How Could the Fitzgerald Collision Happen?

From Popular Mechanics

How can two oceangoing vessels collide in the seemingly limitless expanse of the sea? That’s the question everyone has been asking since the U.S. Navy destroyer USS Fitzgerald was involved in a major incident with the container ship ACX Crystal. While the cause of the collision may not be known for weeks or even months, a former destroyer captain has written an article for War on the Rocks explaining just how difficult navigating ships at sea around one another can be.

Bryan McGrath, who commanded one of Fitzgerald‘s sister ships, USS Bulkeley from 2004 to 2006, explains how ships read one another at sea, trying to deduce the other’s intentions. The “rules of the road” for ships to avoid collision is well-known, but that’s where the car analogy ends. At sea there is no ‘road’ and ships approach one another from all directions, at distances that are far beyond what the naked eye can see. What’s more is that these ships do not stop or change course easily. As McGrath writes in War on the Rocks:

Big ships do not turn or stop on a dime. A 29,000-ton merchant vessel traveling at 15 knots takes a long time to stop or slow, and its turning radius is quite large. Using formulas from the ABS source cited here, the International Maritime Organization (IMO) standard for the container ship involved in this collision appears to be approximately 2.5 nautical miles to stop (at 15 knots) and over a half mile turning radius. The 9000-ton destroyer in question is quite nimble comparatively, but our automobile-infused understanding of last second swerves or the power of anti-lock brakes simply fails in this context. Decisions to avoid collision must occur far earlier and at far greater distances than in an automobile, and the longer that decision is delayed, the fewer options for avoidance will exist. In a car accident, the point at which maneuvers by either car will be insufficient to avoid the collision happen in milliseconds before impact, but that point is…

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