Stratis Fiber Selection
Stratis offers our designers and engineers unmatched flexibility in both fibers and fiber layout, allowing them to precisely tailor the composition of the sail to match the needs of the boat. Below is an overview of the most common fibers used in Stratis sails and their key benefits.
Technora is a gold or black colored fibre originally developed to replace steel belting in tires. It is a very durable fibre and is resistant to breakdown from either flex or UV. Technora has low stretch characteristics but does not out perform carbon or Kevlar in this field. It is particularly suitable for combining with Carbon or Twaron in a sail to increase durability.
Technora is a copolymer, which means it is comprised of two different building blocks instead of just one. The second component that is added to the structure introduces a regularly repeating kink in the polymer backbone. This lowers its modulus compared to Kevlar, but more importantly significantly increases its flex fatigue, while leaving the tensile strength largely the same. Hence it is used to reinforce in those areas where we anticipate a lower initial load, but require it to keep its strength for longer.
PEN (more commonly referred to as Pentex) is the big brother of PET. It was invented very shortly after PET but only commercialized in the 1990’s after Amoco started the first plant to produce the NDA needed to make it affordable in commercial quantities. Recently the price of PEN has been rocketing as almost all the capacity worldwide is being used for producing tires; it is now comparable in price to Kevlar.
PEN does provide a reasonably significant increase in modulus over PET, so is very useful in those classes limited by Class Rules to lower modulus fibres (or simply “polyester” fibres – though Vectran would actually pass this criteria). One cosmetic issue with PEN is that the naphthalate in the polymer is prone to yellowing on exposure to UV light. The yellowed polymer is only a few micron thick, and if you poke underneath you’ll find the virgin white polymer unharmed as the yellowed material actually acts as a sunshield. There is an associated loss in mechanical properties proportional to the amount of yellow sun-shield material, which is not really that significant, but is pretty ugly – so more expensive measures are needed to protect it from UV damage.
Polyester is naturally a white fibre but it is also available in dyed black. It is the fibre that is used in the various forms of Dacron in a woven form as well as in cruising laminates produced by sailcloth manufacturing companies. Polyester is a cost effective and relatively stretchy fibre which helps to keep the loads on sheets and attachment points down due to the elasticity in the sail.
The use of polyester in a Stratis GPc sail is particularly suitable for small to mid size cruising sails. The shape holding advantage that using polyester as a laminate gives over a panel sail construction is substantial over a wide wind range with the additional performance benefits from specifically engineered reef points. Polyester fibres provide performance and durability as a cost effective option to cruise laminates commonly used for performance cruising sails.
Vectran (Liquid Crystal Polymer) is a light brown fibre with significantly lower stretch characteristics than Polyester, but many other similar properties. The fibre copes well with flexing so it is especially suitable for performance cruising sails. Vectran however does not have good UV resistance so it should always be specified in conjunction with polyester taffetas on the outside surfaces of the sail to provide protection from UV.
Vectran is suitable for mid to large cruising sails where performance and light weight are desirable.
Kevlar and Twaron are similar aramid fibers that have become very common in the racing sector of sailcloth. It is stronger than steel for its weight and has a modulus that is five times greater than polyester. Drawbacks of these aramids include poor UV resistance (Kevlar loses strength roughly twice as quickly in sunlight as polyester and, when affected, the gold Kevlar fibers turn brown) and rapid loss of strength with flexing, folding and flogging. Minimal flogging and careful handling can greatly extend the life of these sails. Twaron and Kevlar are very good all-around fibres at the high-performance end of the spectrum, where they have good modulus and strength, but lower than average resistance flex fatigue.
Carbon fiber is a black fibre which has the highest strength and lowest stretch of all of the fibres we use. Carbon is used where light weight and low stretch are essential for sail performance. Carbon is often combined with other fibres in the laminate for added durability.
The modulus and tensile strength of carbon fibre used in Stratis membranes exceeds that of all the other fibres but comes at a price with the brittle nature of the material resulting in far lower resistance to flex fatigue. It is however virtually impervious to UV degradation, and when used appropriately it is a very useful fibre for medium to large cruising yachts and superyachts which have boom-furling mainsails that limit the bend radius of the fibres while in storage.