DRAFT ISAF GUIDE TO SAIL MATERIALS

Transcription

1 DRAFT ISAF GUIDE TO SAIL MATERIALS This paper is aimed at giving guidance on sail materials and construction methods for those classes which wish to place controls on these issues. Background...1 Construction of a Sail...1 Exclusion of Sail Materials from a Class...2 Recommendation:...3 Appendix A - Fibres that can be found in Sail materials...5 Background Construction of a Sail The Equipment Rules of Sailing ( ) define some basic principles regarding the construction of a sail. These are: G.1.3 Ply : A sheet of sail material G.1.4 Soft Sail : A sail where the body of the sail is capable of being folded flat in any direction without damaging any ply other than by creasing. G.1.5 Woven Ply : A ply which, when torn, can be separated in to fibres without leaving evidence of a film. G.1.6 Laminated Ply : A ply made up of more than one layer. G.1.7 Single-ply Sail : A sail, except at seams, where all parts of the body of the sail consist of only one ply. The majority of classes then go on to specify in their class rules, the material of the ply and, in some cases, control the method of the construction of the sail. Many classes used the IYRU Sail Measurement Instructions, (last published in 1986), as a guide to definitions concerning sails. In particular, it contained a default prescription which prohibited sail material that shows evidence of a DRAFT Page 1 of 14

2 film when torn. Accordingly classes which specified, Sails shall be made and measured in accordance with the IYRU Sail Measurement Instructions, prohibit Mylar sails. The Sail Measurement Instructions have been superseded by the Equipment Rules of Sailing (ERS) and the Standard Class Rules (SCR) and no longer contain this default and accordingly any restrictions on permitted sail material need to be specified in the class rules. Further sail definitions can be found in the ERS and in Appendix B of this document. Exclusion of Sail Materials from a Class Class Rules are a means for Class Associations to limit development, control costs and therefore ensure fair and safe sailing. Where sail materials are concerned, class rules may restrict the permitted materials to be used whilst racing. As many existing class rules were written before the introduction of modern sail materials, they do not extend to the full market of materials that they are intended to cover. Below are examples of rules used to restrict wording and how some sail materials aren t covered. Polyester refers to the following materials only: Polyethylene Terephthalate (PET), Polyethylene Napthalate (PEN) and all of the associated Trade Names including Dacron, Terelene, Teteron, Trevira, Diolene and Pentex. Examples of some classes that refer to Polyester as the only permitted sail material are the Optimist and J-24. The essence of these class rules is to allow woven materials only and to exclude expensive high performance materials. However, Class Associations should note that Pentex is classed as a polyester which is a high performance material that falls under the basic polyester definition. Aromatic polyamide refers to the following materials only: DRAFT Page 2 of 14

3 Poly p-phenylene terephthalamide and all of the following associated Trade names including Kevlar. An example of a class that refers to Aromatic Polyamides is the Soling. Here the essence is to restrict the use of aramids in the class. The wording used is probably too definitive and does not include other aramids such as Twaron and Technora which are referred to as aromatic copolyamides. Polyamide refers to the following materials only: Nylon, Poly p-phenylene terphthalamide, and all of the following associated Trade names including Kevlar, Twaron and Technora. Examples of some classes that refer to Polyamides are the Soling and the 470 Class, and is used in reference to the spinnaker only. The wording used is too vague with many other modern materials falling into this category such as Kevlar, Twaron and Technora. It was presumably originally intended only to allow for Nylon to be used in spinnakers as well as polyester. Polyethylene Terephthalate or PET refers to the following materials only: Polyethylene terephthalate (PET) and all of the following associated Trade names including Dacron, Terelene, Teteron, Trevira and Diolene. An example of a class that refers to PET is the J-80 Class. This is very specific wording and refers to single type of sail material. Some classes have tried to ban certain sail material types but have used incorrect wording and loopholes have appeared in the rules. Some sail materials are not considered in any of the above wording, including PBO, Spectra, Dyneema, Vectran, Carbon Fibre and Cuben Fibre. Recommendations: Classes are recommended to use the terms as defined in the Equipment Rules of Sailing, which minimises the chance of mis-interpretation. Below is a list of recommended wording and the sail materials they will allow. DRAFT Page 3 of 14

