Can't Splice Old Line? Try a Sewn Eye.

rev. 10-27-2013, rev. 8-1-2024

Splicing is the gold standard for forming permanent eyes and joining lines; unfortunately used double braid generally lacks the flexibility required for splicing; the cover won't open and the core won't slide. Knots are a standard solution and work in most cases; yes, there is some loss in strength, but lines generally die from chafe and I can't remember having one fail at the knot, other than in testing. But sometimes there simply isn't enough space or a knot will snag.

Seizing is traditional and just as reliable as ever. I've seized a dozens of eyes over the years and never had a failure. I helps if you cover them for UV and chafe protection, but if the seizing is double layer like the old days, the outside layer is the UV protection and the inside layer holds the load. But seizings are long and stiff and can hang up, since the tail is neither covered nor tapered. So occasionally I use a hybrid sewn/seized eye. This isn't an idea I dreamed up, it is an old one that I read of many years ago in the New Glenans Sailing Manual. They also speak of stropes, the precursor to soft shackles.
  ____________________________________

First I remove about 1 1/2 rope diameters of core. This will allowed the end to be stitched down to create smooth taper. The New Glenans Sailing Manual calls for 3 1/2 to 4 rope diameters of core and I've got 4 1/2 diameters without counting the taper.

How much stitching is enough? Select a whipping twine that is 10-15% of the line diameter; for example, 7/16-inch line is about 11mm, so #10 whipping twine is a good match.  In this case I used 90-pound Kevlar this time, just because I had it and because it is about the same strength as #10 twine. Doubled that suggests about 12 round stitches on each side to reach 5000 pounds. Sure, it is not loaded in-line, but most of the load (about 35-55% in testing, depending on the roughness of the line) is actually carried by line-to-line friction, just as in a seizing. Also remember that due to friction of the eye around the shackle or fitting, the free end is only carrying about 25-35% of the load, depending on line stiffness. The results is that the stitching is only carrying a working load of about 1000*0.30*(1-0.45)=165 pounds and a line failure load of about 825 pounds (assuming 5000 pounds for aged 1/2" Staset); not nearly as demanding as you would guess and as usual, the splice is stronger than the line. The stitching is scattered so that some are in every part of the core.

Whipping Twine Summary

Twine Number        Diameter       Strength

#4                            0.4 mm         35 pounds

#8                            0.8 mm         70 pounds

#10                          1.0 mm         90 pounds

#15                          1.5 mm         130 pounds

(In retrospect Kevlar may be a  poor choice, given its poor performance in flexing applications. Although the stitching does not flex, more polyester twine might be more reliable.)

After stitching I add 2 seizings for good measure. The throat seizing is the important one, as it keeps the first row of stitches from getting over loaded.
(Skip the seizings; they add nothing and become loose as the line shrinks under load.)

(Crowd as much stitching into the first inch of the tail as possible if working with nylon; the nylon stretches so much under load that only the first inch carries any real load. Think about playing tug of war with a bungee cord. A double pass, center and edge, can be a good way to do this.)

Then cover it with something for UV and chafe protection. Heat shrink is fast and poor choice (doesn't last). Webbing is better in severe applications... like winching a sheet along a shroud.

The New Glenans Sailing Manual only calls for 3 1/2 to 4 rope diameters and I've got 4 1/2 diameters without counting the taper.

8-1-2024. The video demonstrates a slightly different method, called a sailmaker's eye. It is not quite as strong in lines larger than 1/2-inch, but it can be >90% strength in smaller lines and is more abrasion resistant for applications where it can't be covered. The clips were made for a Good Old Boat video.

  (Even though the load is carried in the first 3-4 diameters, pull testing shows that stitching in diameters 5-6 does contribute to splice stability. Just don't count those threads in the calculation; only those in the first 4 diameters.)

(Note: when I discovered the line was Warpspeed, 22,000-pound test, I added another solid layer of whipping. Also good for abrasion.)

Notice the strope in place of a shackle. Less steel to flog, removable, and as strong as the larger line because it is doubled.If the eye is small it can't fall out easily. The failure point is always the same; the loop cuts off the stopper knot.  

After just 2 days I learned that heatshrink is not enough, not when winched across a cable shroud. I also switched to Amsteel soft shackles (home-tied) for a bit more long-term security. That and the they fit the clew better; the yacht braid stropes worked fine and would no doubt last for years, but I really didn't have room for 2; the big knots would jam on each other. The yacht brain

strope would be fine for a single set of sheets.  
  

------------------------------

 rev. 1-1-6-2014

I'm currently engaged in a much deeper exploration of the subject for an up-coming Practical Sailor article. I've learned more than a few things, a few highlights of which I have added above in RED.