Trickle Down Theory: The Engineering Reality Show!

In the past year alone Doyle Sailmakers has faced the engineering challenge of building the sails for the 246-foot Mirabella V, the world’s largest sloop, as well as the 285-foot Maltese Falcon, which has a DynaRig consisting of squaresails on three freestanding carbon spars. The engineering challenges of these two mega projects could not be more diverse, yet both have and continue to have a great impact at how we look at and manufacture all our sails.

Meeting the Challenges of the World’s Largest Sloop

Engineering - Mirabella V sails

Mirabella V

On Mirabella V everything had to do with the sails being so much larger than any that had ever been built. The mainsail alone is three times bigger than the previous world’s largest mainsail! The loads are proportionately as large. As the decision was made early on to forego a rollboom, having the sails three times the weight was not an option. A much lighter fabric that could withstand the enormous loads needed to be developed and so Doyle developed OceanWeave®. OceanWeave is a woven Vectran x Vectran fabric that does not require film to stabilize it. The fabric that made up Mirabella V’s main was only 16.1 SM-oz (20.3 ox/yd2, which is lighter than many of the fabrics used on sails 25% the size of MV’s main). The fabric that made up her largest headsail, the UPS, was 8.0 SM-oz-10.1 oz/yd2. OceanWeave!

Mirabella V's Segmented Sail Section

Mirabella V's Segmented Sail

Despite being as weight-efficient as it was, the size and weight, as well as it being a full-battened mainsail, meant that it would be impossible to construct Mirabella V’s main using normal sail manufacturing techniques. Thus, the Segmented Mainsail was born. The Segmented Mainsail allowed the sail to be made in six separate pieces (the top batten was not a segmented batten, but slid into a pocket), connected by the battens that served as connecting hinges. This construction method also allows MV’s main to be serviced in separate segments as needed.

Mirabella V's Spring Battens

Mirabella V's Spring Battens

With battens as long as 80 feet (25 meters), breaking battens had to be avoided at all cost. The fact that the battens hold the sail together made this even more imperative. The Doyle Engineering Department worked with Ted Van Dusen to design extremely resilient battens as well as to develop the compression springs at the inboard end of the battens so that when the battens that overlap the backstay by a whopping 7.5 feet [2.3m] accidentally snapped through between the back stay and the mast they would not break. While it was intended that this would be avoided as much as humanely possible, on the very first setting of the main a 30-degree wind shift that came in at 200 feet off the water (while the wind direction was still the same on deck), tested the Compression Spring Battens to their core—and they passed! The Doyle Engineering Department not only designed the batten end fittings but manufactured them as well.

Soft Corner on Mirabella V

Soft Corner on Mirabella V

After having witnessed the damage that a four- or five-pound leech reef block can do to a sail, when the originally designed reef blocks arrived at the loft weighing 76 pounds we realized we had another challenge. So the Engineering Department took a coffee break and designed the Reefing Donut. These easily removable donuts weigh in at 24 pounds. They could have been lighter but we wanted to maintain the generous 10-inch diameter for the line to bend around as well as have two independent Vectran line attachments. While not invented for Mirabella V, the manufacturing of her sails would have been impossible without the highly refined, integral Soft Corners (first developed for the J Class Velsheda) that provide the strongest possible corners without the needless build up of thickness and weight.

Dynamic Solutions to a Mega-Size DynaRig

DynaRig profile of the Maltese Falcon

Maltese Falcon's DynaRig Profile

The 30,000 square feet of sail area in Maltese Falcon’s three masts is divided into 15 sails (five per mast). The challenge for these sails is that they are stored inside the mast and are deployed integrally into the yardarms, so that when all five sails are out at once on a mast they form a continuous wing. To accomplish this deployment and maintain the desired shape and limit the loading, these sails needed to be constructed to a precision in 3D not demanded by any other rig. Specialty design and paneling programs have had to be employed that go well beyond our normal, refined sail design software.

The latest in finite element analysis for sails, Relax, confirmed our back-of-the-envelope calculation that the best Dacron fabric, with appropriate plying, could handle the loading of the individual sails. Utilizing fabric that would give a bit would lessen the loading on the highly-loaded upper and lower grooves and thus this choice had other significant advantages as well.

As the entire sail, corners and all, need to furl inside the mast there is no room for corner rings or blocks of any sort. There are conditions where the loads generated by this 285-foot vessel will to be borne by a single sail in gale conditions! Thus, the world’s toughest bolt rope needed to be developed. It has been produced from a specially constructed 10 mm Vectran bolt rope by Yale Cordage and inserted into a specially woven Spectra x Spectra bolt rope. This same technology is now being utilized in our bolt ropes for rollboom mainsails.

In summary, detailed load analysis run for both Mirabella V and Maltese Falcon, along with the parsing of the problems we faced in each of these projects, has opened Doyle engineers’ eyes to better solutions for fabric construction, batten construction, batten fittings, rollboom luff tapes, and confirmed the importance of our integral Soft Corners.

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