Influence of bank-effect on safety of navigation of full form vessels

Bank effect, in most cases, has been analysed as hydrodynamic effect between fairway and vessel hull. This effect has been approximated with mathematical models or towing tank tests and applied in practice. Proposed models, which are verified and validated, may be used to estimate the vessel motion in the vicinity of the fairway bank. Application of the validated hydrodynamical models is most tangible trough the navigational simulators. It is important that simulator is reliable and realistic in order to assure the quality representation of realistic vessel movement. That allows us to use the simulator as a tool to estimate vessel trajectory in various conditions in order to determine the level of safety of navigation. This paper analyses the full form vessels trajectory in vicinity of the sloped banks, using navigational simulator, to determine the model for estimating the minimum distance between vessel and the bank to ensure adequate safety level of navigation. The navigational simulator is nowadays a resource which is developed to be used as teaching aid and research tool. That is possible due to reliable, proven and certified mathematical models used in simulation process. Also, real time simulator can be used for validation of mathematical model or to contribute studies in which a new navigational situation is created. In this paper validation was conducted through data comparison, between simulated data and towing tank results. These data were compared to the simulated data gathered in similar conditions. Real time simulator uses validated models to represent reliable and credible navigation condition. In this research the full form vessels are three tanker models. The tanker models were tested in fairway with sloped bank. The one of the main purposes of this research was to determine if trajectory in the vicinity of the bank, at different sailing speeds and at which distance, imposes a risk to safety of navigation. Simulated data was used to define the model, for the similar vessel types and fairway conditions. In this case multiple polynomial regression was used. This regression uses unknown parameters and their estimation using least squares method. The accuracy of the model expressed by the corrected multiple correlation coefficients is 0.9746. The recommended distances are larger for vertical wall than the sloped banks. The results show that sloped bank is, in particular cases, far more dangerous than vertical wall. The sloped bank sailing distance should be considered specifically for each situation, particularly its adverse effect in case of sailing over the bank slope. Such situations, as results showed, increase risk of grounding significantly. The influence of bank effect on safety of navigation may be significant. Vessel grounding may not be caused just by bank effect; however, its influence can be crucial. Verified bank effect model applied through navigation simulator showed that sloped banks, contrary to some recommendations, can be significant in causing vessel cross track error and consequently cause its grounding. Understanding the bank effect in sloped banks, especially when sailing over the slope, can improve the safety of navigation. Proposed model and derived distances may be used in determining the adequate level of navigation. It is necessary to take in consideration all available data and models and apply them to prevent situation which could lead to increased navigation risk levels.