Carbon emissions at sea have received more attention over the last decade. Ports, especially, can have a negative impact on air quality in the populated areas that surround them. The many emissions sources at ports include ships, trucks, trains, and cargo-handling equipment. Harbor-crafts also contribute a significant portion of total port emissions. These include tugboats, ferries, fishing boats, and dredge vessels. Recently, the Ports of Los Angeles and Long Beach have started using a hybrid electric tugboat. A new study by the University of California (UC) Riverside has shown that this has been effective at reducing emissions.
Tugboats are typically powered by marine compression ignition engines. The engines are built to be extremely powerful relative to the size of the vessel. Larger tugboats used in deeper waters have power ratings up to 27,000 horse power. They can have a power:tonnage ratio of up to 4.5, similar to engines used in locomotives. These engines typically drive the propellers mechanically rather than converting the output through electric motors, as is done on trains.
The massive engines can consume large amounts of fuel and produce harmful emissions full of diesel particulates. This has made the Ports of Los Angeles and Long Beach the largest contributors of air pollution in the South Coast Basin according to the California Air Resources Board (CARB). Pollution from the diesel-powered tugboats and other port emission sources has caused negative health effects on the surrounding population, including cancer and respiratory illnesses.
Now the Ports of Los Angeles and Long Beach, the largest container ports in the nation, are home to the first and only hybrid electric tugboat in the world. Named the Carolyn Dorothy, it runs on four diesel engines and 126 batteries. It was financed by the two ports and the South Coast Air Quality Management District to the tune of $1.35 million. The vessel was built by Foss Maritime, based in Seattle, and began operational duty in January of 2009.