Rope is a critical component to any sail handling system on an ocean voyaging boat. Even with elaborate mechanical and hydraulic help, there are few, if any, boats that don’t rely on some type of line to control the hoisting, trimming, or furling of sails. Choosing the right line for the job can mean better and safer sail handling, better conversion of wind energy to propulsion, and greater useful life of the line for its task.
There are several important qualities we can look at in evaluating line. These include low stretch, flexibility, strength, ultraviolet longevity, abrasion resistance, and, for most users, low cost. Low stretch is important in most applications so as to minimize energy loss and maintain control in sail shaping. Flexibility, while a seemingly obvious trait for line, is not so for some materials, and can also be greatly influenced by the construction method. Line strength and ultraviolet (UV) stability are probably the two traits most dependent on material used rather than on the construction method. All other factors being equal, abrasion and chafe resistance is for most users the single most important trait determining a line’s useful life. And, finally, the useful characteristics of each line must be weighed against its cost. While no line is superior in all these qualities, line manufacturers offer many products that combine various traits in line types ideally suited for specific tasks.
Through increased technological development of both line material and construction methods, rope is being used in lieu of stainless and galvanized wire at an ever-increasing rate. The increased strength, lighter weight, and durability of modern line have helped improve sailboat performance by reducing weight aloft and parasitic stretch in sail control, and have made line handling in general easier and safer for the crew. In fact, the strength characteristics of some materials are so impressive that line, rather than wire or rod, is even being used in some less-critical standing rigging applications, such as running backstays and checkstays. Currently, however, the use of fiber for standing rigging is strictly in its developmental phase and will not see widespread use for some years to come. This is particularly true for ocean voyaging yachts, where durability and reliability are of paramount importance.
In order to determine the ideal line to employ, it’s useful to review the task we’re asking the line to perform. For sail handling, the lines that directly act on the sail should have the lowest stretch so as to minimize the loss of energy between the wind and the boat. These lines include halyards, sheets, and afterguys and are usually rigged without purchase systems so the line acts as the direct load conduit. The line must be easily handled, and so must be of a manageable size to match its strength and stretch characteristics. Another important trait, particularly for the ocean voyaging yacht, is resistance to chafe, particularly for lines like halyards that are difficult to access and inspect when in use.
Secondary control lines, such as outhauls, cunninghams, lead adjusters, traveler lines, vangs, foreguys, and reef lines, are usually rigged through some sort of purchase system, have less load, and thus need not be low stretch. Because they are usually handled less than sheets, guys, and halyards, and are usually anchored directly to cleats or jammers, they can be smaller in size. However, their infrequent use usually means they are inspected and replaced less than other lines, and thus they should have good UV stability to prolong their useful life.
If this review were written at any time until about 30 years ago, the list of qualities above would have included resistance to rot, an important factor for organic fibers such as hemp, cotton, and sisal, which were used for centuries in making line. Line made from organic fibers had to be carefully tended to minimize rot and prolong their productive life, with this care producing serious limitations on use. The advent of synthetic materials in all modern line has made this rot factor no longer relevant, and line can take a significant amount of abuse relative to organic line. It is significant to note, however, that while biologically induced rot may no longer be applicable, degradation from the UV rays in sunlight in some cases has replaced it as another form of line rot.
Another important aspect of synthetic line fibers is their performance consistency relative to organics, which could vary widely in strength and stretch depending on not only the type of material used but the manufacturer and method of construction. The variations seen in modern line have less to do with intrinsic differences within the fiber types than in manufacturing method.
There are several fiber types in current use by marine rope manufacturers, each having their own qualities of strength, stretch, flexibility, chafe and UV resistance, and relative cost.
· Nylon: The granddaddy of synthetic fibers, nylon’s high strength and elongation characteristics make it ideal for applications where strength while under dynamic loading is desired. These include anchor, tow, mooring, and dock lines, or anywhere a vessel needs to be secured. Depending on the braid type, nylon lines will elongate from 20% to 40% of their breaking strength, and thus have tremendous capacity to absorb the potential dangerous energy accumulated by shock loading. It can be dyed into many colors.
