North Sails 3Di | english version

We’re seeing those very distinctive grey sails showing up on some of the TP52’s, on a few RC44 and soon on both VO70 Puma and our J/109 Blur. It’s the new 3Di technology from North Sails, that slowly is turning into a commercial product.

I was invited to Minden, NV, to have a closer look and to talk to the production and engineering staff. Here’s a short report.

You might recall the “black sails” that Alinghi tested in 2007? They didn’t have enough time to get them up to speed, but the swiss understood the technology to spread individual fibers of PBO and how to make a sails out of that.

At the same time the guys at Cuben Fiber figured out how to do this with Dyneema, but had difficulties with carbon. When North Sails bought the two technologies, they could be used to combine carbon and Dyneema fibers in tapes like the one above. Those tapes are now the the basic component of 3Di.

The whole process begins with untwisted yarns of carbon, aramid and Dyneema.

They’re run through a machine, dubbed the “Pregger”, which spread the individual fibers. Here Dyneema yarns are fed into the machine.

Carbon, Aramid and Dyneema fibers are all spread on this machine, with different paths and technologies for different materials. Josh Marhevka ensures that the fibers are coated with a thin coat of thermoset adhesive to hold them together, both as a tape to build the sail and to consolidate all the parts forming the final sail.

The fibers are placed on a backing paper, dried, rolled up and cut into narrower-widht rolls. Depending on the mix of fibers, the tapes can be run two or three times through the machine.

Here we see the entire machine.

Holly Jensen continuously check the weight of the material. As a sails are built of many layers of tape, the tolerances are very small in order to keep the overall weight down.

The tape-laying heads goes back and forth over at flat floor to lay out all the tapes according to the design. It collects the backing paper and cuts the tapes.

Here is a completely new version of the tape-laying head that were taken into production when I was there. Small adjustments are made continously and both engineers and software developer sits on the second floor of the 3Di building.

Here’s the top section of a main to a Swan 601. North have chosen to produce several smaller parts that is easier to handle when moved to the mould. They also get better utilization of the equipment by having several smaller areas rather than few large ones. The layout software makes it easy to seamlessly connect the different layers of tape on the mould.

Tapes are sticky enough to stay together when the sail is being handled, but not so sticky that they can not move when it’s shaped on the mould.

Here’s a good view of the different layers of tape. At the bottom an outer grey layer, then internal layers of tape before the upper layer on the other side. There are 20 different tapes, each with a different set of characteristics.

The sail above seems to be very similar to our new sails:

  • The grey outer layer: polyester non-woven outer surface over dyneema bonded with thermoset polyester adhesive with UV absorbers and colorant.
  • Black tape with aramid: Carbon and Dyneema filaments bonded to X-Aramid scrim with Polyester thermoset adhesive and UV absorbents.
  • Black tape: Carbon and Dyneema filaments bonded with thermoset polyester adhesive and UV absorbents

Let’s look at the components.

  • Carbon fibers are stiff and resists both tension and compression very well, but they are fragile and individual fibers can not be folded
  • Aramid fibers are strong and resists both tension and compression. Not as fragile as carbon fibers, but UV-sensitive.
  • Dyneema fibers are resists tension, but not compression. Dyneema is very durable and flexible,

So, by combining these fibers, the material can get exactly the characteristics needed. 100% Dyneema was soft and easy to handle, but crumpled without tension. 100% carbon was nice and strong but delicate and difficult to handle. Right now there seems to be an optimal mix of between 50/50 and 70/30 carbon/Dyneema or aramid/Dyneema. But this changes continuously based on feedback from the real world.

The picture also shows that some of the tapes have a scrim with aramid at -45/90/45 degrees. It gives structure stability to the tape itself, and reduces the number of tapes needed.

Overall there are about 20 different tapes in production, and the sail design software uses them in different layers to build the sail. Above is a part of our new jib.

While it’s a good thing to be able to build sails with just the characteristics you want, it might be difficult to explain to customers. So North has divided 3Di into categories (might change over time):

  • 3Di 870 Carbon/Dyneema, club racing
  • 3Di 880 Carbon/Carbon, TP52 or Melges 32 (containing less Dyneema)
  • 3Di 670 Aramid/Dyneema, VOR or Open 60 who can’t use carbon.

(6 = aramid, 7 = Dyneema , 8 = carbon)

The pieces are transported to the same moulds that is used for 3DL and the edges are interleaved together as much as they would be if the tapes had been laid all the way across the joint. The actual shape is achieved when streching the tapes on the mould and then when heat is applied. Here’s a 3Di layed up on thge mould just before consolidation.

The whole sail is then sealed in a vaccum bag and all layers are consolidated with heat into an almost isotropic structure (resistant to force in all directions). There’s a distinction betwween lamination (bonding materials with different properties, as in 3DL) and consolidation (bonding of materials with similar properties, as in 3Di).

The above software is used to control both the path and heat during consolidation of our jib.

Gabe Testa is one of our developers who work with the software behind 3Di. Here’s a view of our jib.

Here we can clearly see the different layers of tape.

There are many advantages to building sails this way. Naturally we get stiffer sails that keep their shape better and have stability in all directions. In addition, the individual fibers do not absorb water. All sails with yarns in the load direction absorbs water through capillary action.

At this early stage, there are of course disadvantages with 3Di. Above all, they have been sensitive to wear (spinnaker ring on the mast, backstay, …). There have been some breakeges. Typically in winds 4-5 knots above the range that the sails were designed for. Since they don’t change shape, and they’re still fast and looking good they tend to stay up longer.

UV is of course a huge problem for aramid. Individual aramid fibers (as in a 3Di sail) can be destroyed after a day in the sun This is solved with a thin coat of paint.

Trimming a 3Di will require a bit more tuning in light wind, but the sail will be more stable and require less adjustment as the wind picks up. More on this as we get our new sails.

After the sails have consolidated and hardened, they’re finished on the floor. As batten pockets and reinforcements are already in the sail itself, they require less work.

Here’s a completed 3Di sail for Puma. Richard “Scoob” Kiff (in blue T-shirt) discusses with Jeff Neri. Scoob works for Puma and helps out with the details. He also worked for Oracle in the last AC.

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