The Double Constrictor Knot is almost the same as the Constrictor Knot to tie but it has very different properties.
The Double Constrictor Knot is permanent, and can bind things together so tightly that it can cause damage.
For academic reasons, I used two double constrictor knots tied with nylon cord instead of hose clamps when I installed a check valve in Wisdom, back in August 2013. The check valve is on the shore water inlet and is subjected to city pressure when a shore hose is connected. I thought this would be a good place to try it out, as the high pressure would expedite any failure. I tied the double constrictor knots where hose clamps would go and then pressurized the system, expecting the hose to slip off the check valve, or at least drip a little; but nothing happened! It was completely dry!
I left it on for the rest of the day to see when the dripping would begin but it was still dry, so I decided to leave it on for the rest of the week, then rest of the month, and now 2 years later, it is still on there and no leaks!
This knot can be used to hold a broken tiller, a splitting boat hook, or as a "temporary" hose clamp. I say temporary because it will hold just as well as a steel one. This knot truly lives up to its name, it will constrict and then hold forever.
Like all knots, there are advantages and disadvantages. The Double Constrictor Knot is considered permanent once it is tightened down. It really is permanent because it is almost impossible to untie. I have always been forced to cut them off because they will not loosen once tightened.
Tying the double constrictor is almost identical to tying a constrictor knot, the only difference is one extra wrap going from Lower Right to Upper Left when making the X. Then tighten it down and it will hold permanently.
I didn't tighten this knot all the way because I wanted to have the line back for other knots.
By using marlin spike hitches, you can tighten the double constrictor knot fully and count on it as a permanent knot.
The marlin spike hitches allow you to tie the tails to sticks or rods that you can then pull on like handles.
To really tighten the knot as much as humanly possible, you must sit on your butt and balance yourself. You will pull up on the stick in your hands while simultaneously pushing away on the other stick with your feet. This action will involve your strong leg muscles into the tightening process, securely tightening the line to permanent levels.
Once finished, you can simply cut the tails off the knot and rest assured that it will hold forever.