Interlake Steamship moves toward upgrading its fleet to energy efficient, more environmentally friendly LNG fuel. The company has announced that it has reached an agreement in principle with Shell to supply liquefied natural gas (LNG) to support Interlake’s conversion of its vessels to LNG as the main propulsion fuel. When converted, these ships are expected to be the first LNG-powered ships on the Great Lakes and among the first in the U.S. With a goal of converting the first vessel by the spring of 2015…