## 3 Determination of Accident Scenarios and Probability
Passing ship's rudder is blocked but propulsion is operable, Polish case, (selected in this study since the propeller still produced water inflow to the rudder causing a turning effect),
3. Passing ship losing its propulsion and rudder is blocked due to extensive \"black out\", Slovenian case (similar to above but the ship is decelerating). The following are the results for the traffic analysed for the complete area presented by Figure 3 or the traffic lane calling at the Swinoujscie and the Port of Koper traffic waterways. Figure 3: Distribution of ships traffic of length more than 150 m (AIS data) for the Swinoujscie waterway-(**left**) and the entrance to Koper bay-(**right**) and in insert the cumulative distribution of rudder angle in Section 3 as a result of real time simulation study. To find the candidates for collision, the ship traffic passing through the Swinoujscie-Szczecin waterways in the vicinity of the terminal was analysed. The middle of the waterway was divided into several sections. The traffic distributions (histograms in gates No 1 to 7) from 2 years of AIS data observation (2015-2016) are presented in Figure 3. To find the PCS accident and maximum possible values of speed and impact angle due to manoeuvring characteristics of ships for the determination of further consequences, the real time simulation model described by [24] was applied, and the accident situation was simulated several times to find the worst possible values for use as parameters of consequences. In each waterway section presented in Figure 4, the real time accident simulations were performed to find the maximum angle and speed of the colliding vessel. The entire procedure was as follows:  
1. Place the ship model in starting position in three selected Sections 2-4 (in 5 different points for given section with highest probability, so 15 simulation runs were made),
2. Start the simulation,
3. Set the rudder angle to the maximum assumed for this type of ship,
4. Set engine to stop,
5. Observe and record following data: if the moored ship was struck, angle of contact, speed of contact. The above procedure could be considered as manual optimization, where the goal was to achieve the maximum angle of collision and speed during the collision. The most critical parameters for the consequences of the accident were found, and they were the angle of collision 44\({}^{\circ}\), speed 4 m/s (with engine stopped) and 2 m/s (with engine reversed). In the Slovenian case, the colliding ship had a speed of 2.9 Nm/h and angle of collision 56\({}^{\circ}\). The probability of collision in Equation (7) is further calculated where the most important factor is the hourly probability of rudder failure (\(P_{t}\)), which stands for rudder system failure. \[P=I_{w}I_{t}t_{w}t_{i}P_{t}P_{r} \tag{7}\]  
where \(I_{w}\) is the intensity of waterway traffic; \(I_{t}\) is the intensity of ships in terminal; \(t_{t}\) is the terminal occupation time \(t_{w}\) is the time of passing near moored ship; \(P_{t}\) is the probability of technical failure; and \(P_{r}\) is the probability of rudder angle position. Figure 4: Simulation model result of cruise vessel striking the moored chemical tanker at the angle of 44\({}^{\circ}\) and speed 2 m/s, after its technical failure in Poland (**left**) and the collision of the container ship into the passenger ship in Koper (**right**). This value was determined by [8] using a database of more than 77 ships of the Polish owner Polsteam over 7 years of operation. The expected value during ship passage is \(4.8\times 10^{-4}\) per hour of ships operation. For realistic traffic and input data for the police port: \(l_{w}\) = 300 ship/year, \(l_{t}\) = 40 ships/year, \(t_{t}\) = 24 h, \(t_{w}\) = 0.5 min, and \(P_{r}\) = 0.05 (starboard 30 deg. ), we obtain the probability of collision due to technical failure of the rudder estimated as \(8.9\times 10^{-6}\) yearly.