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HOW IT'S MADE – Membrane sails

Discover how sails reinforced with fibres placed in the directions where the greatest forces are applied are made. Three different types of membrane sails are highlighted in this news: the D4, the DFi, and the DF panel.

HOW IT'S MADE - Membrane sails (CNB Rendez-vous 2016 - Bonifacio - Photo Nicolas Claris)

Membrane sails (CNB Rendez-vous 2016 – Bonifacio – Photo Nicolas Claris)

Since the acquisition and integration of Incidence Technologies in 2013, Incidence Sails has had an impressive and integrated design office, producing its own membranes. Thanks to the company’s analysis, testing and production capacity, Incidence sailmakers now fully master the sail design and manufacturing process, from R&D to the finishing touches.

Incidence is the only French sailmaker to produce its own membranes in-house – 100% home made by experts.

What is a sail membrane?
Membrane sails have existed for a quarter of a century. Today, most sailmakers are working with this material. There are two main types of membranes: classic ones, such as the D4 membranes, that are translucent and aesthetic due to their visible constituent fibres, and filamentary DFi membranes, which appeared more recently and are generally black or grey, sometimes white.
The membranes are characterized by the structural qualities of their constituent fibres, especially in terms of shape holding, and a tailor-made design following a fibre plan that takes into account the stresses supported by the sail.

Une voile en membrane qu’est-ce que c’est ?

Video of Une voile en membrane qu'est-ce que c'est ?

Classic membranes use a composite material made of fibres sandwiched between two films. The entire part is then hot pressed at high temperature.

Filamentary DFi membranes are made of pre-impregnated composite strips deposited along very precise non-parallel trajectories to take into account the main and secondary forces applied to the sail. This material has a better shape holding than a conventional membrane. It is also lighter and cannot be delaminated.

How it’s made?
Discover hereunder the detailled manufacturing process of D4 membrane, DF pannel and DFi membrane.

D4 membrane
The D4 membrane is designed to meet performance, shape holding and lightness requirements. Whether for one-design, super yachts or maxi yachts, the D4 meets the expectations of all sailors, but ocean sailors also prefer the reliability and the look of this membrane. The D4 technology was acquired by Incidence in 2013 and has been developed by Incidence Technologies for nearly two years.

Sails are never subjected to consistent stresses. The D4 principle was developed on this basis, placing fibres where the greatest forces are applied to the sail. The draftsman determines the placement of the fibres depending on the forces that will be applied on the sail during navigation. He chooses the most suitable components and fibres for the membrane (carbon, aramid, Dyneema, or Vectran) according to the type of sail required, combining them with films or taffetas of varying thickness depending on the sailing specifications.

A close-up of D4 membrane

A close-up of D4 membrane

The films are placed on the floor to apply the fibres, and are covered with an adhesive film. A machine with a placement head holding up to 18 fibres places the pre-glued fibres, which are then dried. Next, a second film is placed on top to complete a sandwich, which is then vacuum sealed, heated and subjected to several tons of pressure. This laminating process creates a durable membrane. Finally, the sail goes through a ten-day drying process, thus acquiring its dimensional stability.

DFi membrane
The development of the DFi membrane is the first major innovation of the Incidence Technologies team. Part of the design office continues to explore every possible way to further optimise the DFi and adapt it to all offshore racing boats, as well as long-distance cruising yachts. The other members of the design office are conducting background research work based on aerodynamics and finite element modelling software, with wind tunnel testing. These studies and analyses complement each other and enable them to improve and develop the sails of the future.

Matthias de Christen, new CEO of Incidence Group

Matthias de Christen, CEO of Incidence Group, said:

“Incidence Sails has successfully combined tailor-made craftsmanship with the increasing demand from the nautical industry, as well as the skills of sail makers with the most innovative technologies. Ocean racing is rooted in the group’s DNA and the ambitious choice of investments in the DFi® filamentary membrane opens up new perspectives every day. Leader in France, Incidence Sails is a jewel that is just waiting to grow across borders”.


This filamentary membrane is made of pre-impregnated composite strips laid out along very precise non-parallel lines to carry the primary and secondary loads exerted on the sail during sailing. The pre-impregnated strips are laid and laminated on a flat table. They are placed under vacuum and then hot pressed (under more than 6 bars of pressure) before being joined together using a recyclable, solvent-free thermoplastic resin.

The membrane is manufactured in a single step. It is then shaped on the floors of the Incidence sail lofts.

Membrane DFi®

A close-up of DFi membrane

DF panel membrane
The DF panel membrane uses the same manufacturing process as the DFi membrane but, instead of orienting the made-to-measure tapes according to the type of sail, it is produced in the form of panels and the inclinations of the pre-impregnated composite strips are the same over the entire surface of the panels. This results in a material that benefits from excellent shape holding, lightweight and durability characteristics and is easy to manufacture.

> In the DF-Radial version, the panels consist of symmetrically-arranged composite tapes. These panels are then cut into widths to produce downwind sails. This lightweight yet robust material with excellent shape holding capacity is easy to work with and makes it possible to define the volumes of the sail precisely.


DF Radial

DF-Radial panel

> In the DF Cross-cut version, the panels consist of asymmetrically-arranged composite tapes. Some tapes are oriented to best withstand the sheet loads, others for the tack loads. Directions with the least loads have less layers in order to optimise the sail’s weight. This offers two benefits: stronger resistance along the sail’s load paths (close tape angles on the high stress areas such as the luff and the leech, wider tape angles on the low stress areas such as the middle of the sail), and an optimised layout to reduce the sail’s overall weight.

DF Cross-cut

DF-Cross-cut panel

Experts in their field
When two sailors meet, they talk racing. One of the secrets of the high-quality consulting work and other services provided by Incidence’s teams is that they are specialists. Whether it is the world of super yachts, classic yachts, offshore racing or offshore cruising, they are experts in their field and can provide relevant solutions.

Matthias de Christen, new CEO of Incidence Group

Matthias de Christen, CEO of Incidence Group, said:

“The Incidence Team is able to meet the challenges we are currently facing. Whether it’s supporting our customers’ projects, designing the most efficient sails, making them with attention to detail and quality, advancing the technologies of our membranes by improving their reliability and reducing their environmental impact, talents are expressed everywhere on a daily basis. They are amazing!”

Recently, Matthias de Christen has responded happily with new methods and with the support of all the Incidence Team and the shareholders of the group to new challenges, namely: the relocation of the sail-loft in La Rochelle, investments and developments at Incidence Technologie and the opening of the new sail-loft in Lorient !

Membrane sails (CNB Rendez-vous 2016 - Bonifacio - Photo Nicolas Claris)

Membrane sails (CNB Rendez-vous 2016 – Bonifacio – Photo Nicolas Claris)

Companies: Incidence Sails

Countries: France

Industries: Marine Transportation and Shipbuilding

Terms: Applications, Innovations

This article has been edited by Basalt.Today
This article has been written on JEC Composites Magazine
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