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Splicing Dyneema

During a refit of the lifelines on his brigantine schooner, writer Roger Hughes discovers forming an eye splice with Dyneema is easier than splicing double braided line.

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testing rig
Miami Cordage has a ­massive testing rig that will stretch rope to destruction, including naval-ship rope. Roger Hughes

As I detailed in my recent article on replacing the lifelines on my 45-foot schooner, I learned much about Dyneema rope in the course of that project. Dyneema is considerably stronger, size-for-size, than double-braided rope, and stronger than stainless wire of the same thickness. For example, ¼-inch 12-strand single-braid Dyneema has an amazing tensile strength of between 8,000 and 12,000 pounds. By comparison, 7-by-7 3/16-inch wire has a working load of 3,700 pounds. Note: There are variations of Dyneema, and these figures vary from one maker to another. Still, the potential of substituting Dyneema for many lines on a sailboat has become a reality.

I discovered another significant benefit in using Dyneema: the ease with which an eye splice can be formed, unlike the complicated (at least for me) reverse-tuck procedure for splicing double braided line. Unlike double braid, 12-strand Dyneema is hollow, with no center core; to make an eye splice, the tail is first tapered by removing pairs of strands, then the end is buried deep inside the standing part and lock-stitched. This is an easy operation using a special 14-inch-long splicing wand from Brion Toss Yacht Riggers (briontoss.com). This fid enables the tapered rope end to be gripped by the wand and then pulled through the core, instead of pushing it in with a conventional fid and push bar. 

You need a very sharp blade to cut Dyneema. Regular household scissors will not cut even a single strand. I have found that the best way to cut this rope is with a box cutter (Stanley knife) fitted with a new blade. Here’s how to do the splice:

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splice tail
Step 1: The splice tail should be about 30 times longer than the diameter of the rope. The tail of ¼-inch rope should therefore be about 8 inches from the throat of the splice. Roger Hughes
tapered
Step 2: The tail is tapered by pulling out a pair of strands, about one-quarter of the way from the throat, then three more at roughly equal intervals. Do not cut these off yet. Roger Hughes
splicing wand
Step 3: The splicing wand is then pushed into the rope a little bit farther back from where the tail will end, then worked up inside the rope and out at the throat, where the tail will go into the splice. The tail end is then hooked through the thin rope loop on the wand and tightly locked with the knob in the handle. Roger Hughes
rope
Step 4: The splicing wand can now be eased back through the rope, pulling the tail with it. The pairs of strands can then be cut off flush, just as they enter the rope. Roger Hughes
wand
Step 5: When all the tail is embedded, the wand can be disconnected. Then, holding the neck of the splice, the rope is smoothed (milked) back from the splice, whereupon the end of the tail should vanish inside the rope. It’s as simple as that—but with one final operation. Roger Hughes
Dyneema
Step 6: Pull out a single strand of Dyneema from some spare rope, about 24 inches long. Then thread it into a stout needle, and lock-stitch tightly back along the rope from the throat to roughly where the first taper was; now stitch back again at 90 degrees to that stitch. Tie the two ends of the stitch together with a reef knot, then bury the ends in the rope. This lock-stitching is important because it prevents the splice from slipping under light loads. The strength of this type of splice increases dramatically as the outer cover contracts and grips the inner tail under load. Roger Hughes

It’s easy to become confused about the different manufacturers’ strength figures for Dyneema because they vary greatly with the construction and material. Once my splices were finished, I needed to know the strength of my new splices. After all, there’s not much point in having rope with a breaking strain of thousands of pounds if you don’t know what the weakest point is at either end.

Miami Cordage has a ­government-inspected and -calibrated rope-testing bed, about 40 feet long, on which they test the strengths of ropes for US Navy and Coast Guard vessels. Miami Cordage CEO Jason Hoffman kindly agreed to test one of my lifeline splices to destruction. 

I made an eye splice on both ends of some spare ¼-inch-­diameter Dyneema. This rope was attached to the machine, and I watched as it stretched the line well past 2,000 pounds. Finally, at an incredible 7,596 pounds, the actual rope snapped, yet both my splices held! That’s over 3 tons, and I have an official certificate to prove it. No wonder racing sailors love their Dyneema. Now, so do I.

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The test bed for all of Roger Hughes’ constant improvements is his 1977 Downeaster 45 schooner, Britannia.

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