Disasters happen when you deconstruct a sailing vessel. Remove planks from the hull, realign the rudder, place too much cargo in one end of steerage, and the sturdiest schooner will capsize in frigid, choppy waters. As regards Jerome Kern and Oscar Hammerstein II’s Show Boat, a quantum leap in the evolution of Broadway musicals, seaworthiness was an issue long before director David Herskovits undertook his audacious makeover. It’s not that Show Boat leaks, exactly: the 1927 stage megahit led to...