This record describes multibeam echosounder data collected on RV Investigator voyage IN2021_V03, titled "Integrated Marine Observing System: monitoring of East Australian Current property transports at 27 degrees South (multi-year)." The voyage took place from Hobart (TAS) to Brisbane (QLD) between May 8 and June 3, 2021. The Kongsberg EM710 MKII multibeam echosounder was used to acquire seafloor bathymetry and backscatter information and watercolumn backscatter between Hobart and Brisbane. The EM710 MKII provides a 0.5° by 1° transmit and receive angular resolution respectively. The echosounder's nominal frequency range is from 40 to 100 kHz. Data are stored in *.all raw format for bathymetry and backscatter and *.wcd format for watercolumn backscatter at CSIRO. There are 317 files totalling 41.9 GB of raw data in this dataset. Sound velocity profiles were applied to this data during data acquisition. Bathymetry data contained in *.all format are corrected for motion and position. The data has been reduced to approximate Mean Sea Level (MSL) using the Earth Gravitation Model 2008 (EGM2008) 1 arc-minute x 1 arc-minute grid spacing. GPS corrections were not applied to the processed data. Processed data has had outliers removed. Processed line data are available in *.gsf and ascii format, and processed bathymetry and backscatter grids in geotiff format. Additional information regarding this dataset, including further information on processing streams, is contained in the GSM data acquisition and processing report. Additional data products may be available on request.