4 Polyethylene Terephthalate refers to the following materials: Polyethylene Terephthalate (PET), and the associated trade names including Dacron, Melinar, Melinex, Terelene, Teteron, Trevira and Diolene. Polyester refers to the following materials: Polyethylene Terephthalate (PET), Polyethylene Napathalate (PEN) and the associated trade names including Dacron, Melinar, Melinex, Terelene, Teteron, Trevira, Diolene and PENTEX. Aramids refers to the following materials: Poly p-phenylene terephthalamide and all of the associated trade names including Kevlar, Twaron and Technora. High Performance Polyethylene (HPPE) refers to the following materials: Spectra and Dyneema and all associated types and trade names. Liquid Crystal Polymer refers to the following materials: PBO and Vectran and all associated types and trade names. Carbon Fibre refers to the following materials: Carbon Fibre and all associated types and trade names. Cuben Fibre refers to the following materials only: Cuben Fibre and all associated types and trade names. As there are so many different variations on the chemical structure of a fibre and so many different trade names it is very difficult to include all associated fibres without writing out a complete list. DRAFT Page 4 of 14

5 Appendix A - Fibres that can be found in Sail materials Below is a list of some of the different fibres that may be found in modern sail materials. However, it should be noted that in the majority of cases the fibre name is only a trade name and does not represent the actual properties of the fibre. There are several chemical groups into which these fibres can be split. They are; POLYESTERS, NYLONS, POLYETHYLENES and ARAMIDS. Where a description is given in italic it is a direct quote from the Federal Trade Commission list of Rules and Regulations under the Textile Fibre Products Identification Act. Below is a diagram illustrating the different chemicals and the families they are derived from. DRAFT Page 5 of 14

6 Polyester: A manufactured fibre in which the fibre-forming substance is any long-chain synthetic polymer composed of at least 85% by weight of an ester of a substituted aromatic carboxylic acid, including but not restricted to substituted terephthalate units, and para substituted hydroxyl-benzoate units. Polyester is the most common fibre used for woven sail material. Its properties include good UV and flex resistance, as well as being relatively inexpensive. Traditionally white in colour although it can easily dyed to suit the sailmaker s demands. A proven fibre for durability, polyester has over recent years been replaced by higher modulus fibres, such as modern aramids, for most racing applications (where class rules permit). Woven Dacron, Polyester laminates and Polyester spinnaker cloth are all products made from this versatile fibre. Polyester fibres are also called by other manufacturers brand names of Dacron, Terelene, Teteron, Trevira and Diolene. The standard woven polyester weave can come in two forms. The first is balanced plain weave sail material, where the warp and the fill have the same amount of crimp. This induces a tight weave which is stretchy along both the warp and the fill but not so along the bias which is held by the interlock between the fibres. The second is a highly orientated weave where the crimp is limited to the warp fibres. This produces a cloth which is stretchy along the warp and the bias but not along the fill. Dacron : (Polyethylene terephthalate) or PET. Dacron is the original polyester fibre and was first introduced in 1953 by Dupont. This fibre is the foundation of traditional woven sail material. Dacron fibres are also used in cruising laminates and Polyester laminated sailcloth where the use of DRAFT Page 6 of 14

