The application of frequency adaptive anti-roll tanks on fishing vessels is well established but currently restricted to U-tube designs. This paper concerns the initial stages of a research programme to develop a more generic anti-roll system that will be applicable to a range of tank geometries, with minimal alteration to the existing tank structure. Two possible control strategies, based on continuous and intermittent fluid flow, are assessed for a U-tube tank and the potential of extending the technique to a free-surface tank with a central partition is examined. The intermittent flow scheme was found to be most effective at longer roll periods while the continuous flow scheme was heavily reliant on a low value of fluid flow resistance.

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Significant changes of stability at sea can lead to dangerous situations and eventually stability failure. Despite its importance, the current intact stability criteria do not evaluate the motion responses of a vessel. More recently, the International Maritime Organization has identified phenomena in seaways responsible for stability failures. These phenomena can cause large roll angles and/or accelerations that can endanger ships due to critical stability situations in waves. The measurement of waves while a ship is underway is a major challenge, but ship motion is a good reflection of the wave characteristics and can be captured. Signal processing techniques are used in the detection and estimation of the influential parameters of a wave through the analysis of motion responses. Some variables of the system can be detected by spectral analysis of heave and pitch responses. These variables are the peak wave frequencies and associated magnitudes which can cause a high roll motion when similar to the roll natural frequency. The instantaneous frequency present in the signal is revealed through spectral analysis of short-time Fourier transforms in less than a minute. The instantaneous frequency is a parameter of practical importance which can be used in decision-making processes to avoid high roll motions.

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In marine design safety, decisions are based largely on the experience of the designers, expressed in a semi-formal way. Dangers are inherent in this approach, in that there is a possibility of overlooking catastrophic failure scenarios. This paper investigates a procedure dedicated to design for safety and describes its practical application to the marine design process. The developed formal safety assessment system comprises various well established safety assessment methods and statistical techniques, which in combination facilitate a novel, holistic and practical approach in incorporating safety aspects at the initial design stages. The system has been developed in the context of the Royal National Lifeboat Institution (RNLI) rescue vessel design process and was validated using various rescue vessel case studies. The formal safety assessment system and the supporting software written to facilitate its implementation are now being fully used in the development of current RNLI rescue vessel designs.