b'FOGHORN FOCUSNext Steps in ELECTRIC PROPULSIONPART ONEJUDY CUSHMAN DuBOSE, ADAM JOST AND ED BORGEAUTHRUSTMASTER OF TEXASM ostpeoplethinkofthrustersasanused in normal operation.As a consequence theanddisembarked. Thistimeperiodcanbe auxiliarypieceofmachinery,likeferryboat operation will not emit greenhouseusedtotransferenergyfromshoretothe abowtunnelthruster.However,gases and the energy used for the ferryboat willvessel. Additionally,theenergyusedbythe they go far beyond this as explained in thiscomefromanefficientelectrical-generatingvessel while it is managing ferry traffic can be article. They include lines of tunnel thrusters,source provided by the shore-based utility.providedbytheshorepowersystemwhile azimuth thrusters, retractable thrusters, withsimultaneously charging the vessel batteries.some companies extending their off erings toThebarriertothislowemission,lownoise complete electric propulsion systems as well.strategy is the storage of energy on the vessel.Rapidlychargingthevesselbatteriesfrom PVA member Thrustmaster of Texas is one ofThe battery technology available today cannotthe existing shore power utility could incur the companies leading the way with this typemimictheenergystorageprovidedbylargesignifi cantcostsinthattheinfrastructure of system and shares specifi cs about it below.diesel fuel tanks.The battery technology canwouldhavetobesetuptoaccommodate store enough energy to operate the ferry for aasignifi cantpowerfl Thecommercialow.The electrical system that is detailed here islimited number of roundtrip crossings.Thearrangementswiththeshore-basedutility anall-electricsystemwhichallowstheferryrestricting factor is moving the energy fromaresuchthatdemandingapeakpowerfor to transit back and forth between terminalstheshoreontothevesselwithoutdelayingshort time incurs a penalty on costs on the and islands using energy stored in propulsionthevesselsschedule. Whentheferryboatremainingpowertransferregardlessofits batteries. The design intent is that the dieselis not traveling on route, it is brought intomagnitude.The intention of this is to avoid generator set that is on the vessel would not beadockwheretheferrytrafficisembarkedexposingtheutilitytoshort-termexcessive demands. Asnotedearlier,theefficiencies gained by using a shore-based utility are due largely to the fact that the utility operates large generators running at a steady load.If peak demands appear on the grid, they must be met bytheapplicationofadditionalgenerators that are on line for a short time.This drives upthecostoftheenergyproducedandas aconsequencetheutilityincreasesthecost for power to consumers that have such peak demands.In addition to this, peak demands on the utility are met with power that is not produced as efficiently as steady state power and this could in turn increase the emissions of the shore based power generation system.Theshoreelectricalsystemfacilitywould accumulate energy steadily from the utility over the period of time that the vessel is traversing the crossing.Since the total energy necessary to charge the vessel would be transferred from the grid over a longer period of time, the peak FOGHORN FOCUS: MARINE PROPULSION 12 FOGHORN'