6 th OSAKA Colloquium on Seakeeping and Stability of Ships Osaka University, Japan, March 26-28, 2008 RISK-BASED ONBOARD GUIDANCE TO THE MASTER FOR AVOIDING DANGEROUS SEAWAYS Dimitris SPANOS, Apostolos PAPANIKOLAOU and George PAPATZANAKIS Ship Design Laboratory, National Technical University of Athens, GREECE ABSTRACT The concept of a ship specific Decision Support System (DSS) for onboard navigational guidance to mitigate the risk related to the seakeeping performance of ships is introduced. The developed approach utilizes data related to the prevailing operational, loading and environmental conditions, which can be random and uncertain, as well as to the theoretical hydrodynamic responses of the ship in order to evaluate the related risk and explore for possible lower risk options. The involved probabilistic analysis is conducted by use of numerical simulation/sampling methods, like Monte Carlo simulation as well as FORM/SORM probabilistic assessment methods known from their application so far to ship’s structural reliability analysis. The proposed risk-based DSS concept proved feasible for onboard/online navigational guidance to the master, disposing practical computational efficiency for the demanding onboard risk evaluation problem. KEY WORDS: Risk, decision, uncertainty, seakeeping, hazard, probability, limit states, FORM, SORM INTRODUCTION The prediction of the seakeeping behavior of ships for a variety of probable environmental, ship loading and operational conditions can be nowadays considered satisfactorily addressed by various deterministic hydrodynamic and probabilistic assessment methods, providing important information about the design and efficient/safe operation of modern ships. The above problem is however still a challenge when considering onboard applications in relation to the support of navigational decisions by the master in severe seaways, despite some progress even at IMO regulatory/advisory level, IMO (1995, 2007), Papanikolaou et al. (2000). In the deterministic seakeeping analysis, calculations are based on assumed ship inherent and environment dependent data. However, in realistic conditions each parameter of the seakeeping problem, even sensitive to seakeeping ship characteristic input data, like GM and radius of roll gyration, are bound with a degree of uncertainty, whereas other parameters, like environmental data, are inherently random. Above random variables and uncertain parameters define an intricate probabilistic assessment problem, the satisfactory solution of which is quite complex and computationally very time demanding for onboard/online applications. In this paper the concept of a ship specific, risk-based onboard Decision Support System (DSS) for mitigation of the risk related to ship’s seakeeping behavior in severe seaways is introduced. The concept is determined by the risk-based decision which it supports and the employed risk evaluation method. The risk evaluation and particularly the related probabilistic assessment is the heavy computational part of the full system; it has been adjusted to allow the use of probabilistic methods known from the structural reliability theory to efficiently deal with all kind of related randomness and uncertainties. The presently outlined DSS has been successfully implemented (Papatzanakis, 2007) by use of a typical seakeeping prediction code, (NEWDRIFT, (Papanikolaou, 1989)) and a probability analysis software (PROBAN, (DNV, 2002)). The current implementation has been employed to analyze a representative set of hazards related to the behavior of a ship in waves and to investigate the feasibility for onboard applications with respect to the computational performance and accuracy. The development of the DSS concept has been conducted within the research project ADOPT (2005-2008), which addresses the feasibility of such systems for practical implementations. The herein presented concept is one of two basic concepts identified and investigated in this project. While both of them follow a common basic functionality, they are different in the way the ship motion analysis is conducted (namely in frequency or time domain), the employed probabilistic assessment methods and the risk mitigation approach. A detailed description of both concepts is due to be presented in another forthcoming conference COMPIT (2008). THE DSS CONCEPT The herein risk-based Decision Support System (DSS) aims at the mitigation of risks arising from the intact ship motion in waves. Hazardous events related to seakeeping behavior are identified and formulated. Then the probability of those events is numerically estimated exploiting information available onboard. Given these probabilities and assuming corresponding consequences (which may be economic or safety related) the risk evaluation follows. Alternative sailing conditions of lower risk are explored by the DSS.