Saturday, July20, 2019

Soft Shackle Variation #4

Double Soft Shackle

UPDATE: The picture below is an improved version of this shackle. In testing the diamond knot works but it distorts. Given the stresses involved, a double fisherman's knot is more approproate and easier to tie although somewhat difficult to get exactly the right length. The shackle shown uses the dimensions in the table except 1 inch was added to the center knot section and the knot was put at one end. (This added length was not necessary). This gives a longer loop to go through a pair of eye spliced jib sheets. It also allowed one of the tails to be burried inside the "knot" section. I selected the section that needed shortening for the bury. The other new feature of this shackle is the addition of a double crossover to give more stability to the knot. This is probably not necessary with the double fishermans knot as it is very tight and holds the shackle firmly.


In application, it is important to keep the shackle from falling off the sheet eye splices when the shackle is not connected to the clew. For this the long side of the shackle is attached so that the loop is below the knot so that it cannot slip past the knot.


This is a dual ended soft shackle that can be used to secure eye splices in jib sheets with one end and then attach to a stopper loop tied to the jib clew with the other end. The knot in the center is a three strand diamond knot.



Below is a more compact version designed to make the length from sheet to clew short. Notice that I used the next size up for the line on the clew ring. IMG_7832

A variation to the variation uses the stopper loop around the first shackle loop to provide a termination knot for the second shackle loop. This creates a stand alone shackle with two ends. It is also stronger as the load is split on the two sides of the shackle. This makes the load on the knot half of what it is without the second loop. I am using the Kohlhoff style shackles because they allow the body of the shackle to be short thus bringing the clew and sheets closer together.



How to tie the knot


This is the loop. If you are making a double soft shackle, you need to have the crossover for the shackle lock in this loop. The red line would be the section between the two eyes.

Take the "gray" strand and wrap it around the "red" strand as shown.

Flip the "red" line over to get this picture

Grab the part of the grey strand that is above the red strand and flip it 1/2 turn clockwise to get this view.

Now take that loop and fold it over horizontally.

Carefully arrange all the lines so they look exactly like this. In the next step, you are going to take the tail from the right hand eye and thread it through all these loops going under two, over two, under the last one you went over, then over one, under three, and over one exiting in the lower right of this picture. Finally, you need to work the knot to tighten it in the center of the shackle. This takes some doing. I found it helpful to start by marking the knot area with a black marker when I first laid out the line. This made it easy to see which line needed to be pulled which way to bring the knot into form.

Thread the third strand as shown here. The "blue" line comes in from the top and moves more or less left then down and right. Tighten up the knot and you have it. Make sure the knot ends up where you want it, in my case the center.

Dimensions for line

Below are the dimension for a minimum length double shackle using 5/32 line. If you want to make one out of a different size line, scale these numbers by the ratio of line diameter. The table below the picture does that. You may also want to make the shackles a bit longer, in which case add to the 6.5 inch dimension. The insertion point is set to allow the 1.5 inches for the eye in the shackle. Scale this appropriately.


Size Tail Knot Shackle Insert Points Overall Length
7/64 4 1/4 1 7/8 4 1/2 2 3/4 23 1/4
1/8 4 3/4 2 1/4 5 1/4 3 1/4 26 5/8
5/32 6 2 3/4 6 2/4 4 33 1/4
3/16 7 1/4 3 1/4 7 3/4 4 3/4 39 7/8
1/4 9 5/8 4 3/8 10 3/8 6 3/8 53 1/4

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