· Polyester: Dacron is the name given by DuPont for its polyester fiber, and is the most widely used by cordage manufacturers. AlliedSignal also provides a variety of polyester fibers, and in Europe it can be found under the name Terylene. In the early days of synthetic rope development, polyester replaced nylon by having equivalent strength, lower elasticity, and greater abrasion resistance, for about another 15% in added weight. With these qualities combined with low-cost, it is the most widely used fiber in marine rope today and is priced to provide a cost-effective solution to most running rigging applications. It is commonly used as both core and cover material on double-braided line, can be dyed many colors, and is sometimes offered in soft, easily handled yarns.
· Polypropylene: This fiber is very lightweight and can float on water, and thus is used in many safety line applications. It stretches about the same degree as polyester but has only 60% of the overall strength. Because of its low melting point, polypropylene melts easily if subjected to the frictional heat generated by releasing lines under high loads. It also has relatively low UV resistance; thus the fiber easily degrades under extended exposure to sunlight. Like polyester, it can also be dyed many colors, and is used as a lightweight cover material for neutrally buoyant line.
· Spectra: This is a high-modulus polyethylene (HMPE) fiber made by Allied Signal Technologies, with an analog in Europe known as Dyneema. This fiber is significant in having the highest strength-to-weight ratio of any synthetic or natural fiber, nearing 10 times that of steel. It also has a remarkable combination of properties in having very low elasticity, light weight, and excellent abrasion resistance and flex-fatigue life. Being of the same chemical family as polypropylene, it also has a low melting point and no water absorption, and it floats on water. Yet, unlike its cousin, Spectra also has excellent UV stability. A drawback to the use of Spectra in high-load applications is its tendency to creep, a property of slight elongation from fiber deformation due to molecular slippage while under a constant static load. The effect is usually, however, only a few percent at loads approaching those 85% of the breaking strength. Spectra is a white, very fine filament fiber, which is usually coated with dyed urethane to keep the fiber bundles intact without fraying and aid in reducing slippage between the core and cover materials.
·Kevlar: Another fiber manufactured by DuPont and known for its diverse applications where high strength and light weight are required. It is a yellow aramid fiber and has the lowest stretch of any synthetic made. Drawbacks to its use are in its susceptibility to UV degradation and its low flex-fatigue strength, requiring 20:1 sheave-to-rope diameter ratios on blocks where Kevlar line is used under load. It has a tendency to abrade itself and is susceptible to failure if improperly spliced or knotted. Because of this property, cordage manufacturers try to minimize inter-fiber chafe in rope cores by coating fibers to facilitate slippage, or by blending core materials with other fibers. Kevlar also readily absorbs water, adding significant weight to the line when wet. Because of its strength, all aramid fibers are also very difficult to cut and will dull tools easily. These fibers have very high melting points, which makes them nearly impossible to burn. With the advent of other suitable fibers, use of Kevlar in line is on the decline.
· Technora: A black aramid fiber which improves on the qualities of Kevlar. It is stronger and slightly lighter in weight, but its most distinguishing feature compared with Kevlar is in having three times the flex-fatigue strength, allowing it to retain its strength over conventional sheave-to-rope diameter ratios of 8:1. Like all aramids, it has limited UV stability, but has lower water absorption than Kevlar.
· Vectran: Hoechst Celanese manufactures this fiber made of liquid crystal polymer, which made its sailing debut in the last America’s Cup. Vectran combines the best qualities of the aramids with those of Spectra by being more tolerant of bending than any other high-modulus fiber (six times that of aramids) while not creeping at critical loads. It is yellow-green in color, is hydrophobic like Spectra, and has a limited degree of UV stability yet a high melting temperature. Vectran’s weight is similar to that of the aramids, yet it is 30% stronger and performs up to 12 times better in abrasion resistance. The only downside of Vectran is its cost, which is currently about 50% higher than Spectra and more than twice that of Kevlar. Blending the fibers with others is a strategy used to achieve its superior qualities at lower cost.
The character of a line is as strongly influenced by how it is made as by the material used. The construction style governs not only important handling characteristics of the line, such as its resistance to kinking, hockling, and excessive wear and ease of splicing, but also its essential properties of strength and elongation.
In general, there are five basic styles of rope construction, each with its own best use on an ocean voyaging yacht.
