I've come up with a way that's really fast to set up, especially if you know your knots. If you don't, you can substitute almost all knots with some form of hardware if you prefer, but it's really worth learning the knots to reduce gear. They're all also useful in many other places (for example, I use the round turn and two half hitches to tie my guy lines to my pegs).
For this setup, you won't need very much gear:
* 10m (33ft) of kernmantle cord (rock climbing rope). I use 5mm rated at 6KN (600KG static load), and it's a good idea to not use cord much weaker than this. There is actually a hell of a lot of force put on this rig to keep it all taught. 10m leaves me qith quite a bit spare, but I woudn't go below 8.5m
* Several small karabiners. The ones I use in the pics are 600KG rated ones from Kong, but as long as they'll easily cope with the weight of the gear you're hanging, you'll be fine.
* A (hammock) tarp. I use an ENO ProFly I bought on eBay. The nice thing about this fly is that it comes with tensioners attached to the guy line attachment points, making setup easier: you can just loosely tie the guy lines then tension everything once it's all positioned.
* Tent pegs. I use some made my DAC, they're super strong and light. I won't be showing the tarp pegged out, I assume that's too obvious to bother with.
* Hammock (Optional). This setup will work just as well for someone who's lightweight camping with just a tarp instead of a full tent.
The image below shows the final setup, without the pegs (because I was too lazy and kneeling on damp ground in jeans is no fun). My pack is hanging under the tarp so I could do a lot of this setup in the rain and keep it dryish.
Step 1: First Tree
There's not much need to be too cautious about how big the loop around the tree is, as long as it's not tight around the tree. The smaller the loop, the more force is exerted on the rope.
Step 2: Attach to Second Tree
To tie this knot:
* Put it around the tree.
* Tie an alpine butterfly* in the part of the rope coming from the first tree about 60cm (2ft) from the second tree.
* Put the end of the rope through the alpine butterfly. We are creating an ad hoc pulley system to tension the line more easily.
* Next put the end back around the tree. We're going to tie a round turn and two half hitches, because it allows us to keep the tension on the line while we tie off. At this point pull on the end of the rope to put the tension into the system.
* Keeping tension on the end, wrap it around the tree again. This is how we keep the tension while finishing up the system, there's a lot of friction in that round turn meaning it won't slip.
* Now to tie off, we tie the two half hitches. Sorry about the sun in the first pic of the first half hitch. To make this easier to untie later, it's a good idea not to pull all the rope through when making the first half hitch so you make a loop. You'll use this loop to tie the second half hitch. It's hard to see what I mean from the pic (since I didn't actually do that when taking these photos, i made the loop on the second half hitch).
* Tie another half hitch using the loop
* I usually tie another half hitch out of habit (makes it clearer from a distance that the knot's tied off, useful when building rescue rigs). this image shows the finished knot.
At this point you can clip on your gear. I've found it's quite nice to have such easy access to my pack when in my hammock, and it acts as a bit of a wind break for my feet (but only a little). All I have to do to access my gear is slide it along the ridge line, the carabiners make it really easy slide.
If you're wondering about the waist strap, it does touch the top of the tarp but should stay dry. Since there's so much weight on the ridge line it hangs quite low below the tarp when its taut meaning that things won't get too wet. In this picture my pack still has my sleeping bag and hammock and all my other gear and it still won't hang this low.
If any of the pictures are unclear leave a comment and I'll take some more and update this post.
* I have chosen to not link to the animatedknots.com article on how to tie this knot, because it teaches it in a way that is dangerous in situations where the line may come under load. This instruct able is not a place where this is likely, but when using it for things like rock climbing (or roof safety systems or rescue like I do), it's never a good idea to wrap a rope around your hand. If you do, you might lose it (the hand, not the rope).
Step 3: Attach Tarp
We'll be using another knot for this step, the rolling hitch. I put a few extra turns in mine so it bites harder to the tarp stays taut. We're using this knot because it grips to the rope like a prusik knot but it doesn't require a loop in the cord. When tension is placed on this hitch in one direction it will not slip, but it is easy to move in either direction if you hold the knot itself and slide it.
* Chuck the tarp over the line.
* Next wrap the guy line of the tarp around the ridge line three or four times going back toward the tarp.
* Then tie a half hitch on the side of the knot away from the tarp (making sure to wrap the same direction as in the previous step). Again, I haven't pulled all the cord all the way through so it'll be easier to untie later.
* Tie another half hitch using the loop created in the previous step. This ensures that if the end gets pulled, it won't untie by itself. Sorry the pic isn't clearer, you should be able to make out the second half hitch tied with the loop on the left, then the first half hitch just to the right of it.
The last picture shows the same knot tied in the other end of the tarp.
Step 4: Tension and Finish
If you don't have access to tensioners on your tarp you're still in luck, though you'll never get it quite as taut. All you have to do is slide the rolling hitches along the rope. To do this, you just hold the hitch in your hand and slide it to the desired position and tautness.
All that's left is to peg out the corners of the tarp (not shown) and then erect your hammock in the shelter of your tarp. Your gear will stay dry and off the ground and you don't have to get your hammock wet in the rain.
This is my first instructable so I'm eager for comments and suggestions.
Until next time!