I’m sure that most sailboat owners will have heard about the super-strong rope, known collectively under the trade-name Dyneema®, but sold under various names by rope-makers who weave the fibers into rope for marine use. The technical name is Ultra-high-molecular-weight-polyethylene (UHMWPE) - quite a mouthful. I didn’t know much about it either, or ever actually used it until I considered it as a substitute for the wire on my schooner’s worn-out lifelines, which needed replacing due to old-age and serious chafe.

Dyneema rope is considerably stronger, size-for-size, than double-braided rope, and also stronger than stainless wire of the same thickness. For example: 1/4”inch 7x7 stainless steel 316 wire has a tensile strength of about 4800 Lbs. The same thickness in double-braided line is roughly 4250 Lbs., but 12 strand single-braid Dyneema has an amazing tensile strength of between 8,000 and 12,000 Lbs. 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 now becomes a viable possibility.

Old-wiresNot only is Dyneema stronger than wire, it is also about six times lighter than the comparable thickness of 1x19 stainless wire, which is mostly used for standing rigging on sailboats. My old wire lifelines weighed 13 Lbs., and the same length of Dyneema rope weighed only 2.4 Lbs., saving a massive 10.6 Lbs.. Well it all helps, doesn't it? More interestingly, there is about 750 feet of 3/8”inch diameter wire rigging on Britannia which weighs 0.332 Lbs., per foot - that's a total of 249 Lbs. If I switched all of that for Dyneema, it would save approximately 220 Lbs. of high topside weight. Now that's significant!

Then there is the weight of many yards of running rigging on Britannia, with her square-sail on the foremast, and the extra lines required to control that sail, along with four other fore-and-aft sails.

What puts many sailboat owners off Dyneema is its price, which in most retail boating outlets is about twice that of comparable size double-braided rope. However, Miami Cordage Inc., is a rope maker hidden in the industrial depths of Miami, Florida, and considerably less than the regular retail outlets most boaters - including me - have previously paid. Most owners will not have heard of them, because nearly all their product goes to the United States Navy and Coast Guard, and other industrial outlets. Yet they make every conceivable type of rope, from old style three strand Manila to 12 strand Dyneema, which they call Ironlite, and they sell over the counter.

I discovered another significant benefit in using Dyneema, that is, the ease of which an eye-splice can be formed, unlike the complicated (at least for me) Class 1 reverse-tuck procedure, for splicing double-braided line.

Splicing-wandUnlike double-braided rope, twelve 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 rigging. This fid enables the tapered rope end to be gripped by the wand, then pulled through the core, instead of pushing it in with a conventional fid and push bar. With sixteen splices to make for my new lifelines, I was very thankful to have one of these neat tools, which can also be used for other rope-work.

                                                                                                 EYE-SPLICING DYNEEMA.

I used Miami Cordage 1/4”inch Dyneema for the lifelines, and for added appearance I used their solid blue color, which nicely matched Britannia’s Royal Blue topsides.

Note: You will need a very sharp blade to cut Dyneema. Regular household scissors will not cut even a single strand. I found the best way to cut this rope is with a box-cutter fitted with a new blade. Even with this I had to reverse the dull blade after making about five splices. Dyneema is tough stuff!

Stage1

Stage 1, The splice tail should be about 30 times longer than the diameter of the rope. The tail of 1/4”inch rope should therefore be about 8”inches, from the throat of the splice.


Stage2
Stage 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.



Stage3
Stage 3. The splicing wand is then pushed into the rope, a little bit further back from where the tail will end, then worked up inside the rope and out at the throat, where the tail is to 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.


Stage4
Stage 4. The splicing wand can now be eased back through the rope, pulling the tail with it. The pairs of strands should then be cut off flush, just as they enter the rope.



Stage5
Stage 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--except for one final important operation.


Stage6Stage 6. Pull out a single strand of Dyneema about 24”inches long from some spare rope, 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 slipping under light loads. The strength of this type of splice increases dramatically under load, as the outer cover constricts on the inner tail

Chafe on wiresStanchionsThe greatest problem with any rope is wear and tear, and weakening caused by chafe, and Dyneema is not invulnerable to this. Sheets often rub against lifelines and shrouds; rigging moves in spreaders; lifelines pass through stanchions; fenders are tied to lifelines; etc., all have a chafing effect on each other. However, one reason I chose Dyneema for my lifelines is because it is easily inspected for chafe, as opposed to the vinyl covered steel wire I had before, which had started to corrode from inside, without visible evidence on the outside. Where chafe is likely to occur, I fitted long plastic sheathing that clips loosely over the line and even rotates when rubbed with another line. This is easy to replace when any chafe becomes visible, long before it effects the Dyneema lifeline. If rainwater or sea spray gets into the cover it will not affect the rope, unlike wire.

Chafe-guardsIt's easy to become confused about the different manufacturers strength figures for Dyneema, because they vary quite a lot with the construction and material. I knew that every time a knot or splice was tied in a rope it weakened it, (surprisingly, splices are stronger than knots), sometimes by as much as 50% percent, but 50% percent of what? What I needed to know was the strength of my own new splices. After all, there's not much point having rope with a breaking strain of thousands of pounds, if you don't know what the weakest point is at either end.

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

Test-rigI made an eye splice on both ends of some spare 1/4’inch diameter Dyneema rope, then drove 230 miles to the factory in Miami. This rope was attached to the machine and I watched as it stretched the line well past 2,000 Lbs., It still held at 4,000 Lbs., when the rope was as tight as a steel bar. Then finally, at an incredible 7596 Lbs., the actual rope snapped, yet both my splices held! That's three and a quarter tons, and I have a Government official certificate to prove it!

I am now seriously thinking of changing some of Britannia’s standing rigging for Dyneema. My twin 59’foot long back-stays, the 15’ foot triatic and foremast running back-stays are not subject to chafe and would save about 58 Lbs., in high topside weight. From a rough calculation, that would be equivalent to 300 Lbs.of ballast. No wonder the racing boys love Dyneema!

 

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