12-08-2004
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Join Date: Jan 2000
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Understanding Cordage
This article was originally published on SailNet in August 2001. These days sailors, benefiting from the advances in chemistry and rope-making technology over the past 10 years, can choose from a bewildering array of lines. The right choice of cordage for each application on board any boat involves numerous factors. The main concerns are: strength, stretch, longevity, cost, ease and strength of knotting and splicing, ability to work on winches and windlasses, and kindness to the hands. But to keep your choosing manageable, these considerations can be reduced to a discussion of the two main factors that influence the use of line: the construction method and the materials used to build the line. Construction There are three main methods of machining individual threads into strands (called yarns) and thence into rope (or what most sailors refer to as line). Each method has its advantages and disadvantages. Here's a quick digest of what you'll need to know to assess your needs and better understand the choices available. - Three-strand twist is an old favorite. It is inexpensive to produce but allows the greatest possible amount of stretch. In some materials, three-strand line is capable of elongating nearly half again its relaxed length before breaking. Splicing three-strand is easy and quick. These attributes make it ideal for use as anchoring, docking, and mooring lines where stretch is kind to deck hardware. Three-strand line can become stiff with age, rendering it difficult to knot and coil properly.
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- Single-braided line, sometimes called plait, waxes and wanes in popularity. It has less stretch than three-strand and is more expensive to produce. Single braids have a supple feel and remain easy to coil and store. They are kinder to the hands and work better in self-tailing winches than three-strand line. However, single braid lines are difficult to splice well.
- Double braids have the least amount of stretch and make up the bulk of all running rigging used aboard contemporary sailboats. A braided core is covered with a braided sheath, either of the same or a different material. The core, or inner part, can effectively be made of a blend of materials to take advantage of differing properties. It can be woven at low angles, and even laid up as parallel fibers to reduce stretch. Double braids offer the choice of a smooth or fuzzy cover. Most are easy on sailors' hands and provide excellent grip in self-tailing winches and clutches. Double braid is more expensive to build and takes some practice to splice correctly. The cover can be woven with a multitude of colors for easy identification.
Materials The fibers are of equal importance in choosing a line to suit a job on board. All fibers on the market these days are synthetic with trademarked names from chemical companies. And each fiber has special characteristics that make it well-suited to particular tasks. | 
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- Nylon has high strength and very high stretch, making it an obvious choice for docking, anchoring and mooring lines. There are various grades and coatings for nylon with widely different reactions to water, UV, chemicals, and aging. Premium-grade, continuous-length fiber cordage is more expensive, but has a much longer life span. Since nylon loses strength when it's wet, larger-diameter line should be used than most strength charts indicate. Nylon line does not stand up well to chafe and must be protected from sharp objects. Nylon can also shrink with age, becoming stiff and unmanageable.
- Polyester, most often in the form of Dacron, makes up the bulk of all running rigging for good reason. Dacron is a very moderate fiber: It is fairly strong, has little stretch, is reasonably abrasion-resistant, not terribly expensive, has good UV and chemical resistance, and is easy to dye in multiple colors.
- Kevlar and aramid fibers are stronger than steel by weight and have almost no stretch. However, they do not bend well and require oversize sheaves. As a core material in double braids, they tend to cut through a polyester cover. Aramid lines are extremely difficult to splice and remain quite pricey.
- Olefin, polypropylene, and other olefinic fibers areextremely light for their strength and stretch—in fact they float and do not absorb water. Sensitive to UV, double-braided lines with olefinic covers must not be left in the sun. In addition, they are heat sensitive and melt if run rapidly over a winch.
- Spectra, Vectran Liquid Crystal Polymer (LCP), Technora and several other fibers are very strong and have low stretch. Each has its own advantages but all are relatively expensive. They are quite often blended together, sometimes with polyester or an aramid in the cores of double braid.
Suggested Reading: Hold That Line by Tom Wood Quick Rig and Deck Check by Tom Wood Adjustable Sheet Leads by Brian Hancock
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