To work on-board a superyacht STCW 95 is required which is a 5 day course at a cost of $1825 Australian dollars. There is a discount available if the chef course and STCW 95 are booked at the same time.
Superyacht Crew Academy has numerous other courses available including the VHF Radio licence course , another essential piece of paper work. http://www.superyacht-crew-academy.com/radio_certification_superyacht.html
Checkout this comprehensive website at http://www.superyacht-crew-academy.com/