Knot: Somerville Bow Line

1. Wrap the rope at least twice around the column (so 4 strands everywhere).
2. Leave about 10cm loose at the head.
3. Bring the tail over the top of the 4 strands.
4. Make a loop in the tail. The loop should pass under the tail. So now, the 4 strands and the loop are all laying under a section of the tail.
5. Take the head up through the loop and back across that section of the tail and feed it under the 4 strands coming up through the loop again. Probably easiest to reach 2 fingers through the loop and under the strands to grab it.
6. Tighten the loop.

The Somerville bowline is a secure knot but it is very hard to release it if the tail if under tension. You first have to ease the tension but that may be difficult. If needed, consider the following modification.

Slipped version

• At step 2: leave about 20cm at the head, instead of 10cm
• At step 5: above when feeding the head through the loop, fold it over so that you feed 4 strands through the loop and tighten on that. The head never goes through loop.
• When you need to release, pull the head. This will pull those 4 strands back out of the loop and the know will release.

Other notes

After tying, the head and tail will point in a opposite directions, perpendicular to the 4 strands. When you wrap the strands around the column, if you choose to put the head above the tail then at the end, the head will point down and the tail will point up and vice-versa.

The loop in step 4 can pass over the tail if you really want but then in step 5, you have to bring the head under the strands that are around the column but then into the loop from the top. Otherwise the loop will not form a knot. It's easier to form the loop this way but it's definitely harder to feed the head into it. Maybe it's useful sometimes...

Different technique is in this tutorial.