Monday, November23, 2020
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A Better Soft Shackle

Revised 1/20/2014

Note. The calculator on this page will work in inches or mm. Just select the line size that you want and enter your numbers in the same units.


I make and use a lot of soft shackles to attach my jib sheets. The normal soft shackle is rather difficult to open and to milk closed. With age, it gets every more difficult to use. The alternative Kohlhoff style looks a bit insecure although under load it is perfectly secure. This version is a bit of a hybrid with hopefully the best properties of both. The eye is easy to open but can only be opened just enough to fit the stopper knot through it. Almost any slight force will close it quickly. The basic construction is a pass through eye, a shackle section of about 2 1/2inches for the 5/32 line below, 3 inches for 3/16, a pass through lock and then a bury of the other strand into a body section of about 5 1/2 inches, another pass through and finally a diamond knot.

The Shackle




Closing the Shackle





This shackle is very secure. I can pull on the part of the shackle that tends to open the eye and yank as hard as I want on the shackle and it won't come undone. The only way I can get it undone is to open the eye and push the diamond knot through while holding the eye. The slightest force closes this shackle. You don't have to milk it closed.


Shackle Length Tip of eye to insdie of knot
Line Size Diameter of Amsteel
Shackle ID Inside diameter closed
Capacity Max diameter of load
Interior size inner stretched size
Line Length Total rope needed
First Crossover From tip of eye
Exit point of bury From tip of eye


Use the calculator to the left to help decide what size shackle you want to make. Enter the lenght and the line size and click calculate.

Cut a piece of Amsteel the for the desired length shackle. Don't make any marks yet. Fold the line in half and pass one end through the other at the half way point. When you are done, form the eye and note that one tail is longer than the other. The eye should be about the size of the line.

NOTE: Actually, the eye should be a bit larger than just a single line. The eye will be around basically two lines so something more like 1.5 line diameters is a better goal. Under use, the eye tends to open and the line tends to get thinner so I personally do not feel this is too critical but it has been brought up so I thought I should mention it.

Measure down from the tip to the first crossover point (3 inches for 3/16 Amsteel - use calculator to scale for other line sizes) and pass the longer tail through the shorter one. Before you do this, you might want to check the loop sizes. Stick a straight pin or small fid through both tails at the point you will be passing the longer tail through the shorter one to lock up the lines. Work the loop closed and see that there the eye opening is about the line size. I use a fid the size of the line and work the eye closed around the fid. Then open the eye and see that it will be large enough to pass the diamond knot through, about 6 times the line diameter.

Next bury the shorter tail through a length of the longer one. We want this to exit about 1/2 inch short of the shackle length desired to allow for the brummel section before the knot. We need to allow 20% extra for the amount that the line will shrink when the core section is inserted. For this example we want an eight inch shackle. We have 3 inches in the shackle part and we want to leave 1/2 inch for the brummel. That means we want the body part to be 4.5 inches and 22% of that about an inch. Make a mark 8 inches less 1/2 inch plus 7/8 inch or 8 1/2 inches from the tip of the eye. Better yet, just look up the "exit point of bury" number in the calculator. Measure from the top of the eye and make a mark before you start the bury. End the bury of the core tail at that point.

Pull everything tight and make sure the eye opening is correct. Insert the tail that was the cover through the tail that was the core.

Here is a close up.

Pull everything snug. You may find that one tail is longer than the other by some small amount. Cut them so they are the same length. When you are done locking the diamond knot, the tails sticking out of the knot should be the same lenght if both are equally tight. Cutting them now will make it easier to make the diamond knot.

Tie the diamond knot using the two tails. Follow the instructions in the Soft Shackle Howto starting where you cut the two ends to be the same length. It is table row number 13.

Lock the knot. I like to put the tails through a metal bar with a hole in it and pull on the tails with vice grip pliers. Next I secure the eye to a 4x4 and pry on the ends of the knot against a pin 8 inches or so away on the 4x4. This will lock the knot. It also works to put the two ends of the line in a bench vice and put a steel rod through the eye and pull very hard. Get some leverage by using the rod as a lever, locking the end against something solid and pulling back with the eye just a short distance away from the end of the bar where it is secured.

When the knot is locked, you can bang it against the table and it will sound like knocking a wood ball against the table.

Cut off the tails but leave a little bit. Leave an inch if you don't lock the knots, 1/4 inch if they are very tight.

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