It's rare.

This quirky sail, which photographer Craig Greenhill of Salwater images capturedduring the fourth day of Audi Hamilton Island Race Week 2014, is called a parasail, or perforated spinnaker. Such sails were popular in the 1950s, but are quite rare today. The parasail design was thought to somewhat reduce draft and make the vessel more stable. However, parasails never gained popularity in sailing, as greater stability was achieved at the expense of heavier propulsion and loss of speed.