Around its equatorial middle, our planet is rife with exotic atolls and palm-fringed isles adrift in cerulean seas. But there’s a reason the yachting set has always counted the Caribbean among the world’s best destina- tions for setting sail. The proximity of its sand-spun islands — both to one another and to the mainland beaches — means that a relatively short vacation itinerary here can include several culturally diverse and exciting destinations. And when your mode of transport moves from the sea to the sky, exploring the…