Mastering the A sail
Though asymmetric spinnakers date as far back as 1865, credit Australian skiff sailor and designer Julian Bethwaite with the invention of the modern asymmetric, which he tested and developed on his Australian 18 designs during the 1980s. Bethwaite needed a spinnaker with a long luff and flat leech on either gybe. This would enable crews to sail the skiffs tight apparent-wind angles without collapsing the chute or sacrificing the sail power they needed to reach high speeds off the wind. That the sail, with its fixed tack and single sheet, simplified downwind sailhandling was an added bonus.
Twenty years on, the asymmetric spinnaker has developed into a versatile downwind sail for a wide variety of performance and cruising boats. Before boatbuilders could introduce the spinnaker on their racers, they had to devise a system for getting the sail away from the blanket of the mainsail while sailing on a low reaching coursenot a problem on a skiff, which sails downwind at near-upwind angles. A common solution for this is tacking the sail on a retractable bowsprit; the J/105, in 1991, was the first to reach the masses with this configuration. To make the sail more versatile downwind, it is designed to be projected to windward of centerline, which helps a boat sail lower reaching angles.
Though it requires a small number of crew to handleit has only one set of sheets, and in most cases no spin polecompared to a symmetric spinnaker, an asymmetric chute still needs to be trimmed right when sailing a straight line and during maneuvers. To demonstrate, I went sailing with Dave Flynn of Quantum Sail Design Group in Annapolis, Maryland, and worked the 960-square-foot asymmetric on Rum Puppy, a J/105. The results were some tired hands, a few rips in the sailcloth, and the following photo guide to sail trim.
Ease the spinnaker sheet until the luff of the sail breaks. Trim. Ease it again, trying to maintain a slight curl in the sail. Its that simple, but only if the sail is set up right.
More than a control line you pull and cleat, the tackline is one of the keys to a well-trimmed spinnaker. Dave Flynns rule of thumb for a sprit boat, such as the J/105, is to ease the tackline if the luff of the sail is no more than 10 percent longer than the straight line from head to tack. This will help project more sail area to windward, allowing the boat to sail deeper angles (more than 135 degrees apparent) more effectively. As windspeed drops, lower the tackline and sail tighter reaching angles.