By Frank Lanier
Chesapeake Bay Magazine
February 2004

Whatever your boating stripes, power or sail, a common thread joins us all – rope. The quality and variety of rope available to boaters is constantly evolving and growing, so it’s more important than ever to be able to choose the right rope for a particular job.

Rope is the generic term for cordage over one 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 tack on board (a spring line for example). For our purpose, we’ll view the terms rope and line as interchangeable.

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: material, method of construction and what exactly it is you want the rope to do.

Rope Construction

The vast majority of lines found onboard today are made of synthetic fibers like 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, so 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 a ® Slinky’s coils straighten or stretch out when pulled—exactly what your 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, excellent abrasion resistance, and good elasticity make it an ideal choice for applications involving shock loads, such as anchor and dock lines. This same characteristic, however, makes it unsuitable for halyards and other uses where you want very little stretching. As for price, ½” three strand nylon rope cost around $.64 per foot (for simplicity, we’ll use ½” size rope in all our price examples).

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. Polyester lines are known to many boaters as Dacron, DuPont’s trade name for the material. Average price for ½” double braid polyester is approximately $1.25 per foot.

The lightest and lowest strength of the three is polypropylene. It’s inexpensive (around $.15 a foot) and it floats, making it the rope of choice for dingy painters, ski tow ropes, mooring pennants, and other applications where a submerged line might snag in your propeller. Downsides include less strength than nylon or polyester and susceptibility to UV degradation. It also tends to melt under high friction.

After the three basics, choices grow more complex—and expensive. Times were a lot simpler when all you had to remember was to use nylon for anchor and dock lines and polyester for halyards. Now buzzwords like High-modulus, HMWPE, Aramids, and LCP define the cutting edge.

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 in lines but in the gear like blocks and winches needed to control them. A good example of just how much weight savings we’re talking here would be Spectra® - it’s pound for pound ten times stronger than steel, three times stronger than polyester of equal weight, and has a strength-to-size ratio matching wire rope, yet a 3.5” hawser of Spectra® is so light it floats in water!

High molecular-weight polyethylene (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, that initial stretching is done during manufacture, meaning it doesn’t stretch when first placed under load by the customer.

Trade names include Spectra®, Amsteel® and Dyneema®. HMWP 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. You’ll recognize them in the names Kevlar (DuPont’s trade name for aramid), Technora and Twaron. 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. Technora line (1/2”) is around $4.50 per foot.

Liquid crystal polymers (LCP) 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 do have low UV resistance. They’re best suited for uses like running rigging that can be covered or removed and stored away from sunlight. Average price for ½” Vectram is $8.00 per foot.

While high-tech lines are most common on racing sailboats, they have many commercial applications as well. Amsteel® is a popular towing hawser with tugs not only due to its strength, but because it doesn’t store energy like nylon (meaning it won’t snap back with lethal force when parted).

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 also have quirks just like their low-tech brethren (creeping, extreme slipperiness, etc.), and some of these peculiarities cause them to perform radically different under otherwise familiar situations. Knots being 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 rope and running rigging 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 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, your 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 below decks where possible.

As for line handling, 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.

The advent of space-age fibers and lines may require a little more research to ensure that you’re buying the line best suited to meet your needs, but it doesn’t have to be rocket science. As always, selection, use and care of line involves a healthy blend of reasonable expectations and common sense – just be sure to read the operating instructions.