· Three-strand: This is the simplest and most traditional type of rope, which is made by twisting fibers into yarns and the yarns in turn into strands, which are then combined, twisted in groups of three to form the rope. Since this construction method is very hard on the fibers, its efficiency for converting the inherent strength of the fiber into strength in the line is the lowest of any form, though it is the lowest in price and easy to splice.
· Plaited: Strands are woven singly or in groups of two to form a line that is high in energy absorption, nearly 75% higher than three-strand and 85% higher than double braids. This feature combined with it being non-rotational and resistant to kinking makes plaited line ideal for applications where high strength yet elasticity are important, such as in anchor, mooring, and tow lines. Plaited lines are easily spliced.
· Single-braid: Similar in appearance to plaited lines, single braids feature strand counts of 8, 12, or 16 braided in groups of two to produce a line that is easy to splice, soft to handle, and highly resistant to kinking or hockling. This latter feature is important for multi-part tackle systems, where lines must run freely through the blocks without snagging. This characteristic also makes them ideal for use in roller-furling systems and other low-load control line applications.
· Double-braid: This line is essentially two types combined, with a core of single-braided line that carries most of the load, shielded from wear and abrasion by a braided cover. This two-part construction allows for different fiber materials to be used to optimize the best characteristics of each. For example, many cordage manufacturers will cover a braided core of aramid fiber with a braided cover of polyester, allowing the strong core fibers to be protected from abrasion and UV exposure. This line type is generally firmer than single braids and thus is more prone to kinking, though it is usually lower stretch. Extension under load is minimized when manufacturers lay fibers in continuous filaments at low angles to resist inner-yarn abrasion and minimize flex-fatigue. It is probably the most common line type in use today aboard ocean sailing yachts, for common high-load sail handling applications such as sheets, guys, and halyards. It has been designed and refined by manufacturers to endure the rigors that jam and cam cleats, line stoppers, and rope clutches impose on line.
· Parallel-core: With little or no twist, the fibers in parallel-cored lines align more directly with the load and thus have very low stretch. These core fibers are sheathed by a braided cover and thus like double-braided line have the option of utilizing the best features of dissimilar materials in one rope. While parallel core lines are extremely strong when loaded in a straight line, this type of line is stiff (making it susceptible to kinking) and is difficult to splice. Parallel-core is also prone to strength loss during bending (this takes place when, over a given radius, the outside fibers within the core experience more tensile load than the inner fibers). Many Kevlar-cored lines are constructed with parallel cores and are used in low-stretch, high-load applications such as halyards and afterguys.
It is important to note that the tabulated values of line breaking strengths are not only a function of both fiber type and size but also construction style, and thus are specific to that particular line. Double-braided Spectra line with a braided polyester cover, for example, varies in its tabulated average breaking strength by up to 40% depending on the manufacturer. Even the strength values of a particular line will typically vary within a range of +/- 20%, and thus safe working loads are usually fixed at one-fifth of the average breaking strength and are based on static or moderately dynamic lifting and pulling operations.
It is also very important to specify a line for an application that not only meets its theoretical strength requirements, but is also used in such manner so this strength is not compromised. For example, wherever possible lines should be spliced and not knotted, as knots can compromise rope strength by as much as 60%. While this is clearly impractical in all cases, it should be strongly considered in such critical high-load applications as tow lines, halyards, sheets, and guys for which sudden line failure could be disastrous. If unfamiliar or uncomfortable with splicing, the user should in all cases consult a qualified professional rigger, as different line types require different splicing techniques. According to Tom Wohlgemuth of Chesapeake Rigging in Annapolis, an improper splice can seriously compromise the line’s strength, whereas the right splice as specified by the manufacturer will retain most of the line’s rated strength.
Abrasion or any other physical disruption of the fibers within a line should also be avoided by routing rigging to minimize chafe. Some fibers are also susceptible to significant strength loss due to excessive exposure to UV from sunlight. Aramids such as Kevlar will exhibit signs of UV degradation by discoloration and the presence of splinters and slivers on the line’s surface.
Some fiber types are better than others at retaining strength over time. According to Richard Hildebrand of Yale Cordage, empirical tests of several of their products have shown a slow degradation in strength when subjected to continuous use over a time scale of hundreds of hours. The reduction in strength reaches, then holds, at values as low as 50%, with Vectran showing the best performance, holding steady at 70%. These results corroborate with on-board tests made by Hall Rigging of Bristol, R.I.
