Aug 152018
 

Hammock Research

Hammock with bamboo stand (Hammock Universe)

A few years back, I stayed at my cousin’s house in England. She had a backyard hammock, so I tried it. I was tired (jet lag) and the big hammock was so comfortable that I immediately fell asleep.

Recently, we were given another hammock, about six-feet long with a fold-out frame. I hoped it would transport me to the same ecstasies of comfort. I tried to get into it, but fipped myself onto the grass. After several attempts, I managed to place myself in the middle of the hammock. It was nowhere near as comfortable as the one I’d tried in England. The sides curved, but the lower section was stiff and hard.

This got me curious about hammocks, and I’ve been researching different models, to see if I want to buy one that will Suit My Purposes… whatever those turn out to be.

A hammock seems a simple thing, but buying one and setting it up is more complicated than I realized.

It seems that most hammocks fall into one of two broad categories – those designed for camping, and those designed for use in a backyard. Typically, the camping type are lightweight and designed to be strung between trees, whereas the backyard type are larger and often hung from a heavy stand.

Of course, there’s some overlap here. You could use a camping hammock in the back yard, if you have something to attach it to.

Some camping hammocks

The camping hammock is intended to be carried in a pack, so it has to be strong but light. The better hammocks are made of lightweight ripstop nylon, similar to parachute cloth. Ripstop means that strong threads are woven through the thin fabric. If the fabric is punctured, it will only tear as far as the nearest thread – rather than, say, ripping wide open and letting the unfortunate occupant onto the ground. Of course, you pay extra for the light weight and compact form.

Some campers use the hammock in place of a tent. They climb into the hammock, with a mosquito net enclosing it, and a fly (tentlike sheet) over the top.

There seems to be a consensus that a single hammock is a good choice for backpacking and camping, but that for increased comfort, or backyard use, a double hammock is the way to go.

ENO

Disappointingly, this ENO is unconnected with the avant-garde music producer. It stands for Eagle’s Nest Outfitting, a US outfit. Their double hammock is very popular.

On ENO’s Canadian store, prices are $90 (CAD) for the double hammock, or various fancy print options for $100. Available for less on Amazon. There’s a wide range of colours.

Kammok

I checked various online forums, and people who are snooty about ENO hammocks often prefer Kammok. Kammok appear to be well made and cost a little more than ENO.

Kammok’s standard double hammock is the Roo Double. This comes in seven colours. Selection on Amazon.ca is poor, but Mountain Equipment Co-op carries it for $125 (CAD). They have it in sky blue or orange.

Like many hammocks, the Kammok includes only the hammock itself, with carabiner clips at each end. In the pictures, the clips look like plastic, but they’re actually “aerospace-grade aluminum”.

Hennessy

Another interesting choice is Hennessy hammocks. These are designed as a substitute for a tent, and include a fly (the tent bit) and mosquito mesh and the suspension ropes to hang it up. If you were thinking about buying those add-ons anyway, the Hennessy system is about the same price, and the mesh is permanently fixed to the hammock, rather than having to be strung on afterwards.

The Hennessy comes in two versions. One has a zipper along the side. The other – the “classic” – has a Velcro seam along the bottom through which you climb in. One owner commented that he once set the head of the hammock higher than the foot end. During the night, his body slid forward towards the Velcro gap and the hammock “birthed” him. Let’s all point and laugh. Hahahahaha.

And you’ll need… fasteners…

For most brands, attaching the hammock to anything requires extras. For example, if you want to tie your Kammok to a tree, you’ll need to by a set of their “Python” straps. The Python is a long strap made from two strips of webbing joined together at various points along their length to make what are basically a series of loops. You wrap the strap around a tree, feed it through its own end loop, then fasten the hammock to whichever loop puts the hammock at the correct 30º angle.

Fastening a hammock to a stand usually requires a length of chain. It’s sold as a kit, or you can buy a couple of 2-foot lengths at a hardware store.

