Has your line knowledge kept up with advancements in materials and construction methods?
Be you a rag-bagger or stink-potter, a common thread joins all boat owners: rope. The quality and variety of rope available is constantly evolving and growing, so it’s more important than ever to be able to choose the right rope for a particular job. Despite the seemingly endless number of polysyllabic words that rope manufacturers use to describe their products, selecting the right one boils down to three things:
- Method of construction
- What exactly it is you want the rope to do
Rope is the generic term for cordage more than 1 inch in circumference, while smaller stuff is known as cord, twine, line or string. Finer still is thread and double yarn.
Rope is commonly used to describe bulk material, such as a spool of rope at the chandlery, while line is generally defined as rope cut from said spool and used for a specific task on board, such as a spring line. For the purpose of this article, the terms rope and line are interchangeable.
Most lines found aboard boats today are made of synthetic fibers such as nylon, polyester and polypropylene, compared to 40 years ago when organics such as hemp, sisal and cotton ruled the waves. Synthetic lines have numerous advantages over their organic counterparts, not the least of which are increased strength and resistance to rot. The variety of synthetic lines available also allows boaters to better match line characteristics with function.
Ironically, natural fiber rope, once the mainstay of thrifty sailors everywhere, is now often more expensive than manmade fiber rope because there’s simply not as much of it made these days. Basic construction for synthetic and organic ropes begins with fibers, which are twisted into yarns, then twisted or plied into strands, and finally twisted or braided into rope. It’s that last step that determines how the fibers lay or align with the finished line and thus defines the properties of the line itself.
For example, in a twisted or laid rope such as three-strand (the traditional form of manufacture since the early days of natural rope) fibers are not aligned with the line’s axis. This means the line will have more stretch than braided or parallel core, since the fibers straighten out as the rope comes under tension. An easy way to picture this is to imagine how the coils of a Slinky straighten or stretch out when pulled — exactly what a twisted rope does (although hopefully not as much).
Braided rope, on the other hand, has more fiber in the line’s cross section, translating to less stretch and consequently greater strength. Braided rope is torque-free, has good abrasion resistance and is less susceptible to kinking than traditional laid rope. Plaited or single-braid rope is the simplest and most prevalent type of braided rope; however, other common types include balanced double-braided (a braided cover over a braided core of the same material), core-loaded double-braid (braided cover over a braided, lower-stretch core of different material) and parallel core (a braided cover surrounding a bundled core oriented parallel to the line’s axis).
Getting Your Fiber
While exotic manmade rope-making material seemingly crops up daily, the three standbys remain nylon, polyester and polypropylene. Nylon is the strongest, followed closely by polyester and finally polypropylene. Nylon’s strength, abrasion resistance and elasticity make it an ideal choice for applications involving shock loads, such as anchor and docklines. This same characteristic however, makes it unsuitable for halyards and other uses where minimal stretch is desired.
Polyester combines the desirable characteristics of strength and minimal stretch, making it a good all-around line suited for most purposes on board. It also has good abrasion resistance, doesn’t shrink when wet and maintains flexibility in high temperatures. Purchased pre-stretched, it’s ideally suited for halyards, sheets and control lines on sailboats.
The lightest and lowest strength of the three is polypropylene. It’s inexpensive and it floats, making it the rope of choice for dinghy painters, ski tow ropes, mooring pennants and other applications where a submerged line might snag in the propeller. Downsides include less strength than nylon or polyester and susceptibility to UV degradation. It also tends to melt under high friction.
Beyond the Basics
After the three basic types, choices grow more complex — and expensive. Times were a lot simpler when all boaters had to remember was to use nylon for anchor and docklines and polyester for halyards. Now buzzwords such as high-modulus, ultra- and high-molecular-weight polyethylene (HMWPE), aramid, and liquid crystal polymer (LCP) define the cutting edge of rope technology.
The overall benefit of high-modulus — a fancy way of saying low-stretch — lines is that it takes a much smaller line to achieve the same strength, saving weight not only on line but in the gear needed to control them, such as smaller blocks and winches. A good example of just how much weight savings we’re talking here would be Spectra, which pound for pound is 10 times stronger than steel and three times stronger than polyester of equal weight, and has a strength-to-size ratio matching wire rope, yet a three-and-a-half-inch hawser of Spectra is so light it floats in water!
