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High-Modulus Rope and the Marlingspike Sailor

This piece is a slightly altered version of an address to a meeting of the Pacific America's Branch (PAB) of the International Guild of Knot Tyers.

A few years ago, I had the pleasure of addressing the PAB on the subject of high-modulus ropes. The remarkable materials that go into these ropes are at least twice as strong as conventional fibers like Nylon and Dacron, and these in turn are twice as strong as plant fibers like Manila and hemp. Without question we are seeing some powerful evolution here, and in my previous presentation I addressed some of the benefits and challenges of HM rope.

A great deal of further evolution has occured in the few intervening years, and this fact is almost as significant as the substance of the changes. That is, rate of change is a phenomenon in and of itself, a thing we need to deal with, along with matters of technical substance.

So tonight I wish to talk about high-modulus rope, its uses, challenges, and potential, but also how we relate to it, how we can incorporate this remarkable stuff into the web of engineering efficiency, gracefulness, economy, and the intuitive "rightness" that we call tradition.

Let's start with the challenges. In the years since that first talk, hundreds of destruction tests, and quite a few in-the-field failures, have confirmed a central truth: HM doesn't like knots. Although fantastically strong in tension, HM fibers are quite weak in compression. Since knots invariably compress the rope under load, it is clear why knots typically weaken HM rope by at least 70%. And it gets worse: HM rope also tends to be quite slick, so slick that long-trusted knots like the Bowline will crawl right out under loads as low as 10% of ultimate strength. We've even seen cases where the (non-structural) cover of an HM rope broke at low loads, allowing the core to slide right out, leaving the still-knotted cover behind like an empty snakeskin.

This is not an overwhelming drawback; wire doesn't like knots, either. But HM rope is, well, ROPE, and all of our expectations, conditioning, and intuitive inclinations tell us that we should be able to tie knots in the stuff. Instead, we have to reconfigure our most basic ideas about a profound, archetypal tool. To make matters even worse, this newly-reappraised tool exists side-by-side with other rope, of half the strength or less, radically more elasticity, and radically lower price. It's as though, 50 years ago, we were suddenly confronted with an entirely new kind of horse, that looked just like a normal horse, but could run twice as fast. And then, even more recently, we found a horse that could run four times as fast as the original one, but couldn't turn left. All 3 of these horses might look more or less the same, and the latter 2 would appear identical to the casual observer. No problem unless you were sitting on the wrong horse when you needed to turn left...

A related challenge is the matter of scantlings; rope of a certain size simply looks right for a job, based on experience and/or the practices of those whose opinions we respect. In the absence of detailed testing for every application, a considered, carefully-developed visual sense of what is appropriate is a good basis for materials selection. The problem is that a considered, carefully-developed visual sense of what is appropriate takes time to develop, takes the kind of experience, familiarity, and long-term use that rapid development of materials, constructions, and applications tends to preclude. So we are in the process of recalibrating our judgement, and that takes time and effort. A useful saying here is, "Good judgement is based on experience, which is based on bad judgement."

This issue has cropped up before, notably in the mid-19th century, as rope standing rigging was rapidly and decisively displaced by iron. Think of it: a material that, with trivial variations, had defined rigging for thousands of years suddenly rendered obsolete by one that was far stronger for its size, plus being less susceptible to decay. And then, just a few years later, it was iron's turn to be displaced by steel, which was at least 30% stronger still.

There are some people who never got over this 1-2 punch, and to this day, 150 years later, you can still find steel rigs being built to iron scantlings in traditional craft. Now, cautious, conservative adaptation is a good thing, but what does it bode for us today if we are still catching up on changes from the 1850's?

One more challenge is what might be called the technical interface: how rope interacts with machinery like stoppers, winches, sheaves, human hands, wind, sails, masts, towers, drogues, etc. The most immediate problem here is that HM rope is so much smaller. Aside from the psychological challenge mentioned above, there are simple mechanical difficulties. What are the ideal sheave diameters and tread profiles? How can a clutch stopper, or even a cleat, generate sufficient friction without crushing or tearing the rope? How can one release loads quickly, without melting the rope? For halyards, when the load is at full hoist, is there any alternative to having a great deal of incredibly strong, tough, inelastic -- and very expensive -- rope sitting on the deck doing nothing? And how do you hang onto this stuff, anyway?

Taking these few questions in order:

Sheave Diameters and Tread Profiles
If you scale the rope to the block strength, you will usually end up with a generous sheave diameter. This is because HM is much stronger than Dacron, and most block sheaves are scaled to Dacron. Since the right strength HM line will be smaller than a similar-strength Dacron line, the relative diameter of the sheave will be greater. But in case you get a block designed for HM line, be sure the sheave diameter is at least four to six times greater than the rope diameter.

Tread profiles can be the usual semicircular profile, but V-sections are at least as good, as they support small rope on a greater arc. Kevlar is an exception here; it is extremely sensitive to tight turns, and will fatigue and break over sheaves that every other HM rope is quite happy with. Special Kevlar sheaves, with extra large diameters and a wide, flat tread profile will help, but not a lot. That's why you don't see Kevlar halyards much any more.

