Duck Boat Safety Enhancement Act of 2021 This bill sets forth requirements related to the safety of amphibious passenger vessels. The U.S. Coast Guard must implement regulations related to the safety of amphibious passenger vessels, including during severe weather emergencies. The Coast Guard may require operators of amphibious passenger vessels to provide reserve buoyancy for such vessels through passive means, including watertight compartmentalization, built-in flotation, or other means, to ensure that such vessels remain afloat and upright in the event of flooding, including when carrying a full complement of passengers and crew. Additionally, the Coast Guard must implement interim safety policies or other measures to require operators of amphibious passenger vessels operating in U.S. waters comply with certain requirements, including to remove the canopies of such vessels for waterborne operations, or to install in such vessels canopies that do not restrict either horizontal or vertical escape by passengers in the event of flooding or sinking. The bill also sets forth requirements for vessels that are not in compliance with the regulations and interim safety policies.