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08-06-2008, 19:54   #8
TeeDee
Senior Member

Join Date: Jan 2007
Location: Maryland
Hammock: DIY Bridge
Tarp: DIY 10'x11'
Suspension: Whoopie Slings
Posts: 1,636
Quote:
 Originally Posted by Youngblood I have been experimenting with marking webbing and rope suspension systems to aid in hanging hammocks. Like Grizz mentioned, I use a 31 degree sag angle because the cosine 31 is a convenient ratio of 6/7. I start the marks at a 12 foot span. From that 12 foot reference each foot is incremented 7 inches on each end, so that works out pretty well. What I mark is the span distance because I really don't care about the actual length of the suspension, I just want to know where to tie it off and the distance I do know is the span.
Yes - knowing the span distance makes everything else just fall into place quite neatly.

Using the 7" marking means that you have other means of measuring span distance accurately. How do you accomplish that?

Quote:
 Originally Posted by Youngblood I am of the opinion that if there is one key parameter to get right in hanging a hammock, it is the height to tie off the hammock for the span you are using. If you get that right and are using a low stretch suspension system, about all you have left to worry about is centering the hammock between the span. Get that wrong and everything is more difficult. So my priority list is: 1- Span distance. 2- Tie off height. 3- Height hammock is above ground. 4- Centering hammock.
Yes the span distance is key to the whole thing. That was why I concentrated on getting the markings on my hang rope to measure the span and why I liked HC4U's idea to mark the suspension line. It just makes it easily possible to measure the span accurately. Getting the span distance accurately is important. The tables I use and the rule of thumb that you and Grizz use already introduce error. Magnifying that with an inaccurate span distance pushes you right back into the old set-up, adjust, adjust, adjust, ..... problem.

Also, your rule of cos(31) ~ 6/7, is usable for a single sag angle. You than have only one thing that you can adjust to achieve your desired hammock height - how high you place the tie off points, i.e., the tree huggers. By limiting yourself this way means that where I go, you would have to pass by a LOT of otherwise suitable hang spots and spots that would be better than the ones you could use. I would guess that on the maintained trails in the US this is probably not a problem though.

I would change your above ordering slightly and swap items 2 and 3. Hammock height is what I want and tie off height follows from hammock height and span distance. With a ridge line, computing the tie off height from hammock height and span distance is a simple trig problem. Without a ridge line, you have a much more flexible problem and have to fall back on the "art" of where to place the tie off on the trees as you do with your "rules of thumb" below.

Of course, if you know what the distance between your hammock whipping is when hung, then you know the "virtual" ridge line length and can use that as Grizz mentioned. You then have the problem of accurately measuring span distance. The hang rope with built-in ridge line solves that problem as does my Leica optical rangefinder.

I really think that I would change your list even more in that items 3 and 4 are not items that are unknown, but are my final goals in hanging the hammock. I have the following list in my head when hanging the hammock:
1. accurate span distance measurement
2. sag angle and,
3. tie off point height

I can measure 1, and then mentally adjust 2 and 3 to get my desired/known hammock height. Centering the hammock then follows from sag angle and knowing the measured amount of slack to allow and using the marks on the suspension to accomplish that.

Quote:
 Originally Posted by Youngblood With a marked suspension system, centering of the hammock is hard to mess up. For a tie off height for most hammocks, I suggest shoulder height for a 12 foot span, head high for a 15 foot span, and as high as I can reach for an 18 foot span. (The tie off height is different for some of the larger Hennessy Hammocks. They should be tied higher by a half foot or more.)
Agreed - with the suspension marked, once you know the span distance, you can easily use the marked suspension to get the sag angle at the trees that you want/need. This is easier with a ridge line, but as Grizz pointed out for those that don't like ridge lines, it can still be done. You just have to know what the ridge line length would be if one was there.

Quote:
 Originally Posted by Youngblood I observe the height the hammock is above the ground and use that as the fine and final adjustment to make up for the inaccuracy I sometimes get in determining the span (by pacing or using my outstretched hiking poles. It just happens that I actually 'calibrated' my outstretched hiking poles the other day and found they are more like 13 feet instead of the 'old 12 foot rule' for me.) My fine adjustment is usually adding or subtracting some suspension but occasionally may be the tie off height, it just depends on how things look and feel.
I agree with you that the real key to hanging the hammock easily is getting the span distance. Once you have an accurate measure of that the rest falls easily into place with a marked suspension.

That's the reason I might be carrying that Leica optical rangefinder in the future and will certainly be doing testing with it in the days to follow.

Knowing the span distance accurately immediately with the rangefinder without even having to put the tree huggers on the trees, means that I immediately know several things:
1. if a 30 degree sag angle will be workable
2. what sag angle I can use
3. how high to place the tie off, i.e., how high to place the tree huggers

All of that falls out immediately from the span distance since I already know how high my hammock will be and the fact that I want it to be centered.