Report of survey: BGS 2012-9 south west approaches to Tiree multibeam and surface tow boomer survey

The purpose of the survey was to investigate the seabed directly southwest of Tiree, for the suitability of offshore installations. The total potential survey area was approximately 360km2 ; however, a priority area of interest, 232 km2 , was identified (see Figure 1). Water depths within the survey area range from 20 to 50 m. The maximum distance offshore is approximately 20 km. The initial survey specification was for full coverage by Multibeam Echosounder (MBES) with 50% overlap and Surface-Tow Boomer (STB) seismic lines to be run at 500 metre intervals. The survey commenced on the 23rd July and was completed on the 6th August 2012. The NLV Polestar was used to acquire all MBES and STB data. The focus of the survey was to complete the priority area; however, due to poor weather that limited survey time, this was not possible. Data collection in the priority area was maximized whenever possible. It was not possible to obtain 100% multibeam coverage of the priority area therefore a corridor approach was adopted towards the end of survey to ensure maximum STB and MBES coverage. During bad weather two potential cable routes were surveyed as contingency areas as both were sheltered from the predominant swell (see Figure 2 and Appendix 6). Survey operations were undertaken in all areas where navigational safety allowed. This proved difficult in certain areas of the priority area due to the presence of underwater obstructions and rock outcrops.