The tugboat fleet on the Great Lakes of North America is discovering hybrid drives. Consumption, environmental protection, service life and performance: The hybrid combination of an electric drive and a diesel engine offers genuine advantages, especially in working vessels. In 2019, the Great Lake Towing of Cleveland, Ohio commissioned the first three tugs with hybrid propulsion. And Rittal is also on board: as the partner for the switchgear technology of the electric drive. The decisive task for the specialist company was to build the enclosure and supply infrastructure from a standardised system and in a space-saving way. Moreover, the system had to be robust enough for maritime applications.
More powerful and more sensitive
For its new generation of tugs, the Canadian “Canal Marine & Industrial” company received an order from “Great Lakes Towing” to build an electric motor/diesel engine hybrid. The ships on the five Great Lakes between the USA and Canada can be navigated more sensitively with this combined form of propulsion. Furthermore, the electric motor handles the lower part load elegantly, while making economical use of fuel. Here, the diesel engines are under-challenged; they leave their optimum operating range and operate inefficiently. Alternatively, if more power is needed than the main engine can provide, the electric motor is used as a booster.
The system integrator has met the order from the largest shipping company for working boats and tugs flying the US flag with a Rittal enclosure solution. Canal Marine & Industrial was able to build the complex control and supply technology using standardised components from the Rittal product range. Nevertheless, the limited amount of space for the direct current supply and the inverters of the electric motors did represent a challenge. Despite all the requirements for compactness, the technology still needed to remain easily accessible. The robust design of the custom solution finally guaranteed the availability of the technology in the face of the harsh conditions faced on a working vessel. With Rittal, however, such operational reliability does not come at the expense of flexibility. The system, which is certified for maritime use, offers a modular range of enclosures, as well as flexible accessories for cable management and a host of other options for customisations or expansions.
Mastering the power losses
The details of the challenges of equipping a tugboat with an electric motor are illustrated by the microclimate prevalent in the enclosures on board. The system converts and moves power from where it is available to where it is needed by way of independently controlled and configured Variable Frequency Drives. The resulting heat losses have to be dissipated from the enclosure because rising temperatures both shorten the inverters’ service life and also reduce their performance (derating). These details have made it necessary to install an interior control system in the enclosures. The Rittal system offers fans, heating elements and a temperature control feature. Incidentally, large volumes must be transported during operation because the air in the engine room has already been heated up by the diesel engine. If the ship is moored at the quayside, the drives are at a standstill and thus not generating any waste heat. The integrated heater switches itself on during the cold season to prevent condensation from forming inside the enclosure due to the temperature drop.