There are plenty of boatbuilders in the northeastern United States continuing to build classic sailing yachts. Where Morris Yachts of Trenton, Maine, succeeds is in its ability to design classic yachts with contemporary appeal. In March, the 41-year-old family-owned shipyard debuted the latest design in its M-Series line of modern-classic sailing vessels. The M46 has an overall length of 46 feet and features two below-deck cabins. The yacht’s design, penned by the American naval architecture firm Sparkman and …