It's not leaking. The dark area is a calm area caused by the ship acting as a wind break. The wind, coming from the north in this image, is blocked by the ship so it doesn't cause the ripples seen elsewhere. If you look to the north on the image you'll see a large grouping of smaller ships, some nested together, creating the same calm area in the lee of the ships.
Random useless trivia: This is the similar to the technique the Navy used to practice when they recovered sea planes in the open ocean. The recovering ship would execute a turn that placed it broadside to the oncoming wind. The sea plane would land in the temporary calm space created by the ship.
Sea - Shipwrecks 
Random useless trivia: This is the similar to the technique the Navy used to practice when they recovered sea planes in the open ocean. The recovering ship would execute a turn that placed it broadside to the oncoming wind. The sea plane would land in the temporary calm space created by the ship.