This dataset contains the Underway (UWY) data collected on commercial ferries plying the Rottnest to mainland route. Voyages take place on a commercial schedule. A Seabird SBE38 sensor is permanently mounted on the ferry in the engine cooling waster intake. A monitoring computer records sea surface temperature whenever the vessel achieves more than a minimum preprogrammed speed over ground. Position is determined from a GPS unit. Data is transmitted to CSIRO Marine and Atmospheric Research centre in Hobart on the hour every hour. The vessel traverses the route from Hillarys Boat harbour to Rottnest 3 or four times per day except during a winter vessel maintenance period. This dataset has been processed and is archived within the CSIRO Marine and Atmospheric Research Data Centre in Floreat.