end instead of the total span distance, you could reduce the increments to 2" or 3" at the most.
- you have the height above hammock or ridge line in increments of 12". Again you may not find that accurate enough. Again you could reduce the resolution of your table and then use fewer entries in this parameter - see next comment
- You have run the table out to 72" height above ridge line. I think you will find that unless the hammock is spread out on the ground that 72" is far more than you are capable of accomplishing. You could limit the table to 36" for most practical situations. Maybe stretch to 48" if you have really long arms or hang your hammock really low.
- use the "All-Weather Copier Paper" and you don't need the lamination.
Both of the large increments in distance to tree and height above hammock are reflected in the limited sag angles you have to choose from. As expected, the higher above the ridge line or hammock the better the sag angle resolution.
You removed the ridge line length from the equation by looking at only one end of the suspension. To do that with my single line suspension I would have an extra step to subtract the ridge line length from the span and divide by 2 to obtain the distance to the tree. I don't do that and just stay with the span distance throughout.
I think that what you have done by removing the ridge line length, makes the table applicable to all set-ups and makes the operator do more mental arithmetic.
Good in that you have a single table for everybody no matter what the ridge line length.
One last observation or question. You are working solely on one end. How do you measure the total span? Do you measure each end separately? Seems like twice the work.
I dug out the plastic bag that Lowes packages the pins in:
They call them Cotterless Hitch Pins.
Thanks for the pointers on hardware at Lowes. Finding stuff at these places is just about as hard as finding things in my gear pile.
r.e. span, I'd measure the total span using my low tech Home Depot range finder, convert to binary, and do a right shift to get the span at one end.
Given that for a year and half I been hanging without benefit of range finders or trig tables and many many people have been hanging for longer also without benefit of the same, my gut instinct is that the resolution "needed" on all this is pretty gross. But my gut instinct is often wrong, and so the question I'd pose is to define what precisely is the attribute which imprecise measurements deleteriously affect.
a) number of inches off-center the hammock hangs
b) number of inches difference between the height of one end of the hammock than another
c) number of inches from the ground the point where the hammock suspension meets the hammock.
d) angle of inclination of the suspension rope.
Are there others?
So for impact of errors...if I'm careful to use the same length at both ends, and careful that the tree attachments are at the same height (I do actually have and carry a very small level that hangs from a line), then I'll get a centered hammock. That should pretty much take care of a) and b).
As for c), if I pay this close attention to centering, I could be off on the height the hammock hangs due to errors in the suspension length, so that one is worth looking more closely at. As for inclination, it really doesn't matter what the inclination is, so long as it isn't too flat. I could estimate it at 32 degrees and have it be 27 degrees, but that doesn't impact safety, which is the key thing.
Is there another metric whose accuracy ought to be looked at? Just for fun I think I'll work up a sensitivity analysis of the hammock height as a function of these measured variables.
slow day at the office
AAAARRRRGGGGG!!!! Reverse Polish input, the most aptly named way to type gibberish into a #$%@ calculator I ever ran into.
I survived exactly 1 semester of Freshman physics, and ran screaming from university.
Came in late to this. What happened to just using 12' of webbing with the ring buckles? Or is this bridge hammock specific, which has always been beyond my feeble mind's ability to fathom...
Bad spellers of the world Untie!
Went retro and returned to cord and webbing only for tree huggers.
Webbing is much heavier than the new high tech ropes and much bulkier also. So it is more to carry and takes much more room inside or outside your pack. The weight and bulk of webbing drove me back to rope.
I originally started using webbing because of the convenience it offered in easily hanging and centering the hammock as opposed to the Hennessy Lashing. Webbing and buckles made the adjusting easier.
Have since learned that there are ways to use rope other than the old Hennessy lashing and that using rope in a method such as this hang rope method can be easier and quicker than using webbing and buckles.
Even if someone didn't want to use the hang rope method, that person could use something like the Carabiner Hitch method, still be much lighter than webbing and just as easy and convenient.
These methods can be used with any hammock and have the added advantage over webbing in that the manufacturer's suspension need not be changed in any way.
Once I returned to using cord for my suspension, I started my quest for a method of hanging the hammock that reduced and hopefully eliminated all the adjusting of the suspension I was doing in hanging the hammock.
That quest has lead me to the hang rope method being discussed here. The article describing the method is here
I would suggest reading the article quickly to get an overview and then reading Grizz summary description and the rest of the discussion here and then reading the article again. It will make more sense the second time around.
By the way, this is one of the reasons I really like my Bridge Hammocks. In my Safari clone, the distance from the bottom of the hammock to the ridge line is twice that of my Bridge Hammocks. The ridge line is 2" shorter than for my Bridge, but for the Safari, at only 16' span, I was already placing the tree huggers at about 7' and a little more. That Safari is the most comfortable regular hammock I have ever used. The Bridge is just as comfortable and much easier to hang because the distance from the bottom of the hammock to the ridge line is about half that of the Safari. Then considering that the Bridge uses less than 2 sq. yards of material vs 6 2/3 sq yards for the Safari and the weight of that Safari is consi9derably more. If I was car camping, I would probably take the Safari for lounging and the Bridge for sleeping. But maybe not, I get a much better view from the Bridge.
With 10' of tree hugger I can use up to 2.5' diameter trees comfortably. If necessary a little more.
Grizz, I agree that the effect of the individual errors may not seem like much, but they do add up quickly.
In my experience, changing the height of my ridge line by even 2" really affects my comfort in entering/exiting the hammock.
As you noted, you and I and lot of others have been hanging hammocks for a long time without the measuring span and slack amount and tree hugger height.
But then we had both been doing a LOT of fiddling to get the hang just right after hanging the hammock. Well maybe you haven't, but I certainly have. I think that is what drives people to the buckles - making the fiddling as easy and painless as possible.
What the measuring does is reduce that fiddling and even outright eliminates it most of the time.
Hang it - done.
Kind of like cooking or chemistry, a little of this and a little that, a speck of this and a peck of that and pretty soon you end up with something for the trash instead of that sumptuous dish you wanted. In chemistry it can be even more disastrous.
Now exactly how accurate do you have to be? Don't know, but experience led me to get as accurate as I could within reason.