Fatigue life improvement of weathervaning ship-shaped offshore units by a smart heading control system

This paper shows the reduction in fatigue damage, and as a consequence in the cost of maintaining hull structure that could be achieved by a smart heading control system for weathervaning ship-shaped offshore units (FPSO, FSU etc). "Smart heading control" is a proactive system which alters the heading of the unit in order to reduce fatigue damage of critical areas and therefore potentially reduce maintenance costs, downtime and risks associated with fatigue damage and or inspecting and repairing hull structure. Locations dominated by wind seas are compared with locations where swell and wind seas are often present at the same time (e.g. Norwegian continental shelf, North Western Atlantic). A Suezmax size FPSO is used to compare the “fatigue damage rate” in the connections of the secondary longitudinal stiffeners to transverse frames for locations along the length and around the girth of the hull against varying ratios of wind sea to swell sea. For seas where the ratio of wind sea energy to swell energy is close to or less than unity and where the swell and wind seas are from different directions the SHC system reduces the fatigue damage by a factor of three. •SHC "Smart heading control" is a proactive system altering the heading of a ship shape offshore unit to reduce fatigue damage.•An FPSO is used to compare the fatigue damage rate with SHC system versus free weathervaning condition in the connections.•SHC can third the fatigue damage for seas with dominant swell component where swell and wind seas have different directions.•For seas with highly dominant wind sea component, SHC would be less beneficial and unlikely to be cost effective.•SHC should be switched off during offloading and shuttle tanker mooring for operational and/or safety reasons.