A fathom is six feet, so the boatman who says in Telemachus that "There's five fathoms out there" is indicating thirty feet of water in the outer reaches of Dublin Bay where it gives way to open ocean. (Thornton observes, "I have seen several maps of the Dublin Bay area which include a 'Five Fathom Line.'") Somewhere out there the body of “The man that was drowned” on June 7 is being pushed about by the currents and swelling up with gas, and folk wisdom holds that it will surface in “nine days.” Within these realistic details lurks an allusion to Shakespeare's The Tempest that raises metaphysical questions about life after death. 

JH 2011

Sea nymphs viewing the body of Ferdinand's father, in a painting by Edmund Dulac. Source: library.wustl.edu.