Comparative computational fluid dynamic tests, which used a standard ketch rig as found on a 56m Perini Navi, showed that for the same heeling or side force his Aero sail system produced over 140 per cent more forward force, which translates into the same performance with a much reduced sail area.
Since then, Šifrer has been working to further develop the concept and now has a "little Green Jet” prototype on the water. Based on the 5.5m hull of the successful Seascape 18 (voted Boat of the Year in 2010) with an 8m, all-carbon aero rig of his own design, initial sea trials by professional Slovenian sailors in the northern Adriatic have confirmed the concept’s ease of handling and performance.
“All the computer modelling calculations, scale model predictions and testing during eight years of development turned out to be very precise, as the Aero sail system is simple, efficient and easy to operate,” says Šifrer.
Aero rigs are not a new concept, and the advantages of unstayed rigs for short-handed sailing are well known. Normally they consist of a main boom and a fore-boom fixed to a mast, which is unstayed and mounted on bearings in the hull and deck. These allow the mast—and thus the whole rig and self-tacking jib—to rotate freely. Because the main sheet loads are less than with a conventional rig, aero rigs provide a safer environment for children and/or non-sailing guests, while the fact there is no standing rigging improves visibility and space on deck.
Advanced composites have much improved the potential for installing such systems on super sailing yachts and Maltese Falcon’s famous Dyna Rig is effectively a hybrid Aero sail system. Šifrer’s innovative concept draws on these same advantages, but employs a more stable and rigid wishbone mast structure.
“The pivoting mast is straightforward compared with those of the Maltese Falcon, which had free-standing masts, because our system is fixed at the top so there is less loading,” says Šifrer. “The lateral force is distributed between the two side pillars, so one is working in compression and the other in tension.”
A further bonus is that the system will likely appeal to motoryacht owners who are attracted by the romance of sail, but not all the hardware and technology that goes with it.
“The specific Aero sail geometry of our rig is perfect for the charter world or super sailing yachts of up to 100m with three to five masts,” claims Šifrer. “But the most important thing is that we have a boat that is completely free of blocks and lines, so guests can move around on deck with minimal risk. The boat is extremely simple to sail and software can be developed to do it automatically, even by iPhone if necessary.”
See The Superyacht Report issue 159 for more on rig developments.