With its low nose, pronounced feature lines, and carbon-fiber side air intakes, the Frauscher 747 Mirage (frauscherboats.com) evokes a supercar, and it performs like one. The most powerful of three engine options enables the 24.5-foot cruiser to reach a top speed of 56 knots. Frauscher, an 88-year-old builder based in Austria, offers the 747 Mirage with a closed- or open-bow configuration. The latter, called the 747 Mirage Air, can accommodate more passengers because it includes bench seats at the bow. The …