The worldwide fleet of large power catamarans just keeps growing. Indeed, StellarPM, the Vietnamese builder, just introduced a new line of luxury explorer power cats that are designed to be as much as home in the fjords of Norway as they are cruising around Sardinia and Corsica. StellarPM now joins the ranks of builders in Europe, Turkey, Australia and other parts of the world who have been launching big, luxurious power catamarans lately. And expedition or explorer yachts are a growing subspecies in that category. There are two yachts in the new StellarEXP fleet, a 32-Meter (about 105 feet), and…