SWAY
SUMMER 2018

two people hanging in a hammock across a forest stream

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Hammocking and Trees

Covers techniques, gear, and impact on ecosystems to understand and build a workable user model.
 

IN THIS SECTION

How to Hang a Hammock

The general expectation around hammocking is that it is an easy and leisurely activity. After all, how hard can it be to tie a net between two trees and lay in it? Well, if you know anything about leading questions...

Just about every hammock hanging guide has a variation on how to hang a hammock, many specific to brands and suspension types. Most use a range of measurements to help users visualize the spatial relationship between hammock and trees, using relational phrases like, “between 10-12 feet”, “walk 5 meters from tree”, “hang at head height”, or my personal favorite, "the hammock should look like a smile suspended between trees".

 
HAMMOCKING GEAR

What is needed to hang a hammock can fit inside a backpack, and gear can be added or removed based on a person's preference. Hammock and straps are essential. After that, ridgelines [note]https://www.hammockforums.net/forum/showthread.php/87094-What-is-a-ridgeline[/note] and underquilts [note]https://www.youtube.com/watch?v=BRMg_USAGtE[/note] are recommended.

Ridgelines help balance the tension and slack on a hammock, while underquilts are like sleeping bags for the outside of a hammock. Hammock campers add further gear to their pack, including tarps and bug nets.

  • Hammock
  • Hammock straps
  • Ridgeline (to alleviate tension and create slack)
  • Underquilt (for colder weather)

hang angle

Hammock Physics

Digging deeper into hammock hanging, you find a small universe of applied physics and engineering, calculating for distance, tension and body weight, to determine optimum position to hang a hammock [note] https://theultimatehang.com/hammock-hang-calculator/ [/note].

Experienced hammockers generally agree on a few factors that improve the comfort of being in a hammock:

  • Hang angle at 30º
  • Body angle 15º off hammock center
  • Ridgeline
  • Underquilt


DEFINING THE HANG ANGLE

The slope at which a hammock sits between two hang points determines the hang angle. When hung at 30º the tension pulling against the tree is roughly equal to the base weight in the hammock.

hangle@2x

Changing the angle

Changing the Angle

The tension from the base weight applied to the hammock is pulling both horizontally and vertically, and this causes a multiplying effect on the load that is felt at both hang points. As the force shifts horizontally, against gravity, the tension increases.

At 30º, you can lay at an ergonomically comfortable angle, with little to no tree damage. At 15º and the tension may be strong enough to cause tree damage. You also get the effect of laying in a stiff, misshapen cot.

Hang at 45º and your hammock will fold you up and wrap around you, creating an uncomfortable, claustrophobic cocoon.

tension@2x

Calculating Tension

Calculating Tension

The formula for determining tension is weight/2tan(θ). If base weight is 200 lbs, and the hang angle is at 30º, then the formula looks like 200/2tan(30). Any trig table will give us the sin, cos, and tangent angle variables, so pulling from that, tan(30) is equal to 0.5774, which puts our formula at 200/2(0.5774). Completing the math, the force applied is equal to 173.2 lbs when the base weight is 200 lbs.

When hung at 15º, the force applied is 373.27 lbs, enough to do damage to a tree’s cambium layer.

Calculating Variables

Calculating Variables

In order to keep tension within a safe range we want to determine the strap trajectory from the hammock.

Imagine stretching out a hammock strap to its full length, and raising the strap at a 30º angle to the hammock. Where would that strap intersect with the surrounding trees? This is the strap trajectory, and helps us determine hang range.

Finding strap trajectory means finding the equilibrium between the following variables:

  • hammock length
  • hang angle
  • base weight
  • sit height

Hammock at 10 ft, angle at 30º, sit height at 18 inches, and base weight at 200 lbs will tell us how high on a given tree to hang straps. 

hammockmeasurements@2x

The second calculation is between tree distance, tree circumference, and strap trajectory. This will give us an estimate of the full 3D space a hammock+straps can easily fit within.

