Round Turn and Two Half Hitches
Other than a cleat, the round turn and two half hitches is the mostly commonly used knot for securing a boat to the dock. One of the great properties of this knot is that it will not come undone, even when under extreme tension, and can even be undone when under a load. The most important part of this knot is that it requires a post or dock railing for the line to wrap around.
How to tie it
Step 1: Wrap the loose end 
of the line around the pole.
Step 2: Loop the line around 
once more. This creates one and a half wraps around the pole.
Step 3:
Cross the short end 
of the line over the tail. This makes a shape similar to the number "4".
Step 4: Bring the short end under 
and through the loop in the "4".
Step 5: Pull tight.
Step 6: Repeat steps 3 
to 5 to create the second half hitch.
Common Errors
The basis of this knot is pretty simple. However, there are three common errors that people commonly encounter. These are:
- only wrapping the short end around the pole once, so it does not completely encircle the pole. Although the "second" turn may seem unneccesary, this is what gives the knot it's strength;
- tying too many half hitches. This does not alter the strength of the knot at all, but two half hitches is enough; more half hitches just means more time spent untying the knot;
- occasionally, when the knot is pulled tight, the half hitches look more like a reef knot than two loops. If this is the case, manipulate the knot so it looks correct. This can be avoided by pulling the short end at 90 degrees to the tail when tightening the knot.
If your knot still does not look right, watch the demonstration video.
