## 5 Case Study: Impact of the EEDI on the Operating Performance of the FSWNS  
As the EEDI is enforced on new ships only, the existing fleet of ships will only gradually be replaced by EEDI compliant ships. This case study is carried out for scenarios where either one-third (33%) or two-thirds (66%) of arriving ships, randomly selected, have been replaced by new EEDI compliant ships. It is further assumed that the achievable speed in ice of the new EEDI compliant ships is dependent on their size in DWT as per Figure 9. Accordingly, it is assumed that EEDI compliant ships are not able to operate independently in unbroken level ice. Additionally, as per the example presented in Figure 10, it is assumed that the speed of an EEDI compliant ship, when operating in a brash ice channel or with IB assistance, might be significantly lower than that of a corresponding non-EEDI ship. In the case studies, around 30% of the replaced vessels were in the category DWT \(<\) 5100, around 60% were in the category DWT 5100-15,000, and around 10% were in the category DWT 15,000-22,000.  
Figure 8: Sensitivity of the simulation output to changes in the underlying parameter values. (**a**) ship arrivals; (**b**) instances of assistance; (**c**) mean waiting times, the results were obtained by repeating the simulation so that one category of parameters was changed at a time, keeping all other parameter values constant.  
The outcome of the simulated EEDI scenarios is presented