The total length of gear is going to be longer than the ideal distance between trees due to variable trunk circumference and hammock sag. For this model, I’m using a tree circumference of 6 feet.

hammockmodel@2x

Hang Range

Hang Range

The diagram above shows a hang point of 11 feet from the ground, the max hang height of our model. Technically correct, but humanly impractical.

The min hang height is calculated at hammock length, which comes to a slightly more reasonable height of 5.8 feet from the ground for a hammock with a base weight of 200 lbs. Between 5.8 and 11 feet, a user can find the best hang height for them based on distance available between trees.

VARIABLE LIST

These are the primary data inputs needed to calculate an accurate hammock spot for a given user.

  • Hammock length
  • Base weight
  • Strap length
  • Sit height
  • Hang angle
  • Tree circumference
  • Distance between trees
NOTE ON VARIABLES

For the purposes of illustrating some concepts, I've used averages of user and environmental data for modeling hammock positions. In any real-world application, all of this information is highly variable. 

  • Hammock length: 10 ft
  • Strap length: 12 ft
  • Body weight: 200 lbs
  • Tree circumference: 6 ft
  • Distance between trees: 18 ft

The Trees

The Trees

For hammockers, trees are both supportive and dangerous. A great hang spot can be within range of a dead tree near collapse, or a hammock can be hung below unstable and cracked branches one gust of wind from falling down. Hammockers can also unintentionally leave their mark on trees, and with equally fatal results.

 
BARK DAMAGE

The primary cause of bark damage from hammockers comes from using too thin a rope at too high a tension. This causes the rope to break into the outer trunk layer. Use thick straps at least 1 inch wide to avoid unnecessary bark damage.

Any wounds that penetrate the bark will damage the cambium layer, a thin layer of vascular tissue, which is vital to movement of water and nutrients within the tree. Once a wound occurs, decay-causing fungi can enter the heartwood and the decay process begins [note] http://www.mortonarb.org/trees-plants/tree-and-plant-advice/horticulture-care/trunk-wounds-and-decay [/note].
 

cambiumlayer@2x

Hazards

Dead Trees and Hazards

You don’t want to hang your hammock on a dead tree or branch, or hang your hammock within 50 feet of a dead tree. Hammockers have many stories about dead trees either collapsing near them or nearly on them, and for experienced hammockers, knowing how to spot dead or decayed trees is a crucial part of their hammock spot selection.


SIGNS OF DECAY AND HAZARDS
  • Hollow cavities in the wood, most notably the trunk
  • Cracked or detached branches overhead
  • Mushrooms growing at base of tree are signs of internal decay of the wood

User Model

Building a User Model

Here’s the place where augmented reality can really show its potential. By collecting user and environmental variables, and calculating the measurements, a model can be created that is tailored to a specific person and their available gear.

Four Users, One Grove

This section shows what happens when people with different requirements come upon the same grove of trees. Constants for this model include sit height (18in) and trunk circumference (6ft). Tree circumference will vary in the wild and can expand or contract the hang range accordingly.

The users for this example are based on persona variations, and a unique model has been created for each of them. Robin and Casey each occupy a hammock, while Asher and Drew share a hammock together. The combined weight of Asher and Drew determines the base weight of their hammock model.

Mapping grove

Mapping the Grove

This is a birds-eye view of the sample grove that Robin, Casey, Asher and Drew come upon. Each circle represents the circumference of a tree trunk. Tree trunks that are too wide or too thin are marked as not available.

This series of photos shows all the potential spots for each unique model, and how they overlap to create a full map of the grove.

WITH HAZARDS

Some trees in the grove are not part of the overall mapping because they are too thin to support a hammock's base weight, too thick for straps to go around, or just an overall hazard to nature, animals and people around them. 

This small variation on the above model shows how hammock spots change based on changing surroundings. Even removing one tree from a calculation can result in a very different mapping.

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surveys, interviews, and observational activities

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Hammocks7 minute read

User Research12 minute read

AR Research10 minute read

Strategy6 minute read

Interactions8 minute read

Participate4 minute read

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