Aren’t you changing the boat? Get new sails! Second installment

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Indio Bisce proa 1We have seen that thanks to fluid dynamics programs. it is possible to minimize error rates: “Until fifteen years ago, everything was done by eye,” Fabio tells me, “from choosing which ring to put on the ashlar to guessing how many kilos of stress a particular point had to bear. Today I can know for sure how many kilos of stress there are at the various points and use appropriate materials and equipment.”

 

ListenerTHE STRUCTURE IS THE MATERIALS USED
Without proper structure, the form does not exist. Aerodynamic forces generate stresses on the sails, strains that then cause deformations in the materials. Fluid dynamics studies aim to determine what materials are best to use to build a sail: “If you don’t have a structure, a proper material, the shape will not be efficient. Even in cruising, if the sail over the years deforms, it becomes less efficient, the performance will come less, the boat will drift more, etc.” It is therefore necessary to understand, if the intention is to change the sails, what materials are available and what thoughts have been given by experts in the field on the various types of structure. There are three major families of materials in the market today: polyester or Dacron, laminates, and fiber-oriented membranes.
Trioptimal vs horizontal Dacron

THE IMMORTAL DACRON
Polyester, known as dacron, is still the most widely used fabric for sailmaking. Characterized by a weave (warp and weft) constitution, it is still the cheapest material today. Technology, in recent years, has also improved for Dacron : polyester fiber has improved, as has the machinery used. But what is the secret of so much success? Certainly its durability, still unbeaten by any other material: “The secret of polyester fiber is that when subjected to heat it shrinks by 20 percent”-Fabio explains to me-“creating a very stable structure. Therein lies the uniqueness of this fiber; however, its limitation is that, having a very low modulus (fiber resistance to elongation caused by wind force), it tends to stretch.”

Triradial Laminate

ROLLED LAMINATED MATERIALS: MANY LIMITATIONS
Laminate is a composite material, usually it is two layers of film sandwiched (outer layer, fibers and glue) to various fibers such as kevlar, carbon, dyneema, technora, etc. characterized by predisposed fibers in direction and percentage. Thus, it is a multilayer material with a bottom backing of glue coated film, a spaced network of fibers on the inside, and another layer of film to close. It all goes into a machine that with heat and pressure “crushes” them together. However, the laminates have a weakness: “The fiber resists stress well in the direction in which it was placed, but is not as resistant to forces coming from different angles. Any other load that deviates from this direction results in elongation. The goal of laminates has been for fiber capacitances to follow the lines of greatest stress. Once it was determined where the greatest forces acted, materials were oriented accordingly, using warp-oriented laminates in the areas of greatest stress: pen, wall, ashlar, and terzaroli hands. “The greater the strain, the more layers I went to put in the direction I needed. Obviously these reinforcements are going to weigh down and ruin the shape of the sail a little bit.” In addition, laminates have another major limitation: delamination, due to air remaining between the glue and the materials.

EPEX film vs grey taffeta

THE NEW FRONTIER: ORIENTED FIBERS
Oriented fiber materials, more commonly known as membranes, are an evolution of laminates. They differ from the latter in that the various components are laid one after the other by means of a plotter (a rotating head) that lays out the individual fibers according to a direction given by a program that follows the sail’s major stress points. These oriented fiber materials open up new possibilities for sail structuring: by improving the direction and density of the fiber strands where needed, they allow for lighter, more efficient sails with better shape retention: the internal fibers, if they have been properly engineered, perfectly maintain the tension to which they are subjected. Starting from the limits of the laminates, the next step was to put fiber strands as and where you want on the resulting structural calculations. “Have we determined that the effort is there? I place a fiber there in the direction I need. Thanks to special programs to ‘fiber,’ that is, to place the fibers in the direction and density I need. For example, if I am making a lightweight carbon genoa, it is not necessary to fill it with carbon, I will not need a lot of fiber. These programs also allow you to simulate strain points using certain fibers rather than others, with the goal of creating the most efficient fibers possible. All the fibers start from the corners of the sails, so in these areas we will also find the highest concentration: this allows me not to have to put additional reinforcements: the more fibers you put, the greater the bonding problems will be.” The oriented-fiber structure is also an open construction because you can change the type of fibers, direction, density, but also the backings: you can have bare mylar-type film alone (racing), or film plus double taffeta (a Dacron film) that protects, or a layer of taffeta on the inside (cruising), depending on the use. Also, you never make sails all with one fiber, but you make mixes: dyneema+carbon, technora+carbon, kevlar+carbon, so that if one fiber breaks, there is the other one that holds. Each fiber will then be exploited for its own characteristics by forming a network of multiple strengths (elongation strength, breaking strength, etc.).

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