Bowline! Quick and Easy!
(See this in a Slide show)
It's cold, you have neoprene gloves on, and the boat is being dragged downstream so you have to wrap your arm around the trunk to hold yourself in place AND tie this quickly. This is the method we use to do deep water salvage where time and visibility are limited.
1. Lay the rope on the palm of your hands, thumbs out, free end (running end) to the left ( I am right handed, you may want to change this if you are left handed-it helps when you form the loop in step 3).
2. Looking at the right (towards the standing end) hand, form a loop by rotating your thumb to the front and over top of the running end of the line being held by the left hand.
3. Using the same hand you used to form the loop, reach through the loop formed and grab the standing line from beneath, then pull it up through the loop.
4. Now run the loose end (running end) through or around the object you want to tie off to and pass it through the loop you just made, as shown.
5. Finally, while holding the line on both sides of the knot, give a quick pull on the standing end rope. The running end is pulled through the loop, the knot inverts, and the bowline is done!