ELECTRONIC CHARTS: DEVELOPMENT OF THE MULTIPURPOSE MODEL FOR CROSS TRACK LIMIT DETERMINATION

Abstract

According to the requirements of the International Convention for the Safety of Life at Sea (SOLAS-74) vessels must be equipped with Electronic Chart Display and Information System (ECDIS). This equipment is designed to improve safety of navigation and definitely has a number of indisputable advantages over the paper charts navigation. At the same time use of ECDIS requires navigators to have a sufficient level of competency for professional operation. Inadequate setting of safety parameters as well as incorrect interpretation of information from the display can lead to an accident. The determination of cross track limit (XTL) value as one of the route safety parameters in ECDIS is considered in the paper. Some companies navigational procedures are studied; it has been found out that companies have individual requirements regarding XTL value and they can vary. The issue of XTL value determination was recently studied and the authors of the previous research had proposed their own method of XTL calculation. This method is analysed in the paper and it has been concluded that this method is applicable for determining minimum XTL value, however in order to find the optimal value it is necessary to consider ship particulars and characteristics of a specific waterway as well as company requirements for under-keel clearance. The model structure, which integrates this information, is proposed in the paper, and the previously proposed method is used within the model. The model developed by the author is flexible: the input values can be adjusted, which allows to assess the safety of any size ship passage through any waterway. The incorporation of bottom contour information into the model through a piecewise function enables to assess the under-keel clearance for any values of XTL and to determine dangerous values of cross-track distance in particular conditions. The main disadvantage of the model is a necessity to define the piecewise function which adequately corresponds with the actual depth distribution in the waterway analysed, which restricts the application of this model to natural waterways with a difficult terrain of the bottom. It should be noted that with particular input values some «borderline cases» can take place, when the safety of passage is doubtful. In order to solve these uncertainties, the model can be later upgraded by including experts’ opinions with the use of fuzzy logic methods.