What's a membrane sail?
Membranes have been around for 25 years. Today the majority of sailmakers work with this material. But not using the same technologies because there are 2 types of membranes:
- The so-called "classic" membranes . In incidence it is called D4. They are translucent and the fibres that make it up remain visible.
- The filamentary membranes . At Incidences it is called DFi. These membranes have appeared more recently. They are usually black or grey, sometimes white.
How is a membrane made?
Membranes are characterised by the structural qualities of the fibres that make them up, particularly in terms of shape retention, and by a tailor-made design according to a "fibre plan" that takes up the stresses undergone by the sail when sailing.
Manufacture depends on the type of diaphragm :
- A classic membrane is a composite material, made of fibres sandwiched between two films. The whole is then pressed at very high temperatures. For these "classic" membranes only the fibre yarns are structurally effective. The film is only there to bind the fibres together.
- Filamentary membranes, type DFi, are made up of prepreg composite strips deposited along very precise non-parallel trajectories, in order to take up the main and secondary forces applied to the sail when sailing. The whole thing is pressure-rolled, at 7 bars, hot.
One of the particularities of DFi, Incidence's filamentary membrane, is its lightness (72 kg for an IMOCA mainsail). Made without film, everything is indeed optimized and structurally efficient at the heart of this composite material.
This material has a better shape retention than conventional membranes, it is also lighter and cannot delaminate.
Advantages and disadvantages of the different types of sails
Dacron type fabric sails are very durable over time, but the strong deformation of the fabric quickly diminishes the performance of the sail.
The D4 membrane benefits from a very low deformation, but with risks of delamination in the long term (delamination of the different layers). This is the case for all conventional membranes, their durability will depend on the quality of their design (including lamination).
DFi surpasses all the characteristics of classic membranes. His deformation is almost nil. There is no risk of delamination (no film constitutes the sail), so durability will be very long. Finally, the sail will be very light due to the absence of film.
A membrane sail, how much does it cost?
Between the Dacron and the DFi, we are on a ratio of 1 to 3 for a mainsail and 1 to 4 for a headsail (for which the finishes are less important). This price difference is mainly due to the design office, research and development work on a membrane sail.
However, these figures should be considered with caution as a woven sail is not comparable to a membrane sail. Neither can satisfy the same program. In order to compare prices, different membranes or fabrics can be compared in parallel, but these two materials cannot be put in competition for the same specifications. It would be a bit like comparing a standard car and a Formula 1!
Can we design membrane sails for cruising?
In the choice of a membrane sail the designer takes into account two decisive elements:
- the navigation program
- the type of boat
" The more we will be on regatta programs, the more we will look for fibers with good shape retention (Kevlar), the more we will be on a cruising program, the more we will look for fibers that have a good resistance to UV (Spectra) ", explains Julien Gresset, from the Incidence Lorient offshore racing centre. " It is therefore quite possible to envisage DFi sails on a cruising yacht. "
The fibre plan is defined by the draftsman and the engineers of Incidence Technologies: it is a complex calculation table which allows the fibres to be placed in direction and quantity in response to the mechanical stresses of the sail during navigation, and which will define very precisely the nature of the fibres according to the boat's programme. Each membrane is therefore a unique piece made to measure.
Ronan Floch, Incidence Sails design office: " A set of specifications is defined and sent to Incidence Technologies. They look in their library of fibre plans for the one that best fits this specification and they work on it to adapt it to the specifications. This serves as a basis for work. This plan is then refined, tailor-made. "
Is it necessary to sail differently with a membrane sail?
Paul Meilhat has been working with the Incidence sailmaker since he has been racing in the Figaro Bénéteau and has been sailing with membrane sails for years, first classic, then filamentary.
He brings us the insights of top-level runners.
Paul, you've used classic membrane sails in Figaro Bénéteau, then sails (notably) in DFi since you've been racing in IMOCA: are there any particular precautions to take with this type of sail?
Paul Meilhat: With a membrane sail, the dialogue with the people who design the sail is very important, because you have to be very precise. The slightest flaw will show up. You have to work upstream on the triangulation of the sail. Because it will be more complicated to go back to a custom-made membrane profile than with a classic sail. There is a real dialogue with the draughtsman and the people in charge of production on the floor so that the skipper's constraints are taken into account.
Does a membrane sail adjust differently than a woven sail?
Paul Meilhat: The big difference between a membrane sail and a more traditional fabric sail is that the membrane does not deform. So you have to be in the shape of the sail as it was drawn. We're not going to be able to shoot it from all over trying to change its shape. It's going to have a stable shape no matter how strong the wind is. This has very interesting effects in the breeze since the trough will not deform, will not recede. So we're going to be able to wear a sail longer because it's stiffer.
We'll also be able to better control a twist.
On the whole, a membrane sail is tucked in a little less than a traditional sail because it will have a more important shape stability.
How do you maintain a membrane sail?
Paul Meilhat: I've been using membrane sails for a very long time and I haven't seen any difference with other sails in terms of maintenance. It mustn't be too salty.
On the other hand, you have to be very attentive to UV rays because membrane sails are made of Aramid which does not tolerate the sun at all: you must therefore systematically put awnings and covers even on the headsails which are rolled up.
On the other hand, for filamentary membranes, there is no risk of delamination: a large degradation parameter is removed.