Clutches and Cleats
Although a too-small cleat or clutch could, like a knot, weaken HM line with excessive compression, the problem is fairly self-solving; even a relatively moderate load could rip the thing out of the deck. The real problem is how to grip HM line so that it doesn't slip through the belay. With cleats, this means careful, fair-led belays, with extra turns. With clutches it means various ways of fattening the rope for more grippable area. Some rope-preserving ploys include:

a) artfully, cleverly inserting a short "fattener" inside the core in the way of the stopper,
b) "building up" the rope, in the portions that need to be handled, stoppered, run over a sheave, etc., by splicinq it, in a variety of ingenious ways, to a fatter rope;
c) making the whole rope ridiculously large, way stronger than it could conceivably need to be, resulting in excess weight (that largely cancels HM's advantages), at an unbelievably higher expense, and, post-hoist, having a huge pile of this very expensive rope sitting on deck, doing nothing.

Most people take option "C".

Melting
Slacking a line under load -- think mainsheets and running backstay tackles -- has taken on a whole new meaning with HM rope. The loads are so high, and concentrated on such a small area of rope, that the braided cover can easily heat up and melt, at least in racing craft.

In recreational and industrial pursuits. Dacron covers are being displaced by Nomex, Kevlar, Vectran, and other high-melting-point fibers, singly or in blends. These fibers also tend to be very abrasion-resistant. And expensive. So the work for riggers is to reduce the friction that is the major cause of heat (By the way, firefighters have a related problem, but with direct heat instead of friction-induced heat).

So the technical interface, the materials' properties, and the psychological variables are all at work here, as we figure out how to deal with this stuff. My concern is: how can we address all 3, in such a way that we are not still employing option "C", or other undesirable options, into the 22nd century.

I would suggest that human experience and perception, mechanical configurations, and the rope itself are all aspects of a system, a system which also includes the nature and magnitude of the work, the time budget, money budget, factor of safety, aesthetic considerations, etc. High-modulus rope represents only a small part of the real challenge, that this influx of new materials, far from being the dominant factor, is more like a few words added to a vast and complex language. If we study the language of rigging, we will illuminate the individual words; if we study just the words, we become lost in rote-learned, disconnected details.

So how to study this language? Let me tell you a story: I recently visited New England Rope's factory in Fall River, Mass. It is a fine facility, with shiny modern machines, but way in the back and off to one side there is a hundred-year-old artifact, turning out lariat rope. Now lariat rope comes in a variety of lays, varying from extremely stiff to unimaginably stiff. This is because twisting the rope tighter makes it abrasion-resistant, makes it able to stretch appropriately under shock loads, and keeps the thrown loop from collapsing en route to the target. Very specialized stuff, for an ancient job.

Not far away from the lariat-making machine is a shiny new German-made machine weaving a cover onto some extremely low-stretch, high-load Vectran. This cover will never need to take any significant tension load; it exists to protect the core from UV --- and from chafe. So each yarn is twisted like a mini lariat, so it's tough enough. Stretch doesn't matter, and stiffness isn't excessive in this construction. Clearly, ropemakers didn't have to invent jacket-toughening concepts from scratch; those concepts help form the ancient grammar of rigging.

Similarly, selvagee strops have been reborn as parallel fiber ropes and slings, deadeyes are making a comeback in aluminum, and ancient knots are finding new homes in unprecedented applications. In short, our database of hard-won traditional knowledge was not vaporized by technological advance; it has just found new materials and applications to express itself through. So while it's all well and good to study and teach specific knots and splices, it might be at least as useful, in the long run, to study concepts, to note the reasoning behind the myriad of traditional details. If we are equipped with the same reasoning that informed those details, we are more likely to go down a workable path, instead of making stuff up or leaving stuff out.

Even the traditionalist's reluctance to accept change can be seen as a positive thing, as it means that we are less likely to embrace flawed 'fixes'.

For example, I mentioned Kevlar earlier. Here is a fabulously strong, light, inelastic, and hard-to-melt plastic. At the time of its introduction, it seemed like the perfect halyard material, so sailors started putting it to use. In short order the halyards broke, right at the sheave (see above). By standing back, by being traditionally cautious, the majority of sailors saved themselves a lot of grief with Kevlar. "Let the racers break this newfangled stuff" was the byword, the same byword muttered for centuries no doubt, as racers tried out rope instead of vines, lead ballast instead of bags of sand, aluminum masts instead of wooden ones, travelers, vangs, and all that other stuff instead of whatever we'd been using before. By hanging back, we let someone else pay for the R&D. The trick is to participate in the R&D, to help our overeager fellows see how time-tested ideas can make this newfangled stuff work. And in doing so we familiarize ourselves with the new stuff, so we are likely to take less than a century to accept it. Then everybody wins.

This brings me around, at last, to the ostensible subject of this talk: how High-Modulus rope is displacing wire in rigging. It is already happening, with race boats leading the way. And once again traditionalists are hanging back. Don't they get it? We're talking about rope here! We're talking about splicing and leathering and seizing, deadeyes, lanyards, doing cool stuff with fids and roping palms. We are probably witnessing the beginning of the end of an anomalous, 150-year reign of wire rope. Oh, wire won't go away altogether, I suspect, but will play a different smaller role in all aspects of rigging. The point is that we can hasten the change; racers have already done enough of the initial foolhardy materials trashing to establish reliable guidelines on materials behavior and load variations. It's time for us to step in, to save these poor souls from themselves. Long live the marlingspike.

Fair leads,
Brion Toss