Rolls Royce said US regulators had given it the go-ahead to market a marine engine designed to reduce fuel consumption and emissions from ships.The engineering giant said the Certificate of Conformity bestowed by the Environmental Protection Agency would give it a head-start in the US market.The engines are already in operation on car ferries and coastal ferries in Europe, and are being installed on the world's first gas powered tugs to be used in operation for Norwegian oil company Statoil.President Neil Gulliver said the certificate was good news for the US marine industry because liquid natural gas as a vessel fuel was indisputably the best long-term solution for ship owners. "Our innovative vessel designsand gas-based power and propulsion systems help ship owners reduce through life costs and improve operational efficiency,while dramatically reducing harmful emissions and meeting strident future international environmental regulations," he said.