Just for reference and to make sure I was not saying something incorrect, I did an experiment. I put the stopper loop on a coat hanger that is hanging from a rope in my garage and attached the double soft shackle to a line. With the hanger swinging back and fourth, I can easily and quickly attach the shackle and sheet to the stopper eye with one hand. You basically hold the open eyed shackle in your hand and grab the stopper knot pushing the eye onto the stopper. Then you let go of the shackle, keeping hold of the stopper knot. Gravity tightens the shackle and it is attached. It is very fast.
I have used normal soft shackles a lot over the last year. They are not easy to put on. The idea of my line shackle and this double soft shackle is that with the working part of the shackle straight, it closes very easily. When you double it back, it is not so easy.
In terms of strength, this double soft shackle is not as strong as the line it is made of from but it is very close. In my test, I put about 1900 pounds on a 7/64 line. The line is rated at 1600 pounds so while I put more than the rating of the line, I did not break a test section of line so it is not as strong as the line but close. For the real shackles, I am using 5/32 line which is rated at 4000 pounds. If I was using 7/16 XLS line, typical line for my boat, with a bowline on it reducing the strength by 40% I would have about 3500 pound strength. So, without even going to 3/16 line, I get an attachment that is as strong as I would have using a bowline. The point is, I don't need the double strength.
I do appreciate your correction on the name of the knot. I used the knots I did because I analyzed what broke and modified what I had to make them stronger. There were many iterations and I wasn't completely sure what to call what I ended up with. The double bowline is not a double bowline as it has that line coming back through the "rabbit hole". That adds greatly to the strength but it is not a bowline. I just call it that because it is otherwise a bowline.
By the way, there are many iterations of soft shackles including a new standard soft shackle on my web site. You might enjoy looking it over if you have not done so already.
http://L-36.com
Allen
