Carolyn Dorothy: The First Diesel-Battery Electric Hybrid Tugboat
As can be seen from above image the hull of the hybrid tug appears identical to the other Dolphin class tugs it is working alongside in San Pedro Harbor.
However here the similarity ends, the engineroom contains the hybrid designed power units, their specification is listed below;
- Main engines - 2 x Cummins QSK50 main engines, each producing 1342kW at 1800 rpm, reduced to 270 rpm through a gearbox driving the props.
- Power generation - 2 x Cummins QSM11 generators, each producing 300kWe.
- Batteries – 126 x 12 volt, marine deep cycle gel lead-acid batteries.
- Electric drive – 2 x 746kW Electric Siemens Shaft Motor/ generators located on the output shafts, operated by clutches.
- Propellers - 2 x 2.4m dia, 4 bladed propellers incorporated in Azimuth Thrusters.
I have included a layout of the engineroom of the hybrid tugboat, (as I see it) and typical stern drive Azimuth Thrusters
Photo from http://www.thrustmastertexas.com
There are numerous configurations for using the hybrid engines; however the designers have selected four applicable modes;
1. Minimal Emission – power is supplied by the batteries for the normal ships services as when tied up. This mode is also used for short runs of 4 knots, powered by the shaft generator/motors. This mode is used 65% of the time.
2. Eco Cruise – this mode is used for barge work and typically uses both generators to provide power to the driveshafts via the shaft motor/ generators, and is used 13% of the time.
3. Mid Range – for up to 45% power, both main engines are used. This mode is used 15% of the time
4. Full Power – both main engines plus the two power generators are used in this mode, used 7% of the time.