The advent of nylon spelled the end for the use of hemp and sisal in rope manufacture for leisure sailing. A wide range of synthetic fibres is now available for rope construction.
Polyester is the most commonly used fibre for running rigging on a yacht or a dinghy and features widely in all rope manufacturer’s ranges. High performance fibres like Dyneema® and Kevlar ® are also used but they are more expensive due to the nature of their manufacture.
The polyester yarn used in rope manufacturer is usually Medium Tenacity (MT) or High Tenacity(HT) polyester, a more expensive yarn that is particularly good at resisting wear and abrasion. Polyester melts at 250 centigrade and sinks in water. It is chemically resistant to common solvents and cleaning agents and has good resistance to UV light. Polyester typically stretches by 10% at 50% of its breaking load. Construction method , heat setting and pre-stretching can help reduce this as low as 2% at 20% of working load in some ropes.
Nylon provides a good combination of strength and stretch which is particularly useful for mooring applications. 3-strand nylon stretches by about 15% of its length when loaded to only 15% of its breaking strength so it can act as a shock absorber to prevent damage to cleats and anchoring points in bad weather or exposed locations. Nylon is usually used as the core for dynamic climbing rope because of its elastic properties.
Polypropylene is popular for dinghy sheets because it floats and does not absorb water. It has up to 15% stretch at 50% load so it is not suitable for static loads like halyards or rigging. It is however sometimes used for the outer cover of high performance ropes where the core is doing all the load bearing work. Polypropylene is susceptible to UV damage and you will notice coloured polypropylene fades over time.
HMPE (Dyneema® or Spectra®)
High modulus polyethylene is available as trademarked Dyneema® and Spectra®. It is an extremely strong and low stretch fibre. There are different grades of Dyneema® ranging from SK60 to SK90 and each has different characteristics (and prices). In general Dyneema® SK75 is used for running rigging applications although the higher performance variants are now being used on yachts in the Grand Prix and Super-yacht circuits.
Dyneema® has a specific gravity of .98 so it floats in water. With very low stretch characteristics it is ideal for halyards and winch lines. It can also be used for sheets and control lines where higher performance is needed. Whilst it is very UV stable it is often covered with a polyester or polypropylene cover for handling and durability.
Since Dyneema® melts at a relatively cool 150 centigrade aramids like Kevlar® or Technora® are often used in a cover to help protect it from overheating on winches. To put its high breaking load into perspective Dyneema® is around 15 times stronger than steel of the same diameter and because it doesn’t store energy like steel there is no “back lash” if it snaps under load making it a much safer choice than steel wire in many cases.
Kevlar® & Technora® are high strength low stretch aramids. They do not “creep” under normal loads but they are prone to fatigue if they have to go around short radius turns. Aramids do not burn and they retain their strength at very high temperatures.
A unique liquid crystal polymer Vectran® was developed over 30 years of R&D. It’s very strong and does not creep however it is prone to UV damage so it needs to be covered with another fibre to prolong it’s life.
A biopolymer that is extremely strong and has practically no stretch Zylon® is starting to replace wire for standing rigging. Although it is expensive the reduced weight and rigging costs make it a viable choice.
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