IN THE EARLY TO mid-1980s, when the word mega-yacht came into fashion, 100-footers elicited second looks. A decade later, yacht designers stood amazed at requests for 150-footers. These days, private yachts twice that size—and larger—are slipping into the water, leaving even jaded professionals astonished. ¶ It’s the era of the giga-yacht. ¶ A buzzword, really, giga-yacht loosely defines supersize superyachts. Benetti recently began using the term for yachts exceeding 100 meters, or about 328 feet, in length. The size range is a new focus for the shipyard, producing noteworthy results. From December 2018 through this past April, it launched not one but three of these yachts—its first three. ¶ Given that just one custom yacht, regardless of size, requires years of planning, the act of building three simultaneously requires an…