We have just installed a Forte mainsail onto a Jenneau 53. It's a large sail so thankfully it was made from a one piece. molded material so that the weight is manageable in fact, that was the primary consideration for the purchase.
When we compared the weights of various 'cloths' here's how it stacked up.
Dacron 70 kg
Hydranet 65 kg
FORTE 45 kg
This is a cruising boat so the weight issue was not necessarily a ultimate performance one but rather a man handling one. If you've tried wrestling a heavy sail on a pitching deck, you might know what that means!
FORTE is the material developed by One Sails Italy during Team Prada's Americas Cup campaign. Team Prada worked with the University of Milan to come up with proprietary materials to give the Team and advantage. As a spin off from the program, One Sails carried on developing the technology to give us the filmless, no panels membrane known as FORTE.
FORTE is in fact 19 layers of differing materials that are laid over a mold and then heat/pressure fused to become one-piece. It yields a very high strength:weight ratio and because each layer is selected to serve a different purpose, it's resistant to UV and abrasion.
The great advantage of such a high-tech sail is the fact that the cross section shape that is designed into the sail remains intact over the entire life span of the sail.
In the case of Dacron (any woven fabric) the shape that id designed into the sail quickly fades as loads get placed onto the sail. This translates into erratic handling as the wind speed increases and in reality, Dacron has the shortest performance-life of all the cloths.
Panel-less sails have no panel seams not only does this create a really smooth wing-like surface but compared to a panelled film sail, there are no points where moisture can penetrate the structure.
A good aero-package isn't complete unless you look at the details. With the sail being molded as one piece on a mold specific for the particular model, the supporting battens are dialled in to stabilise the shape.
In this case, One Sails designers specify RBS battens to build battens for this sail for the model Jeanneau.
Even the sailmakers photo patch gets a new twist. In this case, the sailmaker has an app that can read all pertinent information on the sail. This includes date of construction and date of commissioning so that any One Sails loft in the world can look at the patch and know everything about the sail! In this case, some of the interesting information included "designed for 2-35 knots!"
We've been with One Sails for near on 10 years now. What convinced us to go with One Sails was the fact that we had our first One Sails VEKTOR mainsail intalled onto out boom and it never came off for 8 years.
Our primary concern was durability as we live on the Equator and effectively the sails live in a steam bath 24x7/365 days of the year. Previous to One Sails VEKTORS we had tried 3 big brand name lofts and pretty much suffered failures within a year and a half that solicited "we've never seen that before" responses! The problem here is the relative humidity is so high and in combination with high ambient temperatures, means that sails are subjected to steaming all the time. In the average film sails, moisture would enter the sail via the stitching on seams of the panels. Once it was inside, it would turn to steam as temperature was applied resulting in a failure. With the fused, filmless sails it's virtually impenetrable. The lack of panels means minimised sewing and therefore less opportunity for moisture to squeeze it's way in.
Honestly, we relayed our concerns to One Sails and were told "we've tested the material to 75 degrees without failure". Even as we installed our first set onto the boom, we sort of half believed it. After 8 years of fortnightly racing, coastal sailing, race training, beginner training classes, we are totally convinced as we experienced 0 failures in all that time. And our UV is in the extreme range!