Representatives from Seatrade Cruise Global, an annual business-to-business convention that attracts more than 11,000 attendees from over 113 countries, has invited two top executives from new South Florida-based cruise brands to headline a panel at the event. The panelists: Tom McAlpin, chief executive officer of South Florida-based Virgin Voyages, an adults-only cruise line launching in Miami; and Douglas Prothero, the managing director of Ritz-Carlton Yacht Collection, a new luxury brand based…