Abstract

Although modern sailcloth materials are extremely complex, a considerable degree of disorder is still present in the evaluation of their quality, and experience is still the most important parameter in assessing a product. For those reasons, precise characterization and evaluation of modern sailcloth is a topic that asks for systematic investigation, both in view of defining relevant characteristics and parameters and in defining and adapting adequate testing methods and procedures and evaluation of results. The paper presented here is a contribution to the scientific and professional approach to the topic.

Key Words:

Sailcloth, Objective evaluation, Quality characterization

1.Introduction

Objective measurements and evaluation are now an integral part of the preparation, marketing and processing of many textile goods [1], but for some of them like, sailcloth for example they are still not in use [2]. Although modern sailcloth belong to the group of high performance and high tech materials the assessment of their fitness for use is based mostly on sail-maker subjective judgement and experience [3]. In order to implement the concept of objective measurements and evaluation in the sail-making processes (Fig. 1), possibilities of objective characterisation of materials intended for sail manufacture are investigated and defined, with the respect of specific principles of sailing and requirements on the material for the purpose [4].

A material (cloth, yarn or fiber) should meet a number of requirements to be used in sail manufacture. These requirements can, depending upon a particular point of view (naval architecture engineer, sail-maker or sailor [5]) be somewhat contrary to each other, can supplement each other and/or be the same (Fig. 2).

From the naval engineer's point of view, a material to be used in sail manufacture should, besides having smooth surface, have zero porosity, ensuring effective air flow around the sail [2, 4, 6] and creating aerodynamic force to push it. To reduce the part of the force created that cannot be used, i.e. resistance to airflow, surface roughness of the sailcloth should be as low as possible. Further requirement, or limitation, to be met by the sailcloth is low surface mass, so as to reduce the moment of swerving and with it tilting of the sailboat.

The sailor, similarly to navy engineer, as the end user of the sail, asks for the sails of lower mass, to facilitate handling. However, to sail more comfortably and safely, the yachtsman also wishes strong sails, of stable shape, and easy to maintain. Sail strength (cloth and joining parts and/or seams) should be such that the sails can stand strong wind or sudden squalls and not get torn or change the shape significantly, as it reduces the need to adapt sail shape instantly to momentary conditions. In addition, resistance of the sailcloth to water, sunlight and microorganisms is required, as well as a good ratio of price and durability. Final decision in selecting the fabric for the manufacture of sails rests on the sail designer. His task is to turn the designed shape into a sail, balancing the forces of wind and strains in the sail.

As each particular sail is designed for precisely defined range of wind strength, the resulting pushing forces of the wind on the sail will determine the limits of necessary fabric strength. As push is highest when sailing downwind, breaking force will be a decisive factor in manufacturing spinnakers, while in selecting the fabric for headsail and main sail (where stability of form is more important than maximum force), decisive factor will be yielding point, or fabric elasticity [2].

2.Methodology

Having in mind the above goal, but also considering the possibility of establishing an expert system that would make possible the evaluation of material behaviour under real end-use conditions, 12 representative samples of modern sailcloth of various constructions have been selected (Tab.1).

The samples have been used to test six groups of properties (or parameter blocks), that determine in detail the suitability of a particular material for the manufacture of sails of predetermined end-use properties (Fig. 2). The parameter blocks are as follows: chemical composition, macro- and micro-construction, sorption properties, resistance to wide variety and intense of forces, and resistance to ageing under natural conditions.

Appropriate standardised testing methods (Tab.2) have been used to investigate the above properties, some of them for the first time for such a purpose (KES System). Statistic evaluation of the importance of each quality factor has been implemented to assert the suitability of selected parameter blocks.

3.Objective measurements and evaluation of sailcloth


The systematic approach to objective material characterisation (Fig. 2) has resulted in a sailcloth quality card as a kind of quality assurance, and a key element for production optimisation and improvement of end-product quality. The quality card that includes Fig. 3-6 & Tab.3-6 is designed so as to enable:

. Primary classification and sailcloth evaluation by end-use (manufacture of racing or cruising sails) as well as by the weather-location conditions of the use supposed. Although the decision can be made on the basis of a number of indicators, the most evident one is the time of cloth destruction and the trend of the change in tensile properties, as effective aerodynamic flow and optimal maritime sail properties are higher on the scale of importance than durability, at least for racing sails.

Secondary classification and sailcloth evaluation based on the end-use and defined by naval architect requirements for the type of sails adequate for the type and size of the vessel designed. For example, establishing the required size of the sails for the purpose of sail-ship stability sets limits to maximum sailcloth surface mass. It is also possible, on the basis of surface roughness and adequate friction coefficient, to define precisely the effectiveness of aerodynamic airflow, which means the efficiency of the sail itself.

. Tertiary classification and sailcloth evaluation based on sail maker's requirements for processability of a 2D fabric into a 3D sail form. For example, quality parameters (determining resistance to tensile forces) in a particular direction of the sailcloth is a key factor in designing sails and selecting the technique of its manufacture (panel or radial cut).

. End-user sailcloth evaluation, as he considers an ideal cloth to be the one with as low a ration of price and durability (raw material content; appearance; weathering resistance), which at the same time offers reaching maximum maritime properties for the sail ship (as low a ratio as possible between sail strength and its mass and as smooth a surface as possible) and security (resistance to high loads and prolonged tearing; weathering resistance), as well as easy handling and maintenance (flexing ability; compressibility; volume mass; hydrophobicity).

4.Conclusion

The investigations described and knowledge obtained, offer a basis for the construction of an expert system to be used, starting from objective measurements of each new and potentially applicable sailcloth, to evaluate the behaviour of each sailcloth material in its end-use and assess its value, usability and effectiveness for a particular end-use.

References

[1] P. Sommerville, Objective Measurements - more than pretty numbers, Proceedings of Australian Wool Testing Authority Seminar - Working with Wool, Canberra, 1998

[2] B.E. Doyle, Strong Fabrics for Fast Sails, Scientific American, 1997, 277, 7

[3] E. Vujasinovic, R. Cunko, Spectra - one of the latest sailcloth wonder fibre, Proceedings of the 1st AUTEX Conference TechniTex 2001, Ed. Mario Araujo, Povoa de Varzim, 2001

[4] E. Vujasinovic, Istrazivanja mogucnosti objektivne karakterizacije materijala za izradu jedara,
Dissertation, University of Zagreb, Croatia, 2003

[5] T. Whidden, M. Levitt, The Art and Science of Sails, St. Martin's Press, New York, 1990, 11-72

[6] W. Ross, Sail Power - The Complete Guide to Sails and Sail Handling, Alfred A. Knopf Inc., New York, 1989, 375-424

Acknowledgement

Investigations presented here are a part of broader research project organized at the Department of Textile Chemical Technology and Material Testing, Faculty of Textile Technology, University of Zagreb, Croatia, in collaboration with a well-known sail-maker company (Victory - Intervela d.o.o., SI). Here we also wish to express our gratitude to Prof. Ph.D. Jelka Gersak for giving us opportunity to perform some new, nonstandardized tests in her laboratory at the Faculty of Mechanical Engineering, University of Maribor, Slovenia, during CEEPUS exchange program.

About the author:

Ph.D. Edita Vujasinovic, Assist. Prof.
Department of materials, fibers and textile testing
Faculty of textile technology
University of Zagreb
Prilaz baruna Filipovica 30
HR-10000 Zagreb
Croatia
Phone: 385 1 37 12 567
Fax: 385 1 37 12 535
e-mail: edita.vujasinovic@ttf.hr

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