Safety Level of a Probabilistic Admittance Policy

Abstract

The main factor restricting admission of deep-draught ships to ports is the risk of bottom contact. In the approach channels to Rotterdam and IJmuiden such ships are subject to tidal windows because of the limited depths in the approach channels. Some decades ago probabilistic methods were introduced for the allocation of tidal windows for the Euro-Maas channel to Rotterdam and later also for the IJ channel to IJmuiden. These methods are being further developed. The increased accuracy of computational methods and of forecasted wave conditions and water levels may lead to an increased accessibility of the port. Recent developments have resulted in the new tidal window advice program Protide (PRObabilistic TIdal window DEtermination). The objective of the work presented in this paper is the verification and validation of Protide for the Euro-Maas channel to Rotterdam and for the IJ channel to IJmuiden. The probability of bottom contact during channel transit is simulated for time series of ten years of measured wave data and water levels. The fleet of ships is represented by a limited number of ships and for each ship all possible tidal windows for the ten year period are determined with Protide. A database is developed with motion response characteristics for each of the representative ships. For all possible arrival times in the ten-year period, indicated as safe by Protide, a channel transit is simulated. The probability of bottom contact during the simulated transit is computed from the motion response characteristics of the ship and with the measured wave spectra and the measured water level. Two safety criteria are applied. Firstly the probability of bottom contact during a single channel transit should not be excessive. Secondly the total probability of bottom contact during a long period of application of the admittance policy should be limited. To determine the probability that a certain ship is in a certain section of the channel some elements from queuing theory are applied. The probability that the ship is present in each channel section combined with the probability of bottom contact results in the probability of bottom contact for the ship in the channel. This leads to a long term probability of bottom contact for the channel. This paper presents the analysis method and selected simulation results for Euro-Maas channel in detail.