Next thing to consider is a loop for the end of the line. The Alpine Butterfly can be used, and there's another with a cool name: the Double Dragon. Both have a significant weakness for casual practical use: you need to learn a second way to tie them around a ring or the center of a long bar.
There's a classic knot that doesn't have this problem: the bowline. It's an excellent knot, easy to tie, easy to remember, and you ties it the same way through a ring as you do to use it on a bollard.
The bowline has a weakness though: it holds well with steady tension, or if it's not shaken, but given the right conditions (like floating in water) it can come undone. See Grog's description (linked) for a story
Note that the "weightless" condition imposed when a rope is floating on water is very different to the "one gravity" environment in air - the standard bowline is a very good knot for most conditions.
There are stronger bowlines though. One, called the Water Bowline, is just a little harder to tie and undone, but doesn't loosen in water. There's another called the double bowline, but the Water Bowline has another advantage: it can be "upgraded" to a "Monsoon Bowline" which is a little harder to tie again, but very secure.
See below for descriptions and links..
If necessary, practice the Bowline first until it's natural (it's easy to tie and easy to remember)
One thing will help with the Water Bowline; create the loop (Grog's picture 2) by twisting the rope. If you're holding the rope in your left hand, twist with the right, and hold the loop with thumb and one or two fingers of the left hand. Then the right hand takes the end "up, around, down" to form the knot.
Next the Water Bowline.
Here we make two loops: bottom loop first, exactly as with a Bowline. The second loop is further up the "long side" of the rope - make the same twist as the first, then put it on top of the first loop (creating a clove hitch) - see Grog's pictures 4 and 5 for this. Control the result with the left hand - I put two fingers through the center of the clove hitch and use my thumb against those fingers to hold it.
Now thread the end of the rope exactly as for the normal bowline, but through the clove hitch as a whole (as you do it you'll see why I have my fingers inside the clove hitch).
Tighten moderately as though it was a normal bowline, which will draw up the top half of the clove hitch. Then draw up the lower half using the appropriate "side" of the loop. After that set the knot as a whole.
Next the Monsoon Bowline. The relationship between this and the Water Bowline is a little like that between the Water Bowline and the normal one: it's a minor modification to the base knot. You should be able to tie a Water Bowline without thinking about it before you learn the Monsoon.
Grog doesn't have an animation for this knot, but there's a good picture here you can use:
Look carefully at the first of the large pictures until you can see the Water Bowline clearly, then make one with a loger end section than usual, and thread it as shown.
A quote from notableknotindex.webs.com:
The Monsoon Bowline is ... designed for the occasion where slick, springy rope subjected to severe or persistent slack motion must stay tied for extended periods. While this loop maintains jam resistance and supreme security, it sacrifices compactness, simplicity, and ease of adjustment.
After you've tied it a couple of times you'll decide not to actually use it until there's a hurricane warning on the weather report Even so, make sure you practice it a couple of times, and store the picture in your phone or tablet as a reminder.
Edited by Gordias, 07 November 2014 - 03:21 PM.