Data from the underway system includes observations and measurements of metocean conditions including air temperature, atmospheric pressure, relative humidity, sea temperature, salinity and wind speed/direction. Data has been collected in survey areas including the greater North Atlantic Ocean, Irish Sea, Saint Georges Channel, Celtic Sea, North Sea and Inner Seas off the West Coast of Scotland. Data has been collected since the installation of the underway system on board the RV Celtic Voyager in May 2003. Underway near-surface measurements of sea temperature are typically made using the cooling water intake of a vessel using a thermosalinograph. Underway data collection has been initiated to create a long-run time series of sea surface temperature supporting knowledge and information on the physical oceanographic conditions of waters where the RV Celtic Voyager undertakes marine surveys. Weather station data supports knowledge and information on conditions at sea during surveys. Data collection activity on-board Irelands second national marine research vessel Celtic Voyager operated by P&O Maritime Services on behalf of the Marine Institute. Data not 100% complete for every research day of vessel activity due to technical issues with underway instrumentation. Coverage estimated at >95% research days at sea.