Use a rope arrow to the object on the left side of the ship to automatically put the rope ascender to good use. Drop down the hole and move through the hall until you reach Sam's cabin. [150 XP]. Inside is [DOCUMENT - #4 ENDURANCE CREW (SAM: ADVENTURES WITH LARA)]. There's a Solarii guard at the end of the walkway; after the conversation, move back through the walkway and shoot him in the head as he approaches. There's another guard in the other area below, so dispatch him as well. Soon enough you'll reach the flooded part of the ship. [250 XP].
When you find Alex, pull the device on the roof towards the door. The path is blocked by a large pipe, so you'll first need to head up to clear it out of the way. To do this, move around the left side of the device and hang from the broken ladder to move the device. From here, pull it away from the door with a rope arrow. Lastly, climb the right side of it (the ladder that's not destroyed) to reach the opening in the ceiling. Move through and kick the pipe down. Pull the machine away from the door once, then climb the broken ladder to get it in the right position. From here, one more pull will move the hook into the electricity wires blocking the door. A last pull away from the door clears the way to Alex. [100 XP].
A scene plays [100 XP], after which you'll have to quickly run through the hall, jump towards the rope and press X or Square to use the rope ascender. Afterward, climb the crates at the front of the ship and climb the rope (use the ascender to speed this up) to backtrack through the area. [100 XP]. At the day camp, use the rope ascender to pull down the rope block from above the doors to reach the lower area.
[DOCUMENT - #3 WARTIME INTELLIGENCE (SCIENTIST: SECRET OF THE ISLAND)] is automatically received after the scene. Open the door with your axe and you'll be back in the main hall of this building. The door to your right (in the northeast corner) can now be opened with the rope ascender. Climb the nearby crate to reach it. Inside this room is a [SALVAGE BAG], as well as the [RELIC - #2 ANCIENT COINS (100 MON COIN)].
Head back the way you came (through the cracks in the wall), then destroy the heavy barricade in this bunker room you previously had to leave alone. On this platform is a [RELIC - #3 ANCIENT COINS (PORTUGUESE TIN COIN)], a [PLANT], and the complete [TREASURE MAP] of the area on some sandbags near the door.
BACK AT SHIPWRECK SHORE
Destroy the heavy barricade to your immediate left as you return to shipwreck beach to find an [XP BOX] and a rope leading up. There are three Solarii guards here. Wait for them to finish conversing, then dispatch the one closest to Lara. Take out the other two with a series of arrows (but note that they have headgear so don't bother with headshots). You've also discovered 'The Grotto' day camp. Before heading all the way back, first drop down the adjacent lower platform to the east and search it for a [GPS CACHE].
After this, return to the Endurance crew via the ropes to view a scene. [400 XP]. Use the camp to get [DOCUMENT - #8 LARA'S JOURNALS (THE PROMISE)].
Drop down behind the wooden crate and overheat the Solarii guards conversing. One of them is a true giant in the full sense of the word. Definitely hit him with a powerful arrow in the head as he returns. Quickly defeat the other two Solarii guards with shotgun blasts, then keep your distance as you keep hitting the giant with grenades. If you run out before he dies, tough luck; you'll have to dodge his blows while hitting his head, preferably with the shotgun. You can find [SHOTGUN SHELLS x2] and [RIFLE AMMO] on this deck. Move in for the finisher (Y twice, or Triangle twice) after softening him up. After the fight you receive the [ROPE ASCENDER], which helps destroy heavy barricades.