Cordage Basics

SailNet · #1 (**permalink**) 08-23-2000

Fiber selection is essential in choosing the correct cordage for an application. In most instances, running rigging requires high strength and low stretch. Anchor rodes require high strength and stretch to absorb shock loading, while dock lines require high strength and abrasion resistance. By combining the appropriate fibers with construction procedures, the desired rope traits and utilization are achieved.

Generally, braided ropes are lower in stretch, have a softer feel than twisted (laid) ropes and produce less friction.

Once a cordage manufacturer is selected, use that manufacturer’s size and strength guidelines.

MATERIAL (FIBER) CHARACTERISTICS

Polyester is a high strength, low stretch fiber, and when pre-stretched, provides even higher strength and lower stretch characteristics. This fiber, often referred to by the trade name Dacron, provides good abrasion resistance, maintains flexibility in high temperatures, and doesn’t shrink when wet. Use for running rigging requiring low to moderate stretch, such as mainsheets, topping lifts, travelers, and boom vangs. Spun polyester covers are fuzzy, and filament polyester covers are smooth.
Nylon has excellent abrasion resistance, high stretch, and high strength. When exposed to sunlight there is minimal strength loss, although it shrinks when wet. Its best use is in applications where stretch and shock absorption are important, as in dock and anchor lines.
Polypropylene is lightweight, has less strength than nylon and polyester, but about the same stretch as polyester. Other characteristics include low UV resistance, moderate weather and abrasion resistance, and it melts under high friction. It floats, doesn’t absorb water, and high temperatures don’t affect its flexibility. This material is ideal for towing dinghies and for rescue lines.
High Modulus Polyethylene (HMPE) is lightweight, has very low stretch, and is very strong, obtaining its strength from molecular alignment in the direction of the load during the initial stretching process. This material has excellent weather and abrasion resistance, its flexibility is not decreased by temperature, water absorption is minimal, and it doesn’t shrink. This fiber is slippery and it "creeps," getting longer under sustained loading. The core may slip when highly loaded, not making it suitable for main halyard use where halyard stability is important. It’s good for running rigging, such as halyards, sheets, guys, running backstays and checkstays, where light weight and low stretch are important. In winch and stopper use, the cover may fail before the core. Trademarked HMPE’s are Dyneema Ò and Spectra Ò.
Aramid fibers are very strong, and have low stretch with excellent creep characteristics under normal loads. They have poor UV and abrasion resistance and are fatigued if flexed over small radii (i.e. blocks) and when knotted. Twaron Ò, Kevlar Ò, and Technora Ò are trademarked Aramid fibers.
Liquid Crystal Polymers have very high strength and extremely low stretch characteristics with no creep, low water absorption, resistance to flex fatigue, and excellent resistance to abrasion. UV resistance is low. These fibers are good for running rigging that can be covered or removed from UV exposure. Vectran Ò is a trademarked Liquid Crystal Polymer.

CONSTRUCTION TYPES & PROPERTIES

Solid Braid is formed by braiding strands into a circular pattern creating a uniformly round braid of compact, one-piece construction and when cut or broken, unravels minimally. Solid braid works well with blocks.
Hollow (Maypole) Braid also known as single braid, is braided "maypole" fashion into a hollow, tubular structure producing a braid pattern without a core. Easily spliced, easy to handle, runs freely, doesn’t kink and excellent is for mainsheets, furling lines, and dock lines. Sometimes referred to as "plait" or "plaited."

Single Braid

Plait is formed by weaving, "maypole" fashion, four pairs of strands, two pair clockwise and two pair counterclockwise.
Double Braid usually has a braided core and braided cover producing an easy to handle, durable, and strong rope with good shock absorbency and water resistance. Some double braids will have a parallel core. Used primarily for running rigging and dock lines.

Double Braid

Diamond Braid has a tight, locking interlacing of yarn, which allows a core for additional strength.
Twisted (Laid) rope is usually three-strand construction, easily spliced and available in most fiber types. This is a good all-purpose rope that is durable, flexible, and easy to handle. Used primarily for anchor rodes, dock, mooring, and tow lines.

Three Strand Twisted

View Anchor Lines/Dock Lines
View Running Rigging