So I was just browsing Wikipedia and came across this
In the wake of the September 11, 2001 attacks, there have been concerns about the security of LNG shipments within Boston Harbor, and increased fear of terrorism. Because of the location of the LNG terminal in the Mystic River, tankers traveling to and from the facility are forced to pass directly offshore of downtown Boston. During their voyage through the harbor, they are protected by a security zone that extends 2 miles (3.2 km) in front of the vessel, 1-mile (1.6 km) behind it, and more than half a mile on either side. This zone is enforced by escort vessels provided by the Coast Guard and State Police. The Tobin Bridge is closed as the escort passes under it, and boating is forbidden within the security zone.
I'm new to the whole sailing thing, and I've only been around Boston harbor for a few weeks, but it still surprises me this is the first I've heard of this. It doesn't seem to be noted on the charts, nor in the LNM, and no one in the know has mentioned it to me. It sounds like if an LNG carrier is coming in, pretty much the entire Charles would be blocked. I'm glad I didn't accidentally go sailing when this was happening! How do they notify mariners where/when to stay away? How often do LNG carriers come in?