And while more resistant than organics, all synthetic fibers are also subject to damage by exposure to solvents, acids, and alkalies. This includes fumes as well as liquid form, and should be avoided whenever possible.
Hildebrand also points out that probably the most under-recognized factor in line strength is dynamic loading. Whenever a sudden load is put on a line, such as when slack is being taken up suddenly until the line is drawn taut, a dynamic or shock load is imposed that can exceed the static strength of the line. These instantaneous changes in load will increase the more rapidly the actions occur, and can, in extreme cases, reach several times the normal static load. Lines made of low-stretch materials such as aramids are more susceptible than lines made from high-stretch materials such as nylon, and since actual elongation is a percentage of length, shorter lines are more prone to this effect than long ones.
The proper choice of line for a particular task will be made after an optimized match between factors of line performance and cost, which for each boat may be a unique solution. As shown above, there are applications for which the use of a superior line, such as double-braided Vectran, for every sail handling operation is not just cost-prohibitive, but impractical given other options. Often the choice of line is made as a compromise choice between waiting to order the absolutely right line and simply selecting something that is readily available from a local source. As with any system on the ocean voyaging yacht, consultation with a professional is recommended to help determine the best use of the appropriate line from the range of options.
In general, voyaging sailors will tend to emphasize low cost over low stretch, since the choice of a high-tech line may easily outperform other elements of their sail-handling systems. Longevity and durability are important factors, again because of the prohibitive cost of constant replacement. Easy handling and spliceability can also be important, especially for those outside the reach of professional rigging assistance. Without the pressure of competition, color-coding lines for fast identification is also of secondary importance, although for some line color and style will have aesthetic significance, particularly for traditional craft.
Racing sailors, both offshore and inshore, will make the most demands of line, pushing it to its functional limits. The new breed of high-modulus fibers allows for line that is substantially smaller than previously used, and on boats less than 40 feet the loads are easily accommodated by line that is often too small to be comfortably handled. This has the twin benefits of not only light weight, but also lower cost as lines get smaller. In applications such as halyards, low stretch is critical, with figures that exceed 1% considered unacceptable due to the profound effect this can have on sail shape. (If this sounds absurd, consider that 1% of the 50-foot length of a 40-footer’s jib halyard is six inches, a virtual mile considering the sails have negligible stretch and are sensitive to shape induced by halyard tension.) With fewer winches and more jammers, color selection becomes important to separate lines led into the companionway or cockpit.
The use of lightweight lines in both voyaging and racing yachts increases performance for both by reducing weight aloft, which increases righting moment while reducing pitch gyradius. Halyards, afterguys, and spinnaker sheets made of Spectra or Vectran are now commonly stripped of their cover materials beyond where handled by hands, winches, or cleats, so as to reduce weight and water absorption even further. The braided core is exposed to UV, chafe, and abrasion, but is usually inspected regularly and replaced often enough to not fail when in use.
The advent of several different synthetic fibers has combined with advanced construction styles to produce marine ropes that are vastly superior to their organic predecessors. These lines have varying relative properties of strength, elasticity, abrasion and UV resistance, ease in handling, and cost which must be weighed in order to match them with their task to perform on the ocean voyaging yacht. Low-stretch types are desirable for use in halyards, sheets, and guys, while a little stretch can be permitted for sail control lines. Tow, mooring, and other vessel control lines must have some stretch in both material and design. And while strength and low-stretch is desirable in most applications, dynamic loading can seriously compromise the integrity of the line and in extreme cases result in its catastrophic failure. For this reason, working strengths should be heeded whenever possible to avoid overloading due to shock loading.
Voyaging sailors tend to accept a compromise between low-stretch and low-cost, preferring lines that are more durable, easier to splice, and less prone to kinking than the low-stretch, high-modulus lines used by racers. Besides being low stretch, racing line must also be durable enough to withstand abuse from cam and jam cleats, line stoppers, and rope clutches, all of which tend to severely distort the line while under high loads.
Dobbs Davis is a freelance marine writer and U.S. editor of the British sail racing magazine Seahorse.