VESSEL REVIEW | City Tug 1 & City Tug 2 – Compact electric pusher tugs for Amsterdam’s inland waters

Dutch inland transport company City Barging has expanded its fleet with the recent acquisition of two new electric pusher tugs built by local shipyard Talsma.

Designed by naval architecture firm Van Dorresteijn, the six- by four-metre newbuilds City Tug 1 and City Tug 2 will be operated in the inland waters of the capital Amsterdam, where these will handle 60-tonne hopper barges carrying materials for various construction projects along the city's canals. A height of 1.75 metres will allow passage underneath the many bridges found throughout the capital.

"We required a vessel that was as small as possible and with electric propulsion suited for inner city transport activities," City Barging told Baird Maritime. "It was therefore built in compliance to Amsterdam's municipal requirements for vessels, which called for dimensions of no greater than 20 by 4.25 metres. Even when handling 14-metre-long hopper barges, the combined length will still fall within the maximum limitations for size."

The owner added that electric propulsion was selected for the tugs in line with Amsterdam's goal to be fully emission-free by 2025. The 230kWh battery pack is fitted into an aluminium frame with lifting points. A bolted hatch just overhead can be removed to enable the entire frame with the battery to be lifted out for replacement.

"One specific requirement was for enhanced manoeuvrability," said Fred van Dorresteijn, naval architect at Van Dorresteijn Design. "The propulsion setup therefore also includes azimuthing thrusters at the bow and the stern, giving the tugs a high turn rate. This then allows the vessel to easily push barges and get these through the tight turns in some of the city's canals."

Van Dorresteijn remarked that battery propulsion ensures all-day operation. If a higher power output is required, the tugs can be charged at midday with the aid of a double charge setup. An operator can easily switch between three different sailing modes: steering using the aft thruster only, steering using both forward and aft thrusters facing the same direction for lateral manoeuvring, and steering using both thrusters facing opposite directions to execute tighter turns.

Separate helm stations are fitted in the wheelhouse and on the aft deck on each tug. Use of the deck helm station will provide the operator with a better view over a barge being pushed when empty or carrying a minimal load.

"The challenge in designing the tugs lay mainly in finding adequate space for the installation of wheelhouse to ensure low noise and vibration levels," added van Dorresteijn. "There is a common belief that electric-powered vessels don't generate much noise, but in reality, the noise and vibration levels generated by propellers with high power demand cannot be ignored."

The designer also needed to allot space for the battery pack and the two 75kW electric motors, which came with electronic control boxes, converters, and large-diameter cables. This was due to inland vessel regulations also requiring a high level of redundancy.

"We worked with the yard in creating a full 3D setup for all components," van Dorresteijn told Baird Maritime, "and this step helped save us a lot of time. In practice, this will work only when there is a high degree of cooperation. Otherwise, the time invested in resorting to 3D will have gone to waste."

In addition to helping transport construction materials, the tugs can also handle barges carrying waste from construction sites for proper disposal.