Challenge. . .
. . . of trimming the sails
correctly for the wind
. . . of finding your way into a new port without running aground.
. . . of getting a badly needed repair part a place far from civilization.
. . . of making do with what is at hand when unsuccessful with the previous challenge.
. . . of not becoming bored on the 5th day of a long passage
. . . of getting accurate weather
. . . associated with venturing out having failed to overcome the previous challenge.
Maybe not so much the challenges themselves but the gratification of meeting them - but that would change my word and mess up this post!