I first booked 4 adults and 1 child for this activity through Viator few weeks in advance. Since my other family member wanted to join this activity, I called Viator for availability and successfully added 4 more adults. We went to the dock for the activity, but the Hang Loose Boat Tour company told us that they didn't get any update for additional 4 adults. They also told that Coastguard wouldn't allow them to ride on their boat over the limit. So 4 of us had no choice but wait over 2 hours until the activity was done. The Viator ruined our family reunion trip that we planned for years.