A Yacht is a large pleasure boat. There's no exact definition, but you wouldn't call a 15 ft motor boat a yacht or a 40 ft work boat. Any well maintained 30 ft plus boat that's not used for commercial purposes could reasonably be called a yacht.

Edited to add: The structure in the article is in my opinion, not a boat: Boats have a means of propulsion, (sails, oars, motor) this floating school is a barge.

"Barge" is a much better word; thank you.

As far as I know (which isnt that far), it's pretty well known that "things people build" + water leads to impermanence. Anything on the water continues to exist because of constant maintenance. This thing didn't look painted.