Tuesday, March 4

Cordage 101

Cordage 101
By Michael Argyelan

Strings, lines, ropes, running rigging, cordage, whatever you want to call it, understanding the basics of cordage is an important aspect of being a good sailor. If you don’t know the breaking strength of your halyards, you might be putting yourself and your crew at risk. Do you know what stretch and creep are? How about core dependant versus cover-core dependent? No? Well you will after reading this article. First, let’s explore the fibers and materials used in the covers and cores of lines.

Polyester: A general grade line for applications not too concerned with stretch. Most covers of lines are constructed of polyester. There are different grades available to the line manufacturer, which affect color retention, sheen, wear and UV degradation. Polyester stretches less than nylon, and is durable and economical.

Spectra: Very strong and durable. It has super low stretch, and is light enough to float. Spectra has the best fatigue life of most any fiber. One issue with Spectra is “creep”; under high static loads (think main halyard), Spectra will elongate very slowly. After a period of time, you might notice that your main halyard now seems an inch looser. Using one size larger will greatly reduce creep, but it may still be noticeable. Spectra is the ultimate material for high fatigue and lightweight spinnaker halyards, guys and sheets. Spectra does not absorb moisture, which keeps it lighter on the boat.

Dyneema: Dyneema is like a fraternal twin to Spectra. Dyneema has a slightly different molecular structure than Spectra and higher breaking strength in the larger diameters. It displays slightly better wear characteristics in heavy use areas, but has more elasticity than Spectra. Like Spectra, Dyneema has a relatively low melting point making it susceptible to friction damage.

Vectran: A liquid crystal polymer fiber, it is another fiber that is very popular for low stretch applications. This fiber has very low stretch and high breaking strength, low creep, good in tight bends, and has good chafe resistance. Vectran is very popular for control lines and halyards requiring extremely low stretch. It has an excellent track record and is used on many boats. Vectran is an alternative to Dyneema as it has less stretch and creep, although it does not have quite the fatigue life or UV resistance of Dyneema. It is also slightly heavier and does not float.

Technora: Technora is an Aramid fiber, similar to Kevlar. It has very high strength and low creep, but is more susceptible to fatigue, especially around small diameter sheaves and tight bends. It is also very susceptible to UV degradation and so must be protected with a cover or a coating on the core. It is more suitable for halyards and other lines that remain static when loaded. Cruiser/day sailors with furling jibs that stay up all year would benefit greatly using a line with a Technora core.

Creep vs. Stretch: Creep is non-recoverable elongation, whereas stretch is elasticity or recoverable elongation. A “stretchy” line (ie. Polyester) will return to approximately its original length when unloaded. Lines that are prone to creep or elongate (especially Spectra or Dyneema) will gradually stretch under load but will remain at the stretched length after the load is removed. They will eventually stretch and then creep to failure. All line materials are susceptible to stretch and creep. Now let’s explore the difference between a core dependant line and a cover-core dependant line.

This image shows a polyester cover and a Spectra core.

The typical day sailing boat with run-of-the-mill cordage is likely to have cover-core dependant lines on their boat such as New England Ropes Sta Set (polyester cover and core). If you’ve ever looked at your lines closely, you’ll notice that there’s a cover (white or colored with some sort of flecked color or a solid color without a fleck) and inside is either a white or colored core. The strength of a cover-core line is completely dependant on both the cover and the core being in optimal condition.

Let’s say you have a main halyard that is starting to chafe in the area near the shackle where the line goes around the sheave when at full hoist. Any chafe on the cover of your halyard essentially means that you now own a compromised line holding up your main sail. The strength of the halyard is dependant on the cover and the core working together.

Lines can also be compromised by UV degradation. Have an old halyard that is left on the boat year round with the mast up? It’s likely that your cover-core dependant line has UV degradation and its strength has been compromised. Nothing like a halyard snapping during an enjoyable day sail to ruin that freshly poured rum drink!

Core dependant line is just that, the strength characteristics are dependant on the core of the line. Many, if not most, common core dependant lines have polyester covers to help protect against UV degradation, provide better chafe resistance, and make the line easier to handle. However, the difference between a cover-core dependant line and a core dependant line is, if the cover starts to chafe or break down due to high UV degradation, your core is likely still operating at a high level and uncompromised like a cover-core dependant line.  

Typical core materials are likely to be the ones we covered earlier in this article: Spectra/Dyneema, Technora/Aramid, and Vectran. Many race boats will help save weight on the boat by stripping back the cover of the line except where the line meets the clutch or winch and leave just the core of the line exposed. Doing this of course limits the life of the line as the core is now exposed to UV and chafe but has not changed the strength of the line.

This image is of a Spectra core.

Some lines are sold without a cover at all. Of these, some have a special coating to help with UV issues, and others do not. In fact, many boats have started to use Spectra/Dyneema lines in lieu of wire for lifelines as the cordage is lighter and in most cases, stronger than the wire they replaced.

This image is of Yale PhD cordage. This is the example of where a “cover” is simply spun over the Spectra “core”.

Not all lines have a “core” per se. Some lines like Maffioli Swiftcord and Yale PhD have the “cover” spun around the “core” and therefore, look like a core only line. Most often the spun cover is there to protect the core of the line from chafe, UV, and to provide a good “hand” or grip when using the line. The polyester (likely) spun cover also provides a good grip on winches, cam cleats, and the like. Some spun materials will even have an added “special sauce” to it so grip is enhanced. Yale PhD uses what they call iGrip to improve the feel and grip. A huge bonus of lines like these is that they are very light, feel great in the hand, and have almost unbeatable strength to weight ratios.

Of course there are also other lines made from other materials. Some lines are made of mixed materials like poly/aramid covers, etc. In the world of running rigging materials, it’s sort of like Burger King, have it your way.

Choosing line diameter: To determine what line size (diameter) is appropriate, you will need to know what size line your winches (self tailing), clutches, blocks, and sheaves can handle. You may want a big, fat, grippy 1/2" line for your jib sheets, but if your self tailing winch can only handle up to 7/16” line, then the max line you can use is 7/16”.

The same criterion applies to halyards. If you want a larger diameter line because it’s easier for your crew to hoist and easier on the hands, you will need to know if the halyard sheave at the top of the mast can handle the line size you want. You will also need to know the max diameter that your clutch and cabin top self tailing winch can handle. If you have a mast base block and deck organizer (likely) then you will have a max diameter that you can use in those too.

Someone with little to no knowledge of cordage would think choosing line is pretty easy. Pick a color, pick the size that feels good, and go. This is obviously not the case. Or at least it’s hopefully clear to you after reading this article! Always pick your running rigging based on the application, the performance and characteristics of the line, the size of your sheaves, winches, clutches, and then and only then, your budget and favorite color.

A quick note on splicing: We highly recommend that you splice halyards to your shackle. A proper splice will retain almost 100% of a line’s given breaking strength. When you tie a bowline knot, you will lose almost 20% of the load carrying characteristics. As you may have noted above, some high tech lines don’t perform well in tight bends. This is even more reason to have your halyards spliced to a shackle.

If you have any questions on cordage, want a running rigging inspection of your vessel, or advice on the right lines for your particular boat, please do not hesitate to contact me at mma@crowleys.com or 773.364.1344. I hope this finds you well and warm.

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