Getting a Line on Cordage
Bernard Moitessier and Henry Wakelam were among the first cruising sailors to use rope made of synthetic fibers. In 1957, they scavenged serviceable yarns from nylon hawsers discarded by Cape Town whaling ships and twisted them into three-strand line to use as halyards and sheets. Although nylon was a vast improvement over the manila hemp to which they were accustomed, they wouldve been better off with one of todays high-strength, low-stretch fibers, which are vastly more suited to running rigging.
Nearly half a century down the line, the revolution in cordage technology continues to bring fiber products with greater strength and less stretch. None has durability to equal that of polyester under exposure to seawater and sunlight, but all have found a place, whether standing alone or blended with others, in the complex world of sailboat rigging.
Four principal characteristics define a ropes quality and purpose: durability, hand, strength, and stretch. Rope manufacturers can adjust their sophisticated processes to blend these traits in almost any desired combination so that a line can better fulfill a particular function aboard a cruising or racing boat.
Durability: Durability rates highly with cruising sailors. None of the other properties will be of much use if the line quickly deteriorates and becomes untrustworthy. The primary causes of deterioration are chafe and UV-ray degradation, and while chafe damage is usually visible, a simple inspection cant reveal damage caused at the molecular level by the UV components of sunlight.
Hand: Hand is the subjective characteristic of rope that relates to how it feels in the hand and how it handles. Hand is more or less important depending on the intended function of the rope. Sheets, because theyre handled constantly and need to run freely and flake smoothly, need to have a softer hand than halyards, which, in the cruising world, anyway, are often set and forgotten.
Strength: Next, a line needs to be strong enough to handle the loads, both static and dynamic (shock), that it will encounter in normal operation. The great advances in synthetic fibers have led to the creation of ropes with strengths many times greater than those of the natural fibers—hemp, sisal, and linen—employed before about 1950.
As rope diameters continue to shrink with no loss in strength, smaller sizes are able to handle the same tasks. Big boats reap great benefits because the high-strength lines are not only much lighter than their forebears but also have smaller diameters, which adapt more successfully to sheaves and winch drums.
On smaller boats, halyards and sheets of appropriate strength can be too small for comfortable handling. Manufacturers counter this differently in double-braid line than they do in single-braid. To give double-braid line a comfortable hand, they wrap a lightweight, bulky cover around a high-strength, load-carrying core. When making single-braid ropes, they blend the high-modulus (high-strength/low-elasticity) fiber with a bulkier, low-modulus one to make them thicker.
Stretch: In moderation, stretch can be desirable, but at times its not wanted. For halyards, especially, stretch is counterproductive. If a halyard stretches in a gust, the sail will become fuller and generate more heeling moment. This is why stainless-steel wire and those infernal reel halyard winches, with their erratic friction brakes, were once common and can still be found on older boats that havent been rerigged. Jib sheets and mainsheets, on the other hand, need to stretch to absorb the impact of gusts and occasional unintentional jibes. Rope manufacturers can tailor the degree of stretch with their selection of fibers and the manner in which they lay or braid them.
|After stripping the cover off the working part of a halyard to save weight aloft, Chien Noir proprietor Cédric Chauvaud prepares to secure the remaining cover.
All these characteristics—in combinations appropriate for almost any use—are available in polyester, which should satisfy the needs of any cruiser looking for long life at low cash outlay. On many cruising boats, high-performance, low-stretch double-braids serve well as halyards, preventers, and spinnaker guys, and a single-braid, because of its suppleness, will make excellent sheets and roller-furling lines. Either construction is useful for control lines like vangs and outhauls.
Upping the Modulus
Other synthetic fibers used in marine rope making include ultra-high-molecular-weight polyethylene or UHMPE (Spectra, Dyneema), para-aramid (Kevlar, Twaron, Technora), polyester-polyarylate (Vectran), and, for the truly exotic, PBO, which stands for poly-paraphenylene-2 6-benzobisoxazole (Zylon). These all exhibit much higher tensile strength and lower stretch than polyester and, in varying degrees, lower resistance to UV degradation. Thus, theyre most useful in cruising boats when combined with other materials that protect them from exposure to sunlight.
PBO: PBO has the highest tensile strength and elasticity modulus. Its used for standing rigging on high-tech boats like the Open class singlehanders and for halyards on one-designs and other high-performance racers. But it needs to be protected both from UV and chafe. For standing rigging, this is often done with a shrink-on black-plastic cover. Even when so armored against abuse, its far lighter than stainless-steel rod rigging. Cost and upkeep, though, effectively eliminate PBO from the cruisers range of choices.
UHMPE: Manufactured from the next strongest fiber, UHMPE ropes have characteristics that make them more applicable to cruising-boat requirements than those made with the other synthetic fibers. According to the Cordage Institute, UHMPE has "excellent" abrasion resistance, a function of a low interfiber coefficient of friction. It therefore adapts to running over sheaves more readily than do aramids and PBO.
When coated during manufacture, it has reasonable resistance to UV degradation, but for long-term exposure, its best when protected with a polyester cover.
Halyards are often made from double-braid lines with braided Spectra or Dyneema cores. The polyester cover is stripped off the standing part of the halyard, back though the area usually held in the line stopper, and left on for hand where the line is handled. Unprotected UHMPE braids are useful for lines that spend much of their lives in lockers, like the sheet for the asymmetrical spinnaker or drifter. Their light weight is a bonus in light air and makes them easy to carry. Spectra is widely used for mooring warps aboard large yachts and commercial vessels because the smaller diameters its tenacity permits are easier to manhandle than wire rope or polyester and nylon cordage of similar strength.
Para-aramids: These are less functional aboard cruising boats because they generally have only moderate abrasion resistance, which leads to faster breakdown when used over sheaves. Technora, the exception in this group, has higher "dynamic durability," as the Samson literature puts it, and handles turning around sheaves better than its sisters, Kevlar and Twaron.
On some bigger, high-performance cruising boats, para-aramids are used for the standing parts of running backstays. As with PBO and Vectran, theyre usually sheathed in black plastic.
Polyester-polyarylate: We will refer to polyester-polyarylate as Vectran since thats the only brand used in marine rope. Vectrans strength is similar to that of the aramids but with much better abrasion resistance, so it lasts longer when run through blocks. Vectran shares with PBO the Cordage Institutes "very low" rating for creep, meaning it doesnt elongate gradually when held under tension for long periods of time.
Chien Noir (Black Dog), the gang of French riggers used by many Open 60 skippers, makes extensive use of Vectran strands for lashings. When combined with a polyester cover, Vectran can fulfill most jobs on high-tech racing boats, and it also can be useful on cruisers.
For example, New England Ropes Sta-Set X Plus combines a unidirectional (not twisted or braided) Vectran core, bulked up with multifilament polypropylene, inside a braided polyester cover. The low-stretch and low-creep characteristics of the Vectran make this a good halyard material. The cover both protects the core and gives the finished rope a nice hand.
Looking back over the past three decades, remarkable advances have been made in rope and fiber technology. However, in the new-millennium world of cordage, theres no panacea, no do-everything line that cruising sailors can trust to last forever.
Though now furnished with far better tools than ever before, the prudent mariner must still pay close attention to the old enemies of rope—age and chafe—while adapting new skills and applications to get the best out of the current crop of fibers.
And while the cruising sailor can still get by with polyester for his daily thread, a little seasoning with higher-modulus fiber will help keep his sails and rig in better shape for sea.
In next months Hands on Sailor section, Jeremy McGeary, a CW associate editor, will discuss techniques for employing high-tech ropes.