7 expensive, low stretch, aramid fibres is not necessary. The chemical structure for PET is shown below: This can be further broken down into its chemical groups by closer analysis of the structure. The ester group is represented by the chemical structure of This is the backbone of all polyesters and is present in the chemical make up of both PET and PEN. The ethylene group is represented by the chemical structure of This is the linkage part of the structure which is also represented in the structures of both PET and PEN. The ester groups in the polyester chain are polar with the oxygen atom having a negative charge and the carbon atom having a positive charge. The positive and negative charges of the different ester groups are attracted to each other. This allows the ester groups of nearby chains to line up with another in a crystalline order which forms a stronger fibre. The ethylene group used in both reactions is called ethylene glycol. This is mixed with different acids, depending on what fibre you are trying to make, and heated to burn off any unwanted residue such as methanol and ethylene glycol, which are both by-products of the reaction. Pentex : (polyethylene napthalate) or PEN. PEN has twice the stretch resistance of regular Dacron polyester (PET). Pentex also offers a higher modulus alternative to that of woven Dacron s. It is best when used in a laminate form as weaving of PEN is too expensive compared to PET. Although its modulus and stretch resistance are higher than PET, it has the DRAFT Page 7 of 14

8 same tenacity to PET and is more affected by UV degradation. This fibre is developing an impressive track record as a laminate, and is commonly found in the sails of most small offshore keelboats. The chemical structure for PEN is shown below: It is very easy to see the differences between the PET and PEN chemical structures. Where PET has only one amide ring, the PEN has a double ring structure, increasing the linear strength of the fibre. Nylon: A manufactured fibre in which the fibre-forming substance is a longchain synthetic polyamide in which less then 85% of the amide linkages are attached directly to two aromatic rings. A man-made fibre used to make the traditional woven spinnaker fabric; this material is very lightweight, but not very stretch resistant. Nylon is a generic name for any long chain polyamide and very similar to Aramids. Where para-aramids such as Kevlar are ring compounds based on the structure of benzene, nylon is based on linear compounds. Due to the wide product base of nylon, there are many different variants of the base chemical. The most common type of nylon that is used in sailcloth is the type 6,6 nylon, where the first 6 indicates the number of carbon atoms in the diamide, and the second 6 indicates the number of carbon atoms in the acid. Nylon is manufactured in varying weights ranging from 0.4oz to 2.2oz (see section on ply weights). The cloth is also sometimes coated to increase performance, such as a silicon coating to reduce friction and the cloth holding water. Nylon is also more susceptible to UV and chemical degradation than polyester. As nylons uses become more varied then extra fibres are introduced into the cloth. Available from one supplier is a nylon cloth with interwoven vectran strands for a very strong storm cloth with DRAFT Page 8 of 14

9 low stretch along both the warp and the fill. Below is the basic chemical structure of Nylon 6,6. Aramids: A manufactured fibre in which the fibre-forming substance is a longchain synthetic polyamide in which at least 85% of the amide linkages are attached directly to two aromatic rings. Kevlar : (Polyphenylene terephthalamide) or PPTA/PPD-T. This is termed as a aromatic polyamide. A gold coloured aramid made by DuPont, Kevlar's modulus is five times greater than that of polyester. Of all the high modulus fibres, Kevlar has the most proven track record, mainly due to it being the most common fibre used in racing applications. It is available in both standard K-29, and high modulus K-49 fibres, with the latter being used increasingly for applications such as boat building and high performance sail manufacture. Recently other types of Kevlar such as Type 149 have been introduced. These recent introductions are primarily due to a refinement of the liquid crystalline spinning process used to manufacture Kevlar. Despite its high modulus, Kevlar is not very durable in terms of fatigue and UV resistance. It is also more expensive. Kevlar is UV sensitive and it's gold colour turns brown as it is affected by sunlight. Another factor of its low UV resistance is a liability to stretch under load. This is seen in the used sails where the fibre has had its modulus reduced to half of its original form over a period of 3 months. Kevlar is more commonly being used as a hybrid material where it is mixed with fibres such as PBO or Carbon. Technora : This is an aromatic copolyamide and although an Aramid, is a different type of fibre to PPTA due to its chemical structure and process of manufacture. Made by the Japanese company Teijin, Technora is a high modulus fibre developed as a reinforcement for drive belt applications. In sail material, it is dyed black to help its UV resistance but is also available in its original colour of gold. Technora s properties are very similar to that of Kevlar, DRAFT Page 9 of 14