And you’ll need… a mosquito net…

For most hammocks, this giant, half-moon of mosquito mesh is an optional extra. It surrounds the hammock, and fastens with zippers and drawstrings, leaving no holes hungry insects can get through. It’s strung up separately, so the mesh stays well above your head. For some brands, this costs as much as the hammock itself. A few camping hammocks have the mosquito net built in.

Backyard hammocks

These hammocks are designed for casual lounging and often come with a frame made of steel or wood. Weight is less of a consideration here.

Some hammocks have spreader bars at one or both ends. This makes the hammock flatter, but also more likely to tip when you get into it. Hammocks without spreader bars take on a banana shape.

My friend Karen swears by this Mayan hammock from Lee Valley. It’s 13 feet long, very durable, and comes in bright colours.

Hammock Universe also sells a similar (possibly identical) hammock. It also comes in a larger family size, which supports over 800 pounds of human biomass.

I found Hammock Universe to be pretty good for backyard hammocks. They have a wide range of styles, ship from Canada, and their hammocks seem to have informative and positive reviews from buyers. (They seem like real reviews, although it’s hard to tell these days.)

Deadly hammock physics

The obvious concern with a hammock is that a rope or fixture might break, sending the hammock and occupant falling to the ground. So, don’t string up a hammock more than 18 inches from the ground, and don’t arrange your spike collection underneath it.

However, the real risk with hammocks is more subtle. When a hammock is mounted on two trees, the pull of gravity on the hammock and its occupant creates a horizontal force on the trees, pulling them inswards. This force is quite low if the hammock is saggy, but if the ropes are made tighter, so they become more horizontal, the inward pull on the ropes and trees quickly becomes very high.

This online calculator shows some figures. (Enter the numbers in the boxes below. The various forces appear in the picture at the top.)

If a 200-pound man (or two 100-pound teenagers, or a sack of 100 two-pound kittens) lies in a hammock at a saggy 45-degree angle, the horizontal force on each rope and each tree is 100 pounds. (There’s also a downward force of 100 pounds on each tree, but that’s less of a concern, for the same reasons that pushing on a tree is more likely to bring it down than climbing it.)

Tighten the ropes a little, so the hammock lies at a 30-degree angle, and the horizontal force increases to just over 173 pounds. This is the angle most people recommend for a hammock. Ropes, hammocks, and healthy, mature trees should be able to deal with this kind of force.

At 20 degrees, the force jumps significantly to 274 pounds.

At 15 degrees (that’s it, get it nice and tight now!) it’s up to 373 pounds. This is getting dangerous.

And if your quest for a flatter hammock leads you to tighten the hammock to a 5-degree angle (that is, 5 degrees from horizontal), when you lie down in it, the force pulling inwards on each rope is 1143 pounds.

At three-degrees, it’s close to a ton.

These are colossal forces, and people don’t have an intuitive grasp of the risks. If you’re lucky, ropes break and you fall. If you’re less lucky, trees or posts break, you fall, and the tree falls in the direction it’s being pulled – right on top of you. There are plenty of reports of hammocks that have toppled trees, posts and brick pillars, all of which come crashing down on their occupants.

People will recommend “good strong rope” – but whatever rope you use, you’re up against the harsh laws of physics. If you want to string a hammock to trees, choose live trees with trunks at least four inches wide, and a rope angle of no more than 30 degrees. If you want to lie more horizontally, whatever you do, don’t be tempted to tighten the ropes, or those horizontal forces will soar. Instead, try lying diagonally. Or buy a bed.

This YouTube video from Inside Edition shows some hammock accidents, and offers some tips, but they miss the point about those potentially huge horizontal forces. The worst accident involved sturdy ropes on a sturdy hammock. It demolished a brick column on the front of a house and paralyzed the occupant.

If you could string the hammock up perfectly horizontally, the force on the supports would be INFINITE. Yes, I said infinite. You could level continents with a hammock.

Remember Alexander the Great slicing the Gordian Knot? That was a hammock knot. Cutting it set Asia adrift. Probably.

