Posted by Darrell Nicholson with Drew Frye at 05:46PM - Comments: (5)
My previous blog post on rig inspection prompted a question about how to splice old ropes, specifically ropes that need to be shortened to eliminate chafed sections near the original splice.
We passed on some common solutions to this problem, but remained unsatisfied with these answers. It wasn’t long before the ice-climber among our contributors, Drew Frye, decided to grab this rope by its braided cover, so to speak, and see where it leads.
Frye tested a variety of ways to stitch eyes in the end of a rope, and then tried to break the ropes, to see how well the stitched eyes held. In the end, he found that when done correctly, stitching can produce predictable breaking strengths.
There are several ways to stitch or whip eyes in the end of a rope. Frye was familiar with some of the techniques, since climbers often stitch loops in their ropes because they are too stiff to splice. But without testing, it was impossible to tell which stitching method—perimeter round-stitching, basting, seizing, and some hybrid approaches—was the most reliable for sailing applications. Frye’s full report appears in the October 2014 issue of Practical Sailor. A follow-up on stitched spllces after two years in the field appears in the June 2016 issue.
Here is a brief description of the method that Frye found worked best, round-stitching. Although we don’t recommend stitched eyes for halyards on large boats, they can be used for genoa sheets, travelers, vangs, and even main sheets—with wider applications on smaller boats, where the breaking strength of the line often far exceeds the anticipated loads. Like splices and knots, stitched eyes are weak links in any rope, so it is important to protect the stitching from UV and chafe (we’re testing several methods, ranging from paint-on coatings, to heat-shrink tubing), to inspect the stitching regularly, and to re-stitch a new eye at any sign of wear.
Perimeter round-stitching will take place over a length of rope that is the equivalent of six to eight times the diameter of the rope. For example, stitching 3/8-inch line requires about 2.5 inches of available line for stitching, not counting the very tail of the line (about 3.8 inches in length) that will not be stitched. If you plan to taper the end to reduce snags, then you can pull out a length of core from the end that is twice the diameter of the core, and sew the cover to the standing part. This optional taper is only to reduce the chance of snagging; it does not contribute any strength.
To determine twine size (we used waxed Robline Dacron twine, rated Best Choice in Practical Sailor's test of whipping twines), conventional wisdom holds that it should be 1/12 to 1/16 the diameter of the line. We doubled the twine we used (effectively doubling the diameter), and found that slightly larger diameters did not hinder performance. For ¼-inch line with a breaking strength of 2,500 pounds, we used twine with 52-pound breaking strength. Polyester (or Dacron) twine was preferable. Kevlar and Dyneema twine tended to cut into the rope.
To determine how many stitches are required, take the breaking strength of the rope and divide it by four times the twine strength. (When using this formula, remember that the stitches are doubled.) As a safety margin for our field-testing on the boat, testers took this number and added another 50 percent, so if the calculation gave us 12 stitches, we used 18.
We spaced the stitches about two cover strands apart (see photo) and found that this created a stitched eye that reduced the line’s strength by only 15 percent.
Step-by-step Perimeter Round Stitch
- Form a loop in the rope with the bitter end extending at least eight times the rope diameter after the loop. You can insert a thimble if you like, but this is not required.
- Begin by forming a loop in the twine and hitching around one side.
- Pass round stitches through both lines. The stitches should vary in location in the core, staggered from barely past the cover to near the center.
- Stitch downward toward the bitter end, pass the needle through, and continue stitching up the other side to the throat of the splice.
- Form a round seizing at the throat, using No. 3388 from the “Ashley Book of Knots” for guidance. (Round seizing is also found in most other knot books.) The seizing should be two layers—lower turns and riders—about eight to 10 turns or as long as twice the diameter of the rope.
- Finish the seizing with a seizing hitch (“Ashley Book of Knots” No. 3390) or flat knot (“Ashley Book of Knots” No. 3385). This throat seizing is vital as it protects the first few stitches from the peeling force generated by the eye (throat) angle.
- A seizing may also be applied at the tail end, where it helps with wear.
- A thimble is not needed if the radius of the attachment is about the same as the diameter of the rope. A bend in the line that is equal to one times the diameter of the rope will weaken the rope by about 50 percent, but there are two legs and only 50 percent is carried on each side. The diameter of the hardware we tested against was half the size of the diameter of the rope, and we never broke a line at the bearing surface.