Semester at sea for high schooler

We have a 15 year old , Hugh Kane , who is one year ahead on school credits. Our family has been planning for a semester abroad for him before he attends university or tech school. We started planning and saving 8 years ago, and since he is a watersport champion the prevailing opinion is to be on a school linked traditional sailboat, exploring and learning.... for example, one school offers 4 high school credits per semester while stopping at many countries around the Mediterranean

Anyone have direct experience with such programs?  If so, could you help by details about the semester?  I have been reading reviews but having a Permies opinion could be grand