10 although it has slightly better abrasion resistance, it is more expensive than Kevlar. Technora s flex resistance is almost 20% better than other paraaramids such as Kevlar and Twaron. Although once used as the primary fibre in a sail material, Technora is now seen more as bias support for higher modulus composite laminates. Twaron : Twaron is in the same group as Technora, where its classification is of an aromatic copolyamide. High Modulus Twaron or HMT is a fibre very similar to Kevlar and Technora in its properties of modulus and tenacity. The main difference in HMT is that its UV resistance is much higher than that of Kevlar and Technora. Originally made by Asko Nobel, the rights to HMT have recently been sold to Teijin, the maker of Technora. Like all other paraaramids, it is bright gold in colour, although due to its higher UV resistance it doesn t fade. Twaron is also used in the boat-building sector where its high absorption of energy and high modulus is a benefit to creating stiff racing hulls. PBO Zylon : Poly (p-phenylene-2,6-benzobisoxazole)(pbo) is a rigid-rod isotropic crystal polymer. PBO fibre is a relatively new high performance fibre developed by TOYOBO Co. PBO fibre has superior tensile strength and modulus to Aramid fibres (such as Kevlar, Technora and Twaron). It also has outstanding high flame resistance and thermal stability. PBO fibre, furthermore, shows excellent performance, in such properties as creep, chemical resistance, cut/abrasion resistance, and high temperature abrasion resistance, which far exceed para-aramid fibres. PBO is commonly used in high performance grand prix racing laminate sail material. Although a very expensive fibre, PBO creates a high performance sail material with few disadvantages. However, it does have one major drawback. This concerns the fibres inability to resist almost all spectrums of light. Where some fibres are sensitive to UV light, PBO is sensitive to a much wider spectrum. The solution to this was to cover the fibre in an orange film which was found to be the most protective towards the fibre. (See films) DRAFT Page 10 of 14

11 Polyethylene: Polyethylene is simply formed by the polymerization of ethylene. This is done using a catalyst to initiate the process and an accelerator to allow the reaction to take place at room temperature. There are two different types of polyethylene, LDPE and HDPE. These represent LOW Density Polyethylene and HIGH Density Polyethylene respectively. It is HDPE that is more often used in the manufacture of sail material. HDPE has a linear molecular structure where LDPE has a branched molecular structure. The linear structure is important as it makes the fibre very strong along its length where the branched structure is not as strong. The chemical structure for ethylene is shown below: All of the fibres below are made out of HDPE which can sometimes be known as UHMW (Ultra High Modulus Weight). Spectra : A high modulus weight polyethylene or long chain polymer, Spectra is a product of the Allied-Signal Corporation, now known as Honeywell. Spectra has a higher modulus than most fibres, except for carbon and PBO. First used in sail materials around 1987, it was originally used instead of Kevlar but its low stretch resistance meant that it was soon discarded from racing applications. This stretch makes it difficult for the sail designer to guarantee the shapes they want after manufacture. As a result, Spectra is viewed more as a performance cruising fibre where its excellent flex, UV and chafe properties along with its traditional white colour are perfect for large cruising boats where cloth strength and durability as well as weight are considerations. Spectra is often found in laminates where it is bonded between taffeta for performance cruising sail materials. Dyneema : Produced by the Dutch company DSM, Dyneema, like Spectra is a highly processed polyethylene, which offers good UV resistance, high theoretical initial modulus and breaking strength. It also shares Spectra's DRAFT Page 11 of 14

