Hammock Suspension Idea

[beep]

(scrambles to keep head around the discussion)

In general response to the dynamic/changing aspects of loading, I notice a distinct difference in the ridge line tension between (a) sitting in the hammock and (b) lying in the hammock. Moving my body mass from sitting to lying works to significantly increase the tension on the ridgeline. I'm hypothesizing this happens because my body serves to stiffen and lengthen the hammock body from a relaxed curve to a straighter shape. The load vectors on the whipped ends change as well.

[pgibson]

In well under 24 hours this thread has a lot of information to process though and see what the comfort affecting factors really are. Perhaps the next step is to built what beep is wanting to try and see how it works for him versus anything else that can be cobbled together. Beep I am up for making one with our rings and chain links for you if you want to test it. PM me your # and we can talk exact dimensions and options to see what cost would be for it and I could have it in the mail by tomorrow afternoon.

[beep]

In well under 24 hours this thread has a lot of information to process though and see what the comfort affecting factors really are. Perhaps the next step is to built what beep is wanting to try and see how it works for him versus anything else that can be cobbled together. Beep I am up for making one with our rings and chain links for you if you want to test it. PM me your # and we can talk exact dimensions and options to see what cost would be for it and I could have it in the mail by tomorrow afternoon.

Thanks, Paul...that's a generous offer. As it turns out, I have a "new" delivery (as of yesterday) of 100 feet of 1/8" Amsteel and another 50 feet or so of 7/64" Amsteel along with 180 feet of 2.2mm Lash-It. (BTW, contininuing THANK YOU to Redden Marine for their HF discount!)

I already have my Traveler rigged with Chain Links, Rings and Whoopie Slings, so all I need to do is swap out the stock ridgeline attached to the whipped ends for a longer one attached to the rings (after a bit of measuring and calculation of the needed length). I can see a bit of backyard/weekend tinkering with photos in my future!!

[pgibson]

Cool let us now how it turns out.

[FarStar]

How did primitive cultures ever master use of the hammock?

[thekalimist]

How did primitive cultures ever master use of the hammock?

[TeeDee]

Not all that inexplicably - this is the type of problem I love to give my freshman physics students.

The tension in the ridgeline is dependent on angle, so if we assume the tension is going to make a difference in the way the hammock "feels", you're just plain not going to be able to avoid this problem altogether.

Let's make a simple physics problem, shall we?



If we model the hammock as a simplified situation, with two weights (the two ends of the hammock) suspended by two lines, and a ridgeline between them, we can capture all the essential physics by looking at half of the problem (the forces on the other side will simply be the mirror).

So, the forces acting on the mass m will be the sum of T1, T2, and the force due to gravity, mg. Furthermore, since the mass is stationary and not accelerating, we know the sum of forces acting on it is zero.

Let's break that down into components. We'll assume up and left is positive, and down and right is negative.

In the horizontal direction:
-T1 sin θ + T2 = 0, or T2 = T1 sin θ

In the vertical direction:
T1 cos θ - mg = 0, or T1 cos θ = mg

Putting it all together, T2 = (mg/cos θ) *sin θ, or T2 = mg tan θ

So, even in this incredibly simplified drawing, the tension in the ridgeline depends on the angle at which the hammock is suspended. Since we've already demonstrated that changing the tension in the ridgeline changes the "feel" of the hammock, no matter what you do to the suspension, the angle at which the hammock is hung will affect its feel.

It will just affect it MUCH LESS than it would without a ridgeline, since without a ridgeline the sag would be determined COMPLETELY by the suspension angle, and not mostly by the ridgeline with a slight variation depending on how tight the ridgeline is.



Now as far as WHY the amount of tension in the ridgeline affects the feel of the lay in the hammock - that's a bit more complicated, and you really have to start thinking about how the hammock fabric lies, and what changing the forces on each end of the hammock will do to the feel of it. That's a much more complicated problem, and I am definitely NOT in the mood to attempt to write up a solution

Yes - this is a very simplified analysis.

Grizz posted a more thorough analysis some years back, but I have been unable to find it. Maybe someone that knows the search options better can find it for those wanting to know more.

Basically there are 2 angles to consider, not just one:

1. the sag angle of the suspension at the tree (which mustardman has considered here. well what is normally considered to be the sag angle is the complement of the angle mustardman uses, but that's just convention and either can be used), and
2. the sag angle of the hammock at the juncture of the suspension, ridge line and hammock.

The second angle determines a lot of the comfort factor of the hammock and the first determines the forces exerted on the tree and suspension itself. Setting the second angle is the reason a ridge line is nomally used. Of course, a ridge line is also handy for keeping bug netting out of your face and for hanging stuff during the night.

[GrizzlyAdams]

Yes - this is a very simplified analysis.

Grizz posted a more thorough analysis some years back, but I have been unable to find it. Maybe someone that knows the search options better can find it for those wanting to know more.

on google: Professor TeeDee site:hammockforums.net

got me to the right thread, and then the posting of which you speak. Thanks for remembering

[Mustardman]

Yes - this is a very simplified analysis.

That was pretty much the point - my only intention was to demonstrate that the suspension angle changes the tension in the ridgeline, and I chose the absolute simplest geometry to illustrate that fact.

It's quite easy to make up a much more complicated model that captures more of the comfort factors, but unlike Grizz, I don't do math involving more than two vectors for free

[FarStar]

I'm trying to install a system like the one beep diagrams at the start of this thread. Chain links and whoopies, with rings permanently affixed to the unadjustable ends, are on. One end of the whoopie for my ridgeline is on, but I'm stumped as to how to attach the other end of the whoopie to the opposite ring. Suggestions?

Thanks.