love this calculator. hopeing that you will make an android ver. been having trouble figureing out my ridgelne length but this gave me a good place to start tyvm
Love it! Even bought your book! Would love an Android app.
Hej, there is an error in the JS code of this calculator. When I’m using the metric mode, none of the forces are displayed/updated. In the file hammock-hang-calculator.html in line 170 and line 171 the forces for tension and shear are expressed as variables, but they are implemented as function. The expression for the weight force in line 172 seems to be correct but isn’t executed because of the prior error.
Otherwise neat and easy to understand calculator. My first hammock has been shipped yesterday and I’m excited to try it out.
Thanks! I’ve fixed the code and it looks like it is working correctly now.
I bought your app and I got a question on a hennessey asym hammock isn’t the ridge line and hammock the same size? When I put in 15ft distance between anchors, Ridgeline and hammock length 100, preferred sit height 18, weight in hammock 170 lbs, thehang point says 41.1 inches. That is very low! If I put nothing for hammock length or ridgeline the hang point says NaN in?? Please advise
No, the ridgeline is not the same as the size of the hammock. The ridgeline is going to be shorter than your hammock. My Hennessy is only 9.5 ft long when laid down flat, but you’d have to detach the ridgeline in order to pull it out flat. The ridgeline is the cord that runs inside the bug net on the top where the pocket organizer lives. The ridgeline keeps the hammock in a curved shape.
Leave a number, even if zero (0) so the app doesn’t kick back a non-number error (NaN).
Love the calculator. Hope you make a android version. Android people hammock too.
I know, I know I’m looking for a developer. It’s not for lack of desire, but lack of funding.
Is the shear force total or per side? This is a very handy calculator. I’m trying to figure out how to effectively hang my hammock in my US style home, without risking a drop from any height.
I think what makes this confusing is the physics. There are a few forces at work here. First is the weight, or the vertical force. If you weigh 100 units, than each side would share 50 units of vertical force. If the ropes hung down at 90-degrees (straight down), the only force would be vertical. But there is also horizontal force, based on the angle of the hang. The calculator adds the horizontal force based on the angle, so each side will add up to more than half the weight that is in the hammock.
Half the occupant weight + horizontal force = total force on each side.
At 30-degrees, the horizontal force is half of the weight. Again, if the weight is 100:
50 (50% of occupant weight) + 50 (horz. force) = 100 units of force applied to _each_ side.
When you decrease the degree of the hang, you increase the horizontal force. Each side is still sharing an equal amount of vertical force, but they will _increase_ the horizontal force, meaning each side could bear _more_ force than what is being held in the hammock. This throws some folks off because it doesn’t seem to make sense that if I weigh 100 units, each side of the hammock suspension is also bearing 100 units. If you think in terms of “force” instead of “weight” it makes more sense (at least it does to me). It’s not that you magically star weighing _twice_ as much, but the forces are increasing.
In theory, a hammock strung perfectly horizontal (0-degree hang), the horizontal force would be infinite. This is why I encourage folks to hang their hammock at an angle.
Here’s where I’m confused… if the shear force is 300 units do I need two hooks that support 150 units each or two hooks that support 300 units each. I would hate for the hooks to fail and drop me 18 inches…plus I tend to wiggle/swing in my hammock. Falling is so not on my list of things to do. Especially unexpectedly while asleep. OW!
Was much easier in Mexico where the hooks are part of the cement wall and the hooks failing seems rather impossible!
I do appreciate your attempt to explain the physics to me and while I can grasp them theoretically, I’m just not wrapping my head around it completely. I would have probably just bought 2 hooks rated at 250 lbs and assumed I was okay, but then throwing the physics in… Argh! I haven’t had a reason to do physics for about 20 years… lol
Ha! I’m not good at physics either; I just spent a night in a Holiday Inn Express Seriously, I’ve had some help understanding this myself and I often have to refer to my notes to make sure I have it right.
What you are looking for in gear is “safe working load.” When hammocks are rated, for example, they take the breaking strength and then reduce that by a factor to get the safe working load. For example, a hammock with a weight limit of 400 lbs will likely have a breaking strength of 1,600 lbs. This is important because they consider the dynamic aspect of hammocks, just like climbing gear: as you move about in a hammock, you exert different amounts of force. This buffer gives a safe margin of error.
You typically want a safe working load of 4:1 or 5:1 or some go as far as 10:1. A 10:1 ratio is more common with more critical activities such as mountain climbing or hauling freight.
A hammock with a 4:1 safe working load factor that is rated at 250 lbs has a breaking strength of 1,000 lbs. This is sufficient for the type of activity in a hammock.
If the force is 300 lbs, you’ll want a minimum safe working load of 4:1, so you’ll want each component of your hammock system (hooks, ropes, hammock, etc.) to be safety rated above 300 lbs. It’s important to understand the difference between safe working load and breaking strength. Some suspension items, like webbing or rope, is often rated at breaking strength, so you’ll need to calculate and reduce them down to make sure they meet or exceed 300 lbs. If the hardware or soft good you purchase is “safety rated” at 300 lbs, than you should be fine. Manufacturers are required to list the ratio they used on the gear.
For inside my home, I purchased some 3/8 in steel eye bolts. They had a safety rating of 325 lbs and they’ve been working great!
Does this help?
That helps a lot. I’m dealing with an older Mayan string hammock, which I love and have no concerns over a sudden failure there. My only concern was with the bolts going into the stud. I could not imagine that I could unexpectedly break a steel hook (would expect signs of stress to show before failure) BUT when it comes to suspending myself from the wall, I’d prefer not to be stupid.