A Star to Steer Her By
This is a young adult romance set on a sailboat in a tropical locale AND IT HAS A SCOTTISH HERO WHO IS ALSO A SAILBOAT GUY so really what else needs to be said? But I'll add that this book also features an aspiring-scientist heroine, some terrific conflict, and a deliciously tender romance. Also it's a great way to experience the sea via sailboat with no Dramamine required.