Fast charging for the first all-electric tugboat in the USA

The port tug eWolf is not only the first all-electric tugboat in the Crowley fleet, but also the first of its kind in the USA. As it is powered exclusively by batteries instead of diesel engines, it can carry out its work at the Port of San Diego emission-free and almost silently. Equipped with an integrated electric propulsion system, which also includes a 6.2MWh energy storage system, the ship can be operated for an entire day on a single charge.

To make this possible, a reliable shore power infrastructure is also needed that enables a quick connection and disconnection from the charging system to recharge the ship's batteries. For eWolf, this meant developing a special connector and cable feed system that fulfils several demanding technical requirements and at the same time provides a reliable and uninterrupted power supply.

Speed is the top priority when it comes to system requirements. This is because tugboats only have a limited charging time and operators need to switch the power on and off as efficiently as possible. When such ships dock, the cable systems must supply power immediately. As soon as the charging process is complete, the system must quickly disconnect the power supply so that the tug can immediately resume its work.

Designed for a megawatt DC charging system, the conveyor system must ensure safe handling of large cables and connectors. It must also take into account the tidal amplitude of the Port of San Diego and ensure that there is always enough extra cable available to run through the tidal amplitude. However, there must be no cable loops that protrude into the working areas on the quay and interfere with the work there. To prevent this, a space-saving system is needed, equipped with special cables that can easily accommodate movement with very tight bend radii.

In order to find an optimally customised system, Crowley brought our shore power experts on board. For igus, the development for the eWolf was a unique research and development project that brought together synergies from various parties - the battery system manufacturer, the ship designers, the charging system team and the port team. igus also worked closely with safety experts who had to qualify the system for marine environments and ensure that it could withstand seismic events and storms.

The solution is a customised cable management system based on the e-dispenser shore power module. Two igus core products are included in the system: Firstly, the three-dimensionally movable triflex e-chain in the heavy-duty version TRHD.142.300.0, which is characterised by an exceptionally high breaking strength and good heat dissipation - important for cables with a high current flow. Secondly, chainflex motor cables are used in the chain. Their torsion resistance and small bend radii are ideal for the application.

The durable yet flexible chainflex cables and e-chains can withstand harsh maritime conditions, including salt water and extreme temperatures. They are also tested for more than 10 million cycles to ensure long-term reliability and efficiency. Like all igus shore power solutions, the e-dispenser is designed to fulfil all standards of IEC 80005-1, Annex D - 6.6kV, 7.5MVA and complies with the EU Machinery Directive 2006/42/EC. For a long service life in the maritime environment, it has the same corrosion protection system that is also used in the offshore industry, as well as IP67 protection for all electrical components.

A conveyor wheel with chain guide moves the e-chain backwards and forwards from the magazine via the boom. Thanks to the compact design, nothing protrudes into the quay that could hinder other work there. As the system works without sliding contacts, the tugboat is supplied with power reliably and without interruption. Pulling the cable in and out works quickly and smoothly, and it only takes about two minutes to connect and disconnect it from the eWolf.

Crowley was also pleased with the speed of the installation of the e-dispenser: igus delivered the entire system pre-assembled in a single open-top container, with the cantilever folded down for transport. On site, it only took one crane operation to lift the entire unit out of the container and position it on the foundation. The remaining assembly steps consisted only of selecting the location of the operating stations and connecting the shore power cables.