A new fleet of tugs has hybrid propulsion to cut fuel and maintenance costs and reduce emissions
Great Lakes Towing Co is seeing 30-50% fuel savings from its investment in the hybrid propulsion tugs it is building at its own facilities.
This North American tugowner is investing in a fleet of new ice-breaking tugs for cargo transportation and harbour towage at its shipyard in Cleveland, Ohio. These are replacing vintage tugs, some of which have been operating for at least 50 years, said Great Lakes Towing president Joseph Starck.
These new tugs are built to a Damen Stan tug 1907 Ice design with 30 tonnes of bollard pull, overall length of 19.5 m, breadth of 7.3 m and shallow hull depth of 3.3 m.
Great Lakes Towing operates more than 30 tugboats on the US side of the Great Lakes, from Lake Superior to Lake Erie, operating from 12 ports from Duluth (Minnesota) to Buffalo (New York). The total group also consists of Great Lakes Shipyard, Tugz International and Soo Line Handling Services.
The towage business assists ships in harbours, transports break bulk and project cargo and offers barge transportation and logistics services on the Great Lakes, with transhipment opportunities to the Mississippi River system, Canada, and other seacoasts.
Great Lakes’ largest investment involves building its hybrid-propulsion tug fleet. “We have started the sixth hull of a series of 10 tugs,” said Mr Starck during Riviera Maritime Media’s Hybrid and electric tug viability: the future’s bright webinar, on 3 September.
“We wanted to develop the most cost-efficient system possible”
This sixth tug is scheduled for delivery in Q2 2021. Wisconsin was the fifth in a series of ice-class tugs, completed in Q2 2020. The other tugs in the series – Cleveland, Ohio, Michigan and Pennsylvania – have been operating since 2019.
These newbuildings are powered by two MTU 8V4000 diesel engines, compliant with US Environmental Protection Agency (EPA)’s Tier 3 emission requirements, driving 3-bladed Kaplan style propellers in Kort nozzles.
They each have two John Deere/Marathon generator sets and a hybrid power system supplied by Logan Clutch Corp and installed by Canal Marine & Industrial.
Mr Starck explained the company’s strategy for modernising its fleet and cutting fuel consumption by up to 50%. “We have two types of hybrid devices,” he said. FlexaGen has a Logan variable-speed motor/generator power take in (PTI) device linked to Twin Disc transmission of double-clutch design. FlexaDrive has two Logan variable-speed motor/generator PTI units on Twin Disc transmission.
“FlexaGen replaces a generator with a variable-speed electric motor, driven off the gear, that can generate electricity to the switchboard at any engine speed,” Mr Starck explained. “We are saving fuel, so there are lower emissions, and saving on wear and tear of the generators.”
FlexaGen runs all the time the engine is running, from dock to the job and then back to the dock.
“FlexaDrive has two electric motors, one on each gearbox, meaning engines can operate as generators, or a generator can operate all propulsion,” Mr Starck said.
“We selected this system because we really did not want batteries, as these are the complicated element of a hybrid system,” he commented.
Great Lakes’ tugs run long periods exclusively on the electric motors, driven by one 99-kW generator set. There are four modes of operation for these hybrid propulsion tugs. The first is the diesel electric mode for when the tug is transiting to and from the jobsite at around 5.5 knots. “While it is waiting at the jobsite, the tug can operate purely on 60-kW electric motors, which are powered by a generator,” said Mr Starck.
“At the jobsite we switch from hybrid to full diesel. But we shut down our diesel generators and use gear-driven generators, so the electric motor sends power to the main switchboard.
“After the ship assist, we switch back to hybrid mode,” he continued. “During the ship assist we also have the boost mode, where we have the generator and the main engine running, adding about 2 tonnes to our total thrust that is normally 30 tonnes.”
Great Lakes Towing has seen 73% reductions of particulate matter, 51% less NOx and 27% less CO2 from using the hybrid propulsion on these tugs.
“International regulations are driving industry towards fuel efficiency and lower emissions for all vessels, and this is important to us,” said Mr Starck. “We wanted to present ourselves as a compliant company with all the best intentions.”
That is why it decided to install a hybrid system. But there were other considerations in its system selection.
“With our hybrid propulsion, we intended to save money, so we wanted to develop the most cost-efficient system possible,” Mr Starck explained. Logan developed a system specifically sized for tug power, propulsion and bollard-pull requirements.
“The duty cycle determines the system – it is not one-size-fits-all, it is about right-sizing the system to fit your application. We operate small tugs, so we sized the system for our lower horsepower, harbour ship-assist application,” Mr Starck said.
“There are fuel savings, and wear and tear on the main engines is significantly reduced. There is more time between overhauls so there are cost savings,” he continued. “There are no batteries, making this system simple, safe and easy to install. We are in very early stages, but so far we have seen 30-50% fuel savings.”
Newbuilding tugs’ particulars
Tugs: Cleveland, Ohio, Michigan, Pennsylvania, Wisconsin
Owner/operator: Great Lakes Towing Co
Builder: Great Lakes Shipyard
Designer: Damen Shipyards
Operations: harbour towing, cargo transport, ice breaking
Length, oa: 19.5 m
Beam: 7.3 m
Hull depth: 3.3 m
Speed: 10.5 knots
Crew size: 2
Bollard pull: 30 tonnes
Engines: 2 x MTU 8V4000, 745 kW
Propellers: 3-bladed, 71-in Kaplan style in Kort nozzles
Gearbox: Twin Disc MGX-5321, with 5.46:1 ratio
Auxiliary generators: 2 x John Deere/Marathon gensets, 99 kW
Hybrid propulsion: Logan Clutch: FlexaDrive/FlexaGen
Great Lakes Towing history and operations