The "Zeebrugge disaster" refers to the capsizing of the MS Herald of Free Enterprise on March 6, 1987. The ferry sank just moments after leaving the port of Zeebrugge, Belgium, en route to Dover, England. Specifically, it capsized about 1 kilometer (roughly 0.6 miles) from the shore, just outside the outer breakwater of the harbor. The ship sank in relatively shallow water, which resulted in the vessel lying on its side on a sandbar, half-submerged. The cause was a fatal combination of human error and design: the assistant boatswain had fallen asleep and failed to close the bow doors. As the ship accelerated, a "bow wave" entered the open vehicle deck, creating a "free surface effect" that caused the ship to flip in less than 90 seconds. Because it was so close to the busy port, rescue operations began almost immediately, but the freezing water and the speed of the capsize still resulted in 193 fatalities.