Hammock Stands

The easiest way to mount a hammock is between two live, sturdy trees at the correct angle (see above), but trees aren’t always available in a backyard.

Hammock stands provide a relatively safe way of supporting a backyard hammock.

The cheapest options are three-beam stands, comprising a simple arrangement of three straight pieces of coated steel tubing, with a couple of bars fastened sideways to make a base. It looks like a piece of exercise equipment. The angles of the beams distribute the force along the length of the steel tubes, which is a sturdy arrangement. (If you mounted the same beams as posts, a tight hammock would easily bend or snap them.)

I find it slightly offputting to know that, if the hammock were to fall, my back would land right on the steel bar below. But hopefully this doesn’t happen too often. A setup with two bars on each side is also available – although those bars could could also hurt you if you fall off the side of the hammock. Danger lurks everywhere in hammock world!

In a higher price range, you can get wood or aluminum stands, usually forming an arc. It’s an elegant-looking arrangement. Some of these would look very nice indoors, but the biggest ones take up as much space as a small motor boat. So be sure to move the motor boat out of your bedroom before moving the hammock stand in.

The stands vary in length, typically from about 9 feet to 15 feet, measured straight across. Obviously, the stand should be longer than the lying surface of the hammock, and most of them are, but extra length in a stand will allow the cords of a larger hammocks to spread more, and should make it slightly more comfortable. Hammocks with spreader bars always need a longer stand.

Vivere seems to be a common name in hammock stands. Their stands are are available on Amazon and elsewhere. They assemble with nuts and bolts. (The most common complaint on Amazon seemed to be about missing or damaged hardware.)

Hammock Universe sells a 15-foot steel frame that breaks down into fairly short bars that just clip together. It’s as utilitarian (ugly) as every other steel frame, but the assembly method means it disassembles down into smaller parts, making it easy to take apart and move. They also sell a arc-shaped bamboo stand, which, they claim, is more durable than the hardwood stands from other manufacturers.

My Choice

I checked quite a few online sites. In the end, I ordered through Hammock Universe. They got good reviews, and were very quick to answer my questions.

2018-08-15

 Posted by at 8:51 am
Aug 112018
 

Some time around 1968, when we lived in England, we got a Spirograph set for Christmas. It seemed a strange gift. The box was intimidating and adult – more like a drafting set than a toy. The cover showed a businessman working with the system, while his wife and children looked on in admiration and delight. Fun for the whole family, although only dad can touch it.

It become more interesting once we kids started to play with it. I needed help setting up the paper – it had to be fastened to a cardboard backing with push pins, then more pins were needed to hold a toothed ring in place, but then I started moving the gear around the ring, and it became an interesting challenge. The first problem was learning how to move the pen without sending the gear sliding away from its teeth and out of control. This could be infuriating. One slip and the wheel would go skidding across the sheet, ruining the pattern.

The set came with a tiny container of push-pins for mounting the plastic pieces onto the cardboard base. Once the cardboard had acquired enough holes, it became hard to get a good fit, and the plastic pieces tended to slip. I don’t think the set came with enough pins to account for the inevitable losses. You needed four to hold the paper down, and another four to hold the ring in place, so if you lost a few, the set became unusable until a passing baby found a missing pin with its knee.

Modern sets have done away with push-pins and use sticky putty instead. I’ve often wondered why the ring isn’t mounted on an arm that can swing down flat onto the paper. It would keep things much more stable. Too expensive, perhaps?

The pens were also a problem – the set included ballpoint pens in four colours – black, red, green and blue. Their tips were unusually narrow for the time. Because the set was designed around these pens, you couldn’t substitute a regular ballpoint pen – the standard Biro was too wide to fit. . Other Bic pens were narrow enough to fit the hole, but the tip was too short to reach through the plastic piece. Once the pens ran out – or if a sister had taken them to draw a four-colour horse – you were stuck.

Modern sets use wider holes for the pens, although it’s also much easier these days to buy a variety of ultra-fine pens.

