Crane meets with Volkan Yasif Dal and his two brothers, where Volkan finalizes the plan to escape the island.
Head to the specificed location on the map. The map is slightly deceptive - if you take the direct path, you will likely reach an area that simply leads to a dead end. Instead, you should head east and follow the coast instead.
When you reach the location, speak with Volkan, and push the submarine into the water.