Voyage optimization for mitigating ship structural failure due to crack propagation

Abstract

Fatigue damage in ship structures starts to be accumulated from the first day when a ship is launched, while the average age of current ship fleets in different shipping segments is often older than 15 years. After many years of fatigue accumulation, fatigue cracks are widely existing in today’s ocean-crossing ships. The existence of fatigue cracks brings great challenges to ship safety, structural maintenance, associated operation cost, and so on. In order to reduce the crack propagation and enhance a ship’s structural safety during its service period, various methods could be implemented, such as decreasing cargo loadings, reducing ship speed, or even changing trade regions to be sailed in moderate sea environments. In this article, the so-called voyage optimization is proposed to plan a ship’s sailing courses with a well-designed schedule to minimize the fatigue accumulation in ship structures. Two types of optimization algorithms are used for the voyage planning, namely, the static waypoint/grid–based and dynamic waypoint/grid–based optimization systems. The capabilities of these two optimization systems are demonstrated by a 2800TEU container vessel, which was also instrumented with an old style weather routing system. One entire year of full-scale measurement data are available for the demonstration, and the crack propagation is estimated by a linear fracture mechanics–based spectral method. It is concluded that the benefits of using the proposed voyage optimization to mitigate the risk associated with a structural crack failure by more than 50%.