Double Soft Shackle
This double ended soft shackle is the 4th generation of a design that can attach to a pair of eye spliced jib sheets to the clew of a sail very quickly. It is also the 5th version of this generation as improvements were made to make the shackle stronger. In use, the shackle is secure around the jib sheet prior to being "clipped" to the clew. This version is easy to make and has the advantage of a non-constricting hold on the jib sheets. There are links to the previous versions at the bottom of this page
OverviewThe shackle has two sections. The short section will attach to the Stopper Knot. That needs to be long enough to allow the shackle to open enough to pass the stopper knot thought the loop. I used 4 inches. The shackle is held together with four knots. On the end forming the stopper for one of the shackles is a diamond knot. The other end attaches to a separate stopper loop which also has a diamond knot. The center of the double shackle has what is basically a double bowline and tripple strangle hitch. I started with simpler knots, straight bowline and single strangle hitch and kept increasing the complexity to eliminate failure modes.
TestingI tested this shackle with 7/64 Amsteel using a 5/32 stopper knot. The shackle more or less exploded on failure with breaks at the eye, the bowline, and the strangle hitch. This design went through many iterations, each stronger than the one before. Note that while the force on my 30:1 power winch was considerable, nearly as much as I could manage, it is only roughtly calibrated and the force was less than the line breaking strength as I had a test section of straight line and it did not break.
My estimate of the the force is based on measuring the stretch of the 7/16 XLS line that I use around the winch. The stretch was 3/4 inch in one foot in my last measurement before the shackle broke. A 53 pound weight hung on the handle at right angle to the nandle will stretch the line 5/8 inch. Working the math on this would indicate that the shackle broke at 1,900 pounds, which exceeds the rated breaking strength of 7/64 Amsteel. However the test section did not break so it is not as strong as the line, but it is strong.
I used a larger stopper knot as otherwise the stopper knot breaks before the shackle.
To view the carnage from all the testing click HERE.
CAUTION: Be sure to do your own testing before using these. Safety is your responsibility not mine.
Note: For maximum strength of the double soft shackle, use the next size up line for the stopper knot.
Using the calculator from the Soft Shackle Howto, measure off a piece twice the length of the first mark. Double the line over, tape it at the fold, and tie a diamond knot using the two ends. Lock it by placing the ends in a vice and pulling on the loop with a lever of some kind. I use a hammer with the had as the fulcrum and the loop on the handle near the head.
How to Make The Double ShackleThese instructions are for 3/16 Amsteel. The shackle uses 56 inches of line. For other sizes, just scale these numbers by the ratio of the line size. For example, for 5/32 Amsteel, multiply all these numbers by .833 so instead of 56 inches use 47 inches.
Ad by Google
The information on this web site has not been checked for accuracy. It is for entertainment purposes only and should be independently verified before using for any other reason. There are five sources. 1) Documents and manuals from a variety of sources. These have not been checked for accuracy and in many cases have not even been read by anyone associated with L-36.com. I have no idea of they are useful or accurate, I leave that to the reader. 2) Articles others have written and submitted. If you have questions on these, please contact the author. 3) Articles that represent my personal opinions. These are intended to promote thought and for entertainment. These are not intended to be fact, they are my opinions. 4) Small programs that generate result presented on a web page. Like any computer program, these may and in some cases do have errors. Almost all of these also make simplifying assumptions so they are not totally accurate even if there are no errors. Please verify all results. 5) Weather information is from numerious of sources and is presented automatically. It is not checked for accuracy either by anyone at L-36.com or by the source which is typically the US Government. See the NOAA web site for their disclaimer. Finally, tide and current data on this site is from 2007 and 2008 data bases, which may contain even older data. Changes in harbors due to building or dredging change tides and currents and for that reason many of the locations presented are no longer supported by newer data bases. For example, there is very little tidal current data in newer data bases so current data is likely wrong to some extent. This data is NOT FOR NAVIGATION. See the XTide disclaimer for details. In addition, tide and current are influenced by storms, river flow, and other factors beyond the ability of any predictive program.