The default perspectives here are Alex in the Theatrical Cut and Fliss in the Curator's Cut; if either of those characters are dead, the role of player character will be passed onto someone else. Follow the other characters along the deck, taking note of a crate off to the left where Secret #50: Anti-Aircraft Shell Casing can be found. Follow the others to the radio tower, taking a right at the end of the path to find a cabinet that can be opened for Secret #3: Gas Mask Instructions. Across from the cabinet is a prompt to climb up. After doing so, find the first door that can be interacted with and press the prompted button repeatedly to force it open.
Inside, follow the others through the doorway and take a right to find Secret #42: Ship's Logbook on a table. Flipping through the pages here is not only essential for Secret #42, but to discover the ship's full name, which will trigger an achievement/trophy when Alex mentions it later. In the same room, walk along the wall to the left to eventually find a Picture, Loose Cannon, on the wall. Walk through the doorway nearby and follow the path to find Secret #6: Nautical Chart on the wall. Before entering the next room, walk near the camera to find Secret #10: Navigator's Notebook on a table. In the next room, pick up Secret #29: Radio Operator's Final Message on a table near a corpse. Be very careful here, as approaching the radio will trigger the next scene and lock you out of obtaining it.
After approaching the radio, mess with the knob until reaching the right frequency. When given the option, choose to be instructive. When Brad volunteers to leave, if playing as Alex, make sure to be encouraging. These choices will allow you to obtain the achievement/trophy for the ship's name in the next chapter.