12 creep characteristics. It has almost exactly the same properties as Spectra except that it is more commonly available and slightly cheaper to produce. The method of manufacture for both Spectra and Dyneema are very much the same. In normal polyethylene the molecules are not orientated (like a branched molecular structure), and can be easily torn apart. To make strong fibres, like Spectra and Dyneema, the molecular structure needs to be orientated and crystallised in the direction of the fibre. This is why a HMPE (High Modulus Polyethylene) is used as a starting material as this is of a linear molecular structure. This is then processed using a gel-spinning process which draws the fibres out of the melt. As the fibre is drawn through the gel solution, it is disentangled and once cooled, it forms filaments. Due to the low degree of entanglement the fibres can be super drawn which straightens the structure and produces a high level of orientation. It is this orientation that defines the initial modulus of the fibre. Vectran : A wholly aromatic polyester-based, liquid crystal polymer fibre manufactured by Hoechst Celanese. First produced for the US Navy for towing arrays from submarines. Vectran has a modulus comparable to Kevlar but due to its molecular composition has better flex and abrasion resistance, although its UV properties are worse. Vectran, unlike Spectra or Dyneema, does not creep. These characteristics make Vectran an interesting candidate as a performance fibre, although it is more expensive than either Kevlar or Spectra. Vectran is uncommon as a laminate and can normally be found as a hybrid cloth with polyester. The chemical structure for Vectran is shown below. DRAFT Page 12 of 14

13 Certran : A high modulus polyethylene fibre, similar to Spectra, manufactured by Hoechst Celanese. This fibre shares the same resistance to flex fatigue and UV as Spectra so its applications in sailcloth are limited to secondary fibres and areas which can take advantage of its flex, chafe and UV resistance. Very rarely used in modern sails as the price of Certran limits its use to a small percentage of the market. Due to its limited availability and cost, production of Certran has been stopped. Carbon Fibre: Carbon has only recently been accepted into offshore classes over the past couple of years, although the fibre has been under development for over fifty. Carbon was first used during the 2000 America s Cup with varying degrees of success. Due to the many different types of manufacturing processes there are various chemical types of carbon fibre available. Carbon is originally a very brittle, but strong fibre. Its primary application was in building applications such as boats. Here its brittleness isn t such a worry as the fibre is cured with resins to form an extremely strong hull. However, when carbon fibres were first introduced into sail materials, which are constantly being folded and creased, the brittle nature of the fibre led to many failures of the sail. A lower grade fibre is now used in sail materials, which still has an exceptionally high modulus and tenacity, but also has the lowest amount of stretch of any fibre and more importantly, has a good flex life. It is also completely resistant to UV degradation making it perfect for high end racing applications. Since Carbon has become a legal sail material in Offshore Classes, its cost has dropped to that of Kevlar as the development continues to improve the fibres properties. Carbon is being used in all methods of sail manufacture where in the 3DL and TapeDrive process it is being used alongside Kevlar in a hybrid form to create a super strong, low stretch sail. Cuben Fibre: Firstly it should be pointed out that Cuben Fibre is only a trade name and a process for manufacturing sail material. It is not a specific cloth or contains any one fibre. The Cuben Fibre Corporation claim that its fibre/film content is very similar to other laminate cloths. The fibres may vary from spectra or dyneema to aramids such as Kevlar etc. The film is a polyester film called Mylar with another similar material called Tedlar on top of everything. DRAFT Page 13 of 14

14 As Cuben Fibre can be made out of many different materials it is hard to define exactly what type of cloth it is but it is essentially a very expensive laminate. The method used to produce the cloth makes it expensive seeing that it is virtually hand made. A combination of films and fibres are laid down by hand to form the essential sandwich of the laminate. This is all then bonded under extreme pressure in an autoclave to produce a very light cloth. The autoclave itself is only 30 feet long so therefore only roll lengths of this length can be produced. This and the complex nature of the manufacturing process makes Cuben Fibre the most expensive and the most demanded sailcloth on the market. N.B It should be remembered that the chemical structures displayed in this report may be displayed in different formats. DRAFT Page 14 of 14