赛艇 refers to both the sport of rowing and a racing boat (also called a shell). When used as a verb meaning 'to row' or 'to race a boat', it is a separable verb (离合词): you can insert measure words, duration, or complements between 赛 and 艇, as in 赛过一次艇 ('rowed once'). The noun form does not split. The word is common in sports contexts.