This marine geophysical and multibeam survey was undertaken in July/August 2012 off south-west Tiree by the British Geological Survey (BGS) on behalf of Marine Scotland on board the Northern Lighthouse Board vessel NLV Polestar. Sea floor bathymetry data were collected using a Kongsberg EM3002D multibeam system. Sub bottom seismic profiling data were collected using a surface tow boomer. The data are archived by BGS and are also available on Marine Scotland Interactive (MSI) - http://www.gov.scot/Topics/marine/science/MSInteractive/Themes/Renewables/Data. Multibeam bathymetry data are available from the UKHO Bathy DAC, https://www.gov.uk/guidance/inspire-portal-and-medin-bathymetry-data-archive-centre. Backscatter data are available from the backscatter layers in the BGS Offshore GeoIndex. Technical details of the survey are contained in BGS Report of Survey CR/12/099, https://nora.nerc.ac.uk/id/eprint/529501/. GeoIndex Offshore - https://mapapps2.bgs.ac.uk/geoindex_offshore/home.html?cruise=2012/9_MS&;.