While so much attention will soon be focused on the trickle-down of design lessons learned from the IACC class competitors in the America's Cup, there is a wealth of knowledge still waiting to be mined from fast mono and multihulls. One example of this at work already is the effort currently being made by Ben and Eric Hall of Hall Spars to develop mainstream, easy-to-use but high-performing unstayed and rotating spars. They've dubbed their latest efforts the Blackwing project, an oblique reference to the U.S. Air Force's SR 71 ultra high-flying spy plane, and also a descriptive term for their foil-shaped carbon-fiber mast.

According to Eric Hall, the idea came about two years ago, when he and Ben realized that with modern composite materials and the spar construction techniques they'd developed at Hall Spars, the virtues of a rotating spar could be realized on a modest-sized, high-performance monohull. Rather than go through the endless and costly trial-and-error method of determining the right engineering qualities of this spar concept, designer Scott Ferguson was quickly enlisted to help with the computer modeling of the mast's behavior.

"We certainly knew quite a bit about how to engineer a conventional stayed carbon mast through our experience with numerous offshore and one-design classes, but this presented a unique challenge," said Eric. A balance had to be struck between the size and shape of the spar, how it would enhance the effective airflow into the mainsail, and what stiffness and weight to achieve — all the while bearing in mind that this ultimately had to be a concept capable and practical enough for series production.

To speed up the process of data acquisition, test panels were built and placed in hydraulic jacks to measure stiffness and buckling loads for different tube shapes, sizes and reinforcement designs. Another important consideration was how to anchor the spar on a production-built boat in such a way as to allow it to rotate and not destroy either the boat or itself in the process. For mounting Blackwing into a J/90, the region of the cabin house around the partners was reinforced with radiating gussets that taper away from the bearing assembly mounted at the partners. At the mast step a simple socket lined with self-lubricating plastic was devised, where the trailer ball mounted on the butt end of the mast would sit when stepped.

The Blackwing spar rises over 1m taller than the conventional J/90 spar, and is several kilos heavier, despite not having spreaders or any standing rigging, save for a Vectran headstay to support the jib luff, and a set of Vectran running backstays. These adjust on a simple 2:1 system to help reduce headstay sag and support the spar downwind when the large masthead asymmetrical spinnaker is set.

The promise of enhanced performance due to greatly reduced windage has translated well from theory to reality, as the prototype has outperformed many other boats of its size in races around Rhode Island, earning repeated reductions in PHRF rating. The Blackwing project is currently into its third generation of spar design, with a new section in the works that is nearly 0.5 meters in chord length, promising to deliver even greater efficiency. Now that the Young America hardware has been sold, it's been conceded that some features of the Blackwing were incorporated in the large chord spars built by Halls for USA-58 and USA-53, spars rumoured to also be capable of moderate torsion.