If you know any arborists, you will notice they look up a lot. There is a reason for that - arborists, unlike most other mortals, are very interested in things falling on them. So should you be. If you're about to throw a rope in a tree, have a good look at the tree first. If there are any dead or broken branches up there, get a professional arborist to make the tree safe!
In the USA (or anywhere else) I recommend you use an arborist who is a member of the International Society of Arborists (ISA) or the local national body - in New Zealand, NZAA, in Australia, ISAAC etc.
Step 1: What You Need
Have a look at this related link How to Climb a Tree (with prussiks!) - I am working on another instructable on tree climbing too :)
To set a rope in a tree you will need the following:
You need a rope twice as long as the branch is high (ie if the branch is 12m off the ground you need at least 24m of rope). You'll figure out why. Do NOT compromise on the quality of this rope - your life depends on it. Go for a polyester or poly-blend rope that has sufficient break-test to support your life. The IDEAL rope will be a rated, arborist's climbing line which will have a break test of around 5400lbs or 2700kg. There is plenty of yachting rope around that is strong enough - it just isn't break-tested. Polypropylene rope is also very strong - it's just a bitch to work with. OK for a swing, but not for climbing on.
This can be a commercial arborist's throwline (like Zing-it) or monofilament nylon or even sash cord or string. Basically, a thin, slippery cord that you can throw over a high branch. Good-quality throwline is easier to throw and less frustrating, and not highly-expensive, but you can cut costs here without compromising your safety.
The best throwballs are made by commercial arborist's suppliers. Arguably the best throwballs are made by Andy Harrison in NZ (firstname.lastname@example.org) and you can order them via e-mail. They're not expensive, and they work really well. Throwballs are filled with lead shot so they're soft but fairly heavy.
If you're a cheapskate you can throw any heavy object you like over the branch. I don't care if you choose to throw a piece of rail or an anvil - just remember when it comes down it can hurt you. I am not responsible for damage that you inflict to your neighbour's glasshouse or Porsche.
Wear a cycle helmet, a skate helmet, or a climbing helmet. Then the anvil falling on your head won't hurt as much.
A cambium saver
You don't really need a cambium saver. But if you're climbing in a tree and you want to set a rope, use one. It saves the bark, and it makes it easier to climb the tree, and it's easier on your rope. I'm just showing you the right way to do it. I appeal to your deep-green moral conscience.
A cambium saver is a rated load sling with two rated metal rings at either end (pictured). You can improvise one from a load sling or a loop of rope and carabiners, but make sure that everything you use is rated.
Gear advice - never scrimp and save on climbing gear. Find the best price for the good stuff. There are heaps of commercial websites. Start at www.petzl.com and work outwards.
Step 2: Get the Cambium Saver Into the Tree
Attach the throwball to the end of the throwline. Any old knot will work, but there are good knots and bad knots. Do some internet research! You need a knot with a loop that can be easily undone later (like a shoelace knot).
Throw the throwball over the branch. With practice you can shy a throwball easily 20m / 60 ft. Practice in a place where nothing can get broken!! Your neighbour will not appreciate getting socked in the head by a 20g lead weight!
The weight of the throwball will bring it back down to the ground. For obvious reasons, keep hold of both ends of your throwline.
Put the weighted end of the throwline through the SMALL loop of the cambium saver.
Pull on the unweighted end of the throwline.
The cambium saver will now sail up into the tree and flop over the branch with the two steel loops hanging down.
Let go of the throwline.
The weight of the throwball will make it fall back down to the ground.
Step 3: Get the Rope Into the Tree
Untie the throwball from the throwline.
The idea is to tie the climbing line onto the throwline so you can pull it up, through the SMALL loop of the cambium saver, through the BIG loop of the cambium saver, and back down to the ground.
To do this, tie the throwline to the climbing line about a foot from the end. There are lots of hitches that will work for this - research the topic online. Refer to the photos below too.
Now tie a couple of hitches towards the tip of the climbing line, with one hitch right at the tip. The idea is that the climbing line will follow the throwline up the tree, through the cambium saver loops, and back down to the ground. Got it, eh?
Pull on the throwline. The climbing line should run up, through the cambium saver loops, and back down. If it sticks at the small cambium saver loop, try setting the last hitch closer to the end of the climbing line.
Step 4: Where to From Here?
If this is going to be reasonably permanent swing, you can miss out the cambium saver and just set the rope over the branch. Then make a bowline in one end of the rope, slip the other end of the rope through, and pull it up into the tree. Now you will HAVE to climb the tree if you want to get the rope out again.
Because the rope is looped over the branch, it will re-set itself as the branch grows - no etiolation.
A rope through a cambium saver is the ideal anchor for climbing the tree. The friction of a rope over a branch can do permanent damage to the bark
Attach a swing to both ends of the rope, and do whatever comes to mind.
Step 5: Getting Back Your Cambium Saver
Take hold of both ends of your climbing rope.
Look carefully up at your cambium saver. If you're short-sighted or have a long rope, use binoculars.
See which end of your rope goes to the BIG ring on the cambium saver.
Tie an overhand knot in this end of the rope. This knot should be small enough to go through the BIG ring but too big to go through the SMALL ring.
YOU ONLY GET ONE CHANCE TO DO THIS RIGHT - OTHERWISE YOU END UP CLIMBING THE TREE If you don't understand now, you soon will.
Pull on the end of the climbing rope without the knot. The knotted end should sail up, pop through the BIG ring of the cambium saver, catch the SMALL ring, and the cambium saver will fall on your head (unless you move). Any arborist will tell you that it is quite satisfying to have your rope and cambium saver at the bottom of the tree.
Step 6: What Can Go Wrong
Solution: jiggle the throwline until it drops. If all else fails, you may have to climb and get it out.
The small loop of the cambium saver goes through the big one
Solution: You're climbing for sure!
You pull your climbing line or throwline out of the cambium saver, but leave it in the tree
Solution: see above
You pull the wrong end of your climbing rope when retrieving the cambium saver'
Solution: see above
Best you learn to climb trees, 'cos sooner or later you'll have to!
Climbing trees places you in mortal danger if you climb high enough and without suitable safety equipment. Please research tree climbing on the internet. There are recreational tree climbing clubs that can teach you to climb (e.g. Tree Climbers International). Please put your life in danger in a responsible fashion'