Fatigue and Hull Life Span

All vessels are built with a given fatigue capacity when leaving the shipyard. This fatigue capacity is being reduced from the very first day in operation. Theoretically, this fatigue capacity reduction is evenly distributed over the projected life span of the vessel. Maintenance schedules and procedures are based on a gradual reduction of fatigue capacity. Actual events however might not mirror theory. Peak stress loads during loading, discharging or heavy weather might accelerate the development of fatigue in the hull. SENSFIB provides the possibility to monitor hull fatigue development closely and adjust maintenance schedules accordingly. If fatigue progress is more rapid than planned, corrective maintenance, such as repair of local cracks and coating damage might be necessary. The reverse might also be true if fatigue progress is slower than planned. Unnecessary scheduled maintenance can be avoided and maintenance cost can be reduced.

Hull fatigue is a function of dynamic hull stress amplitude and the number of load cycles. The economic impact for the ship owner of this simple relation is illustrated in the diagram below. Average dynamic stress levels of 12% of the instant failure level will result in a hull life span of 23 years. An increase of average dynamic stress levels to 18% will reduce hull life span to just 8.6 years before fatigue.

Onboard preventative measures to reduce dynamic stress levels greatly inpact the life expectancy of the vessel. SENSFIB monitors hull stress levels and can help the crew to keep dynamic stress level within safe operation levels. SENSFIB data can be relayed on-shore for analysis by the operator's operations department. Maintenance schedules can be optimized using the hull fatigue data from the vessel. Cargo operations and ballasting procedures can be altered to reduce hull stress load.