Hitchcraft for hammock tensioning

[TeeDee]

TeeDee - I'm afraid I may not have made myself clear. When I say ignore the ridgeline I don't mean that it makes no difference. What I mean is that when you analize the forces you can cut the ridgeline out of the equation. You can look at the forces by looking at the hammock as a black box suspended by two ropes. The only thing that you need to know to calculate the forces on the rope (and rope hardware) is the angle and the load.

Yes, you can replace the hammock by a blackbox, but when you do so, you have to ascribe to the blackbox the properties of the hammock. Assigning zero properties to the ridgeline and saying that the forces are solely determined by the angle of the suspension line is not correct.

SO with or without ridgeline, what matters is the angle of the rope when you are hanging on the hammock.

Incorrect. The ridgeline affects the properties of the hammock and trying to deny that leads to false conclusions.

If you really believe that the ridge line has no affect on the properties of the hammock, then you will have absolutely no hesitation to perform the following experiment:

1. Hang your Hennessy hammock in the way that you like,

2. climb in the hammock,

3. get comfortable,

4. then reach up and with a sharp knife, cut the Hennessy structural ridgeline.

If you are correct, there will zero effect of cutting the ridgeline. If you incorrect, then you will experience the effect of the Hennessy structural ridgeline. Please have your assistant standing by with a video camera and report back the results of your experiment.

[txulrich]

I can see this as an interesting science experiment. Put force guages on the hammock support ropes. Place 50, 100 and 200 lbs. in a hammock w/o a ridgeline and take the readings. Then try another set with an additional force guage inserted with a ridgeline and repeat the measurements. Anybody got access to a physics lab?????

[TeeDee]

I don't want to get too technical but to take this argument to conclusion I have to. By reverse engineering my HH I find that the rope has a breaking load of 1600 lbs. The manufacturer's suggested working load on a rope is 20% of that limit (from Samson Ropes literature). That tells me my hammock was designed for a maximum load of 320 lbs on the rope, which at 30 degrees means a 320 lb weight. That results in a safety factor of 1.28 for the design load of 250lbs. If you reduce the angle the factor of safety goes away. You might want to check with the manufacturer what their recommendation is, but as a product developer this is how I make my assessment.

Trying to analyze the forces on the hammock based on the rope strengths is not a very good method for engineering.

[hitchman]

Please, let's back up TeeDee. I don't think you are understanding me.
Let me follow your example. If I cut the ridgeline the angle of the ropes outside will increase, meaning that the tension on the ropes relaxes. What I stated before is still true. The load on the ropes is a function of the angle. By cutting the ridgeline the angle changed, and so did the tension.
Does this make sense?

[TeeDee]

Please, let's back up TeeDee. I don't think you are understanding me.

I'm understanding you completely - I don't think the reverse is true. You seem to want to totally deny that the ridge line has any effect. I think you are wrong. I don't think we can agree coming from such totally opposite directions.

We can just leave it at that.

[blackbishop351]

TeeDee, either you guys aren't understanding each other or he's got you on this one. I've thought about it some more and drew some diagrams. The forces due to the ridgeline - pre-tension and elasticity - can be ignored by simply measuring the sag angle. Basically, what I think hitchman is saying is that a non-ridgeline hammock with a certain sag angle and load will put the same forces on its suspension as a ridgeline hammock with the same load at the same sag angle. Think about it for a minute.

[hitchman]

Trying to analyze the forces on the hammock based on the rope strengths is not a very good method for engineering.

I am interested in the forces that would be applied to the hitchcraft tie when it is used to tension the rope, outside the ridgeline attachment. From that point of view the only thing that I am trying to obtain from this community is the typical range of the rope angle.
I have put many hundreds of hours developing a product that I think has a good application with hammocks. I want to learn as much from this community as possible to be able to make well grounded recommendations.

[hitchman]

TeeDee, either you guys aren't understanding each other or he's got you on this one. I've thought about it some more and drew some diagrams. The forces due to the ridgeline - pre-tension and elasticity - can be ignored by simply measuring the sag angle. Basically, what I think hitchman is saying is that a non-ridgeline hammock with a certain sag angle and load will put the same forces on its suspension as a ridgeline hammock with the same load at the same sag angle. Think about it for a minute.

Thanks for bringing in some clarity!

[Coffee]

Jumping into the end of the arguement.

I think there are not a lot of forces acting on the ridgeline. Here is my thinking (no data to back it up, just my own observations).

I have been playing around with my DIY hammock a lot lately to get the feel just right. A couple times I made the ridgeline so long that it was too long for the length of the hammock. With me in the hammock, the ridgeline would not stay taught. I was at the upper edges of the ridgelines capability.

On another one I used para cord. This stiff has a lot of stretch. I could never get it taught.

When I hang my hammock at a large angle (approx 30 deg), the ridgeline without me in it is taught but not under a lot of preasure. I think that (just by eye-balling) the hammock and hammock support ropes looked to be pretty inline with the suspension straps. If you were to draw a force diagram of this, it would show the hammock pulling down and the support straps pulling up. With an added force from the ridgeline. The bulk of the force would be from the hammock.

I think that the ridgeline would take a lot more force if it was always hung close to 0 deg. I think this would greatly add to the force on it from the hammock. It would also see the force on it from pulling it taught.

I think the best way to test this would be to use some really low rated line as your ridgeline. See what breaks and what doesn't. I think just by looking at the hh ridgeline you can say tom h already knows this. The ridgeline doesn't look strong enough to hold much force.

I think that in the end if he was greatly underestimating the forces added from the ridgeline, his pulleys thingy's would have broken long ago. But since he reported well over 100 uses, I would have to agree with his real word data.

[Coffee]

TeeDee, either you guys aren't understanding each other or he's got you on this one. I've thought about it some more and drew some diagrams. The forces due to the ridgeline - pre-tension and elasticity - can be ignored by simply measuring the sag angle. Basically, what I think hitchman is saying is that a non-ridgeline hammock with a certain sag angle and load will put the same forces on its suspension as a ridgeline hammock with the same load at the same sag angle. Think about it for a minute.

Crap beaten again.