6 OCTOBER 2017 • FOGHORN FOGHORNFOCUS: MARINE PROPULSION O perational costs, en- vironmental-friendly solutions, and EPA regulations are all important factors in the future of ferry propulsion. Double-ended ferries carrying passengers and vehicles across sounds are a vital link in the Pacific Northwest transportation network. For many of these routes, pure battery ferries are already a realistic choice, charged with shore connections from the grid. Shorter near-coastal ferry routes are ideal for all-electric propul- sion systems as they have a predictable operational pattern and a limited power demand per crossing. In the past few years, a transition towards all-electric ferries have started in Norway, where operational requirements are similar to the Pacific Northwest. In Norway, regulations and funding have been drivers in the all-electric ferry development. Several Norwegian operators are making the investment and all- electric ferries have become a reality, the first one already having more than two years of operational experience. Rolls- Royce Marine has developed SAVeCHARGE, an all-electric propulsion-system for these ferries, utilizing its extensive background in hybrid and diesel-electric installations. New Technology: Batteries have seen a great develop- ment in the last years and frequency converters are getting more and more reliable. In a simplified electric propul- sion system the three main components are the batteries, frequency converters, and electric motors connected to the propellers or thrusters. To explain how they work, a com- parison to a hydro power plant can be made. The batteries do the same as the dam; they store energy and have it ready for whenever you want more power. The frequency convert- ers are comparable to the main valve in the hydro plant. The valve opens or closes gradually to adjust the amount of water that is taken from the dam and then turned into power. The frequency converter controls the amount of electric power that is pulled out of the batteries and put into the electric motor. The next step in your power plant is the generator that transforms the amount of water coming through the valve into the desired electric power. On the propulsion All-Electric – The Future of Ferry Propulsion By Kristian Eikeland Holmefjord, Rolls Royce Marine Engines system, the electric motor transforms the amount of electric power coming from the frequency converter into a rotating movement to the propulsor, creating the thrust needed to move your vessel. The control mechanism is a critical part for both systems; the generator will transform waterpower to electric power controlled by the valve, while the electric motor will transform electric power to waterpower con- trolled by the frequency converter. System: Integration of all components in the system can be a challenge. In most cases the supply of electric motors, propeller units, frequency converters, energy storage, and control system are supplied from separate entities. The SAVeCHARGE system illustrated in the figure above is a unique offer from Rolls-Royce where the thrusters, frequency converters and control system are manufactured and inte- grated by one entity. Small backup generators can be installed for system uptime in instances where a power outage is present on the landside grid. A complete system reduces both installation time and commissioning time compared to a split delivered system. The system is optimized towards energy efficiency by minimizing the amount of energy con- versions needed and utilizing permanent magnet motor technology for high efficiencies at all power levels. This will reduce the operational cost of energy and reduce capital cost since smaller battery installations can be used for the same crossing distances. Rolls-Royce recently signed several contracts to supply its first automatic crossing system to new double-ended battery and hybrid ferries in Norway. Such an automatic crossing system ensures safe and energy- efficient transit back and forth by automatically controlling the vessel’s acceleration, deceleration, speed and track. These systems ensure consistent behavior during the journey and hence predictable energy consumption as well as optimal loading for the different components in the system. Safety: Lithium-ion battery technology is in most cases the best technology for a near-coastal ferry. It gives a high A simple charging system, in this case the Rolls- Royce SAVeCHARGE system, can drive a short-run ferry exclusively on battery power.Artwork courtesy of Rolls-Royce. Editor’s Note: This article was originally published in Pacific Maritime Magazine, March-edition 2017. The article has been updated by the author to reflect the newest development in all- electric ferries.