Electric tugs bring environmental and opex benefits
Crowley has ordered the first all-electric tug in the Americas and Navtek provides data from two years of operating Gisas Power
Tug operators are increasingly investing in new tugs with low or zero-emissions propulsion. The transition is being driven by upcoming green legislation, public opinion, and the ability of batteries to power harbour vessels. An expert panel during Riviera Maritime Media’s Tug transitions to zero emissions webinar provided their unique experience of designing and purchasing the industry’s first electric-powered harbour tugs.
This event, sponsored by Navtek Naval Technologies, was held 16 March 2022 during Riviera’s International Tug & Salvage Webinar Week, in association with premier partner Uzmar. During the webinar, Crowley Shipping vice president Paul Manzi explained why Crowley invested in the first fully electric-powered harbour tug to be operated in Americas.
Crowley ordered 25-m tug e-Wolf from Master Boat Builders’ shipyard in Coden, Alabama to begin operating in the Port of San Diego in California mid-2023.
Corvus Energy is supplying the energy storage system (ESS) for e-Wolf. At 6.2 MWh, this battery system is the largest ESS so far ordered for any tugboat. ABB will integrate the ESS with the rest of the electric propulsion and Schottel will supply two RudderPropellers of type SRP 430, embedded L-drives and the MariHub data gateway and monitoring solution.
“We are on the cutting edge of engineering with the design and use of electric tugs in Jones Act trade,” said Mr Manzi. “This electric tug will reduce our Scope 1 direct emissions and enable testing of the engineering we could then apply to the rest of the fleet.” Scope 1 emissions makes up around 80% of Crowley’s total emissions, the rest being Scope 2 indirect emissions.
Crowley operates around 160 vessels in sectors including ports and logistics and aims to become the most sustainable and innovative maritime and logistics company in America.
e-Wolf was designed by Crowley Engineering Services and will be funded by federal and state grants, as will the associated charging station in San Diego.
e-Wolf is a transformational vessel that will chart a new course for the industry. We expect e-Wolf to operate with zero emissions. It will have a diesel generator on board only for emergency purposes.Paul Manzi.
He expects considerable savings in carbon, NOx and SOx emissions.
e-Wolf is also designed to operate autonomously, with Crowley maintaining real-time visibility of operations. This is just the beginning, as Crowley has designed another electric-powered tug it plans to operate in Los Angeles and Long Beach ports.
Mr Manzi said this will have two designated battery rooms, generators for long transits, L-drive electric thrusters and air-conditioned machinery spaces.
Crowley’s tugs have self-rescue capabilities “for easy rescue if someone falls overboard” and several advantages.
There are no exhaust stacks, which gives masters 360° of visibility from the pilot’s station. They are capable of fully autonomous operations, to increase the safety and efficiency of the operation.”Paul Manzi
This latest tug naval architecture and e-Wolf were designed to ABS class and are compliant with US Coast Guard sub-chapter M regulations.
“The modular batteries can be replaced as they age,” said Mr Manzi. “Battery operational efficiency is really important.” Crowley will monitor battery performance, charge and output remotely.
The shore power station and supply management are also innovative. “We are developing end-to-end shore power,” he said. The station will be charged from the existing grid at 12 kV and will charge e-Wolf at a rate of 1 MW/hr. The battery packs are to be housed in containers.
Solar panels will be installed on the roof of the containerised charging station to provide additional power to e-Wolf’s electrical systems during onboard battery charging.
All this comes at an additional cost to diesel-driven equivalent tugs. Mr Manzi said capital expenditure of e-Wolf is 40-50% higher than conventional tugs. For comparison, a tug with hybrid propulsion is 30% more expensive to construct than a diesel-driven tug.
But the environmental benefits for tug owners and ports are high.
“Entry into the zero-emissions tug world is opening a great deal of opportunities for ports for where they can zero-out their emissions,” said Mr Manzi.
Electric tug experience
Navtek Naval Technologies general manager Ferhat Acuner explained some of these benefits from experience running electric-powered Gisas Power in Turkey for two years. This ZeeTug 30 design vessel was brought into service March 2020 and completed its first annual survey March 2021. Data within Mr Acuner’s presentation was from a report into its performance after 583 days of operation.
Actual operating days were 552, and in that time, Gisas Power completed 1,532 operations. Motor running time was 1,930 hours, and it was off for maintenance for 75 hours, which is less than 4% of total hours.
Charging during the 583 operating days was 380,000 kWh. Mr Acuner said this was important because it is the first set of statistics on operations and charging.
Gisas Power completed 2.8 sorties per day on average and operational days were 95.0% of calendar days. The state of health of its lithium-ion batteries was 99.5%, average discharge rate was 0.55 and average charge rate was 0.65.
Mr Acuner said the operating expenditure savings from reduced fuel costs (versus an equivalent tug on marine diesel) was 50% and total maintenance and repair cost savings were 21% due to less mechanical equipment to maintain.
Gisas Power has saved 318 tonnes of CO2 emissions, equivalent of 210 tonnes per year, and saved 0.83 tonnes of NOx emissions.
“In the future, tugs will be less polluting and less noisy than diesel-powered tugs,” said Mr Acuner.
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