Some combinations of ring and gear produced dull, simple patterns which repeated after just a few revolutions, while others produced more complex patterns that might take dozens of revolutions to complete. That was a part of the fun – you never knew what sort of pattern would appear, although, over time, I started to remember the combinations I liked. The best ones were those with the most ink around the holes.

The enclosed booklet included a gallery of possible patterns, in colour, and the instructions to create them. Many are a bit of a cheat – you draw a bit of a pattern, then shift the gears by 10 teeth and draw another bit.

For me, the holy grail was the one on the top row, second from the left – a circular pattern in red, green and blue, using the 150/105 ring and and the 52 gear. (The numbers referred to the number of teeth on each gear.) It’s a continuous pattern – no nasty jumping of teeth required, although you did need to change pens after each 18 loops. The sharp angles made it hard to complete without slipping.

Obviously I wasn’t the only one drawn to this design, as the same pattern has featured on the covers of many most Spirograph sets since the 1960s.

There were other, even more complex patterns, but most were impossible for my hands and stayed forever out of reach.

The old box cover also showed an owl drawn mostly from a series of Spirograph patterns. I don’t remember ever trying anything like this, or feeling any urge to. The pleasure of it was creating abstract patterns. Making Spirograph owls is Just Wrong.

Spirograph was invented by Denys Fisher, a British engineer who produced cannon parts for NATO. When not crafting weapons of destruction to annihilate the Red Menace, he played with automatic drawing machines, and made some devices from Meccano, the classic British building set.

If he were doing it today, he’d be more likely to use Lego Technik, like the guy in this video. The video shows the basic ideas well. A set of arms creates a shape. A turntable advances the drawing at a certain rate.

These kinds of drawing machines have been around for a long time. They were usually big, heavy, tabletop devices. Designs from the 1800s were used to create the complex patterns of lines used on banknotes. A repeating pattern might gradually change in size while the paper is slowly shifted. There had also been previous toys based on this kind of design, with a moving arm and a turntable.

Denys Fisher came up with the idea of turning a set of gears into a toy. The use of gears (rather than, say, moving arms with wheels and pulleys) meant that each pattern would come neatly back to its starting point. The product was an immediate success and won awards. Spirograph was quickly licensed to Kenner in the United States. The North American editions boot the businessman dad from the box cover and show kids having the fun.

Even people who have been turned off mathematics still find the graceful shapes of Spirograph pleasant and relaxing to work with. It shows how people can enjoy patterns that are strongly mathematical.

Modern sets don’t seem to have the same pieces as the set I had as a kid. The original set had 18 wheels, two rings, and two racks. Most newer sets drop a few of the wheels, or one of the racks, The current “original” set has only 15 wheels, two rings and and one rack, although it adds a few odd-shaped pieces. The “Super” Spirograph (now made by Kahootz Toys) is the cheapest set that has all the pieces in the original, the odd-shaped new pieces, as well as a set of snap-together customizable track pieces. It’s a fairly expensive set, so it’s probably better to stick with the basic version and put up with a few missing pieces.

I figured there must be computer versions of Spirograph, and, of course, there are. One nice interactive version, modelled on Spirograph, is Inspirograph. The developer worked hard to give it an organic feel and avoided what must have been a strong temptation to control everything with number menus and sliders. You can use a mouse to roll the wheel around, or press cursor keys to move it semi-automatically. I like the fact that, if you start to go over a line a second time, it actually produces a heavier line, just like in the real thing.

Another interesting development is WildGears, which began as a Kickstarter project making more sophisticated Spirograph-like rings and gears. They allow larger patterns, and a much wider array of types and sizes. The kits are laser-cut from a sheet of acrylic. They’re more expensive than Spirograph starting at $40 for an extensive starter set, up to nearly $800 for the complete, enormous range. At those prices, this is something the old-fashioned businessman dads will use while their adoring families look on in admiration.

 Posted by at 3:29 pm