Tuesday, November 19, 2013

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

Have you ever tried to splice old double-braid line? I have. And saying that it is "difficult" misses the mark by an order of magnitude. Over at Sail Delmarva Drew gives us a lesson in an alternative...
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? Most whipping thread is about 50- to 60-pound test (I use 90-pound Kevlar, just because I have it), and doubled that suggests about 25 stitches on each side to reach 5000 pounds. Sure, it is not loaded in-line, but most of the load (about 65% in testing) 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 35% of the load. The results is that the stitching is only carrying a working load of about 1000*0.35*(1-0.65)=122 pounds and a line failure load of about 610 pounds (assuming 5000 pounds for aged 1/2" Stayset); 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.

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.

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 Manula only calls for 3 1/2 to 4 rope diameters and I've got 4 1/2 diameters without counting the taper.

(Note: when I discovered the line was Warpspeed, 22000-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. 
And if you have concerns about the strength of sewn eyes, Drew addresses that in a follow-on post, which you should read.

No comments:

Post a Comment

Related Posts Plugin for WordPress, Blogger...