Old English seglinge, "act of one who or that which sails," verbal noun from the source of sail (v.). Gradually coming also to mean "the art or rules of directing a ship." Figurative use of smooth sailing for "easy progress" is from 1840.
Yes; I must press on this marriage; Georgina has not wit enough to manage him—at least till he's her husband, and then all women find it smooth sailing. [Bulwer Lytton, "Money: A Comedy in Five Acts," 1840]
updated on November 08, 2021