Large tankers, bulk carriers or container vessels, where the hull girder stiff ness is relatively low compared to their size, and which need hull monitoring systems to measure the forces, motions and resulting stresses caused by the sea state. The system includes various sensors, such as long-base strain gauges, rosette gauges and trio-axial accelerometers to monitor hull girder deck stresses and localised stresses on bulkheads, side shell, cross-deck strip and double bottom structure. Real-time data from these sensors is provided for immediate use and for the evaluation of the course and/or speed changes.