At the end of "Murder in the City", choreography indicates the ship beginning to rock violently as actors slide and roll across the stage. Then "water" (blue light with accompanying sound design) crashes across the deck and there's an ensemble reprise of "Lord Lay Your Hand on My Shoulder" alongside an awesome slow motion choreography of crew falling / struggling against the turbulent waters.
Movements resume normal speed, lights flash on a dim stage and most cast leaves the set quickly (most take the stairs down/go out the back) except for Big Brother and Little Brother who have additional sequence struggling to stay aboard. Then, as the transition begins, they slip off the front of the set (quickly and in dim light - not meant to be noticed), music mounts, and the deck begins to swing upwards. Two rigging lines snap, and the entire deck hinges up at ~70 degrees from the floor. Simultaneous, the lifeboat prop rise from below the stage and the surviving four climb in. This all happens in basically the dark and most audience members will be too focused on the ship deck rising up to notice.
The lights come up on the lifeboat and it begins to rotate as the Mate narrates that 6 days have passed.