slip her cables

Captain Bogardis detected impediment of his vessel by the harbor master in the 'morn' because of questionable entries in the ship's journal..
At three A.M. Bogardis bent five elusive crewman to
'slip her cables', silently signal breathless, black-greased 'faceless mates' frozen on the yards aloft to 'come alive', make enough sail to breeze the harbor exit, fetch into an offshore freshet, thence to pierce the open sea's dastardly fog-shrouded black blanket of blackest, black void!