The booming expedition cruise sector is getting a little more crowded. Seabourn, the luxury cruise line owned by Carnival Corp., announced plans on Monday to build two 264-passenger expedition ships arriving in 2021 and 2022. The ships will visit Antarctica, the Arctic, and other hard-to-reach global destinations. They may have company. Expedition cruising is growing rapidly, with more than 25 ships on order, according to Cruise Industry News. New ships are coming from Ponant, Silversea, Hurtigruten, Lindblad — and now Seabourn. “The way I see it is that the expedition industry is where the river cruise industry was five or 10 years ago — just being discovered, with a lot more potential to come,” said Ben Lyons, CEO of Expedition Voyage Consultants, which advises cruise lines on planning and operating expedition sailings.