Sixteen is often the age where you start dreaming of striking out on your own, of trying something just a little bit dangerous—though you still want to know that your parents have your back if you fall. That’s the appeal of True Spirit, a movie based on the real-life adventures of Jessica Watson, who at age 16 became the youngest person to sail around the world solo. Directed by Australian filmmaker Sarah Spillane, the picture is appealingly breezy, though it does have its share of tense moments...