At an unveiling ceremony for the hybrid tug, named Carolyn Dorothy, Foss presented special awards of recognition to the ports of Long Beach and Los Angeles, and the South Coast Air Quality Management District to thank them for their support of the development of the Green Assist. To help defray the added costs of development and construction of the first hybrid tug, both the Ports of Long Beach and Los Angeles contributed funding.
|Hybrid tug propulsion system. Click to enlarge.|
Foss partnered with Aspin Kemp & Associates and their affiliate XeroPoint to develop the hybrid power management system. Compared to a standard ocean-going tug with large engines directly driving stern propellers, the Hybrid Assist uses smaller engines to drive motor/generators that charge a large battery pack. Thrust is decoupled from the engines.
The Green Assist Hybrid Tug is expected to significantly reduce emissions compared with the operating duty cycle of the conventional Dolphin tugs in San Pedro Harbor, including a reduction in NOx, particulate emissions, sulfur dioxide and carbon emissions. This exceeds the EPA’s Tier 2 emissions requirement for marine engines.
The hybrid tug design was awarded the EPA’s Clean Air Excellence Award for Clean Air Technology in 2008. Along with less pollution, the Hybrid Tug offers improved fuel economy and lower maintenance costs. It is also quieter than its Dolphin sister tugs, when operating on batteries that can be recharged using shore power.