Fellow Chanel College student Luke Hempleman, 15, had completed a voyage aboard the Spirit of New Zealand in July and classmate Calan Robertson-Bennett, 15, sailed as a trainee crew member the previous month.
Mr Hempleman said the ship held berths for up to 40 apprentice crew members at a time and Day nine was the voyage climax, when the seasoned crew steps back and trainees took the helm.
Mr Hempleman said trainees appoint the Day nine crew by vote and the muster includes a captain, a first, second and third mate - the second mate doubling as navigator - an engineer, chef, four watch assistants, and two leading hands.
The friends' accounts of their journey, tales of swimming with dolphins, and the positive post-voyage changes in their outlook had more than piqued the interest of Ms McCann in boarding the boat herself, she said.
"Their stories were just amazing, and it does change you. I've noticed that in Calan. Sometimes I get a bit of social anxiety and going on a ship like that with a whole lot of people I don't know - it's a little daunting at the moment - but once I overcome it, I can move on," she said.