摆 here carries its older sense of "to row, to swing back and forth" (as oars do) —
摆渡 = "to row across." Common compounds:
摆渡船 ("ferry boat"),
摆渡人 ("ferryman"). The latter is also a famous metaphor in Buddhist-flavored writing for someone who guides others through life's hardships, popularized by Zhang Jiajia's novel 《
摆渡人》 (Ferryman, 2013).