HMWPE lines get their strength using the same principle as the lowly plastic shopping bag: molecular alignment. During the manufacturing process, molecules align themselves in the same direction as the load, making them much stronger than random orientation, which is why those bag handles seem to stretch forever without breaking. In the case of HMWPE lines (Dyneema, Spectra, Novabraid and others), that initial stretching is done during manufacture, meaning it doesn’t stretch when first placed under load by the customer.
HMWPE is a strong, lightweight, low-stretch material good for running rigging, as well as running backstays and other applications where light weight and low stretch are critical. It also resists weather and abrasion, doesn’t soak up water and doesn’t shrink. The downside is that it’s very slippery, and the core is subject to creeping under sustained loading, meaning it will slowly stretch without returning to its original length.
Aramids are actually a family of nylons used to make anything from bulletproof vests to puncture-resistant tires. Popular brand names include Kevlar (DuPont’s trade name for aramid), Twaron and Technora. In addition to their high strength, aramid fibers possess minimal stretch and low creep characteristics. Downsides include poor UV resistance and susceptibility to abrasion, particularly when they’re subjected to high bending loads as in blocks or cleats, making them best for applications such as standing rigging.
Liquid crystal polymers are thermoplastic fibers with exceptional strength and rigidity (pound for pound five times that of steel) and roughly 15 times the fatigue resistance of aramid. A common trade name for LCP line is Vectran, which is currently the only commercially available melt spun LCP fiber available.
LCP lines have exceptionally low stretch characteristics and no creep. Water absorption is low and resistance to abrasion and flex fatigue (failure due to repeated sharp bending) is excellent; however, the lines have low UV resistance. They’re best suited for uses such as running rigging that can be covered or removed and stored away from sunlight.
Though nylon, polyester and polypropylene still serve the average boater well, there are places where these newer lines can come in handy, even for cruising boats. For instance, any situation where you want lines to resist stretching — reef lines are a good example — is a good place for something like Amsteel. It’s up to you to decide whether the benefits gained make the cost worth it, because one characteristic all of the newer, high-tech lines share is cost.
High-tech lines have quirks just like their low-tech brethren, and some of these peculiarities cause them to perform radically different under otherwise familiar situations. Knots are a good example. Knots that have served sailors well for centuries can severely damage high-modulus line to the point of early failure. Knots weaken all ropes because they distort the fibers; a bowline, for example, reduces the strength of polyester or nylon line by as much as 40 percent. That same bowline can cut a high-modulus line’s strength by 70 percent or more, leaving little or no safety margin. This means that all termination points in high-modulus lines should either be splices or end fittings instead of knots.
Tow the Lines
The final word on any good investment is maintenance and care.
Chafe remains by far the worst enemy of any rope. Visually inspect the masthead, blocks, guides, chocks, cleats, windlasses, etc., for burrs or sharp edges. Tape all cotter pins and split rings in turnbuckles and blocks (using rigging tape for this job, nothing else).
Frequently wash lines with fresh water to remove dirt and salt, which can cause excessive wear and premature failure. Soak lines in warm water with a mild detergent (some boaters recommend soap powder instead), and while you’re at it, live it up a little by adding a dash of fabric softener to make them nice and soft.
Rinse them thoroughly and then hang them up to dry. If you do this at the end of the season, the lines will be clean and ready to go in spring.
Although synthetic fibers have pretty good chemical resistance, exposure to harsh chemicals such as acids and alkalis should be avoided whenever possible. The same is true of sunlight, as UV degrades all fibers over time. Cover or remove lines and bag or store them belowdecks where possible.
Always begin coiling a line at the end that’s made fast, which allows any twists or kinks to be removed at the loose end. Most laid ropes are right-handed, so coils should be counter clockwise to ensure that lines play out smoothly. Placing a kinked line under load weakens and damages it, often resulting in hard spots caused by excessive friction heat that can literally fuse filaments together.