The New York Times, in an article full of impressive photos:
A conveyor that staff members call “the Cable Highway” moves the cable directly into Durable, docked in the Piscataqua River. The ship will carry over 4,000 miles of cable weighing about 3,500 metric tons when fully loaded.
Inside the ship, workers spool the cable into cavernous tanks. One person walks the cable swiftly in a circle, as if laying out a massive garden hose, while others lie down to hold it in place to ensure it doesn’t snag or knot. Even with teams working around the clock, it takes about four weeks before the ship is loaded up with enough cable to hit the open sea.