Around two years ago GİSAŞ approached NAVTEK, the Istanbul-based ship designer and builder with a challenging request. They wanted to replace their existing fleet of harbor tugs with vessels that were both smaller and with lower emissions to meet increasingly stringent port regulations. At first it seemed that these demands might be incompatible, despite an increasing utilization of hybrid diesel-battery configurations and some clean-tech add-ons.
The NAVTEK’s solution was to design a full electric tugboat. Executing the project, required some inspired engineering. With a length of just 18.7 meters and a 6.7 meters beam (maximum width), the main challenge was the sheer scale of the electrical power required to enable the tug to deliver the minimum 30 tons bollard pull.
In addition to the challenge of meeting the required bollard pull, conventional variable speed drive (VSD) technology would have taken up more space than was available on the tug.
Mobile drive enables a small installation footprint
To overcome this challenge, BMA Technologies, a marine electrical system integrator, approached ABB for technical support. The compact ABB HES880 Mobile Drive, a crossover from heavy-duty industrial applications such as the mining industry, was found to be suitable. In particular, a number of the liquid-cooled drives could fit within the tug’s limited footprint as they do not need to be mounted in cabinets, while providing the power needed for the 925 kilowatt (kW) propulsion motors. With its high vibration tolerance (4 g continuous and 30 g shock) and IP67 rating, the drive offers the rugged, reliable performance demanded by arduous and hostile marine environments. The first Zeetug30 was constructed at Istanbul’s TK Tuzla Shipyard. Altogether, ABB supplied 14 HES880 Mobile Drives. This includes six battery DC/DC converters, two inverters for each of the propulsion motors, one each for the propulsion and fire-fighting (FI-FI) pump, and two 150 kVA off-grid converters for the tug’s hotel load.
Powerful, yet energy-efficient
Compared to similar-sized, diesel-mechanical tugs, the all-electric Zeetug30 is expected to save 210 tonnes in carbon dioxide (CO2) emissions and 9 tonnes of nitrogen oxides (NOx) emissions per year. A further advantage, demonstrated during the testing and commissioning phase, is that the all-electric design needs less energy to complete its operations than calculated originally.
The tug’s operational costs are equally impressive. The estimates are that, when the Zeetug is in full service, it will cost up to 85 percent less to operate than a diesel-engine tug of similar size. In addition to improved energy-efficiency, other benefits of the all-electric design are the reduction in the maintenance time and costs associated with diesel engines. Furthermore, remote monitoring and diagnostics allow technicians and engineers to resolve any issues in real-time, while any software system updates can be performed remotely. During the test program, Zeetug30 exceeded the target bollard pull of 30 tons with a maximum pull of 32 tons.
Maneuverable and easy to operate
Zeetug30 is currently operating daily in the shipyard section in the Port of Istanbul, where space is severely restricted. After months of operation, the crew members have expressed their overall satisfaction with the tug, listing its maneuverability, fast response to commands, and instant propulsion power as its most impressive features. The fully-electric propulsion system allows the tug to turn in very tight circles, making it a much safer option in emergency situations or wherever fast reaction time is needed.
The Zeetug30 will perform harbor duties during the day and will be recharged overnight via a shore-side connection. The tug’s batteries can be charged within an hour, which can be reduced to half an hour depending on shore-power capacity and location.
An electric future
Customers worldwide have already expressed significant interest in the Zeetug30 and NAVTEK’s business development department is working on several quotations. Because of the nature of battery-powered technology, energy profiling and consumption are important, and customers may have different operational requirements, so the design will be adapted accordingly. Zeetug30 is set to haul port operations into a zero-emissions future.