There were a total of three ghosts ships that were on the tail of the old rotten ship that the Elites were on.
Although the parameter to clear was to survive for 30 hours in the dungeon , without the ship , it was impossible to survive for more than 5 minutes in the ocean.
This was not because of monsters or other creatures that would attack you ..... No , it was because the water was ice cold and would give you a freeze countdown when submerged.
About 3 minutes into the countdown you will be unable to sustain muscle movement to float , as your body will recede the blood towards the vital organs .... From then on you drown , for a maximum of 2 minutes can you survive without oxygen , as you pass out after that because of lack of oxygen and the cold.
All this happened if you survived for the 5 minutes , mostly you were killed by some sharks or other sea creatures lurking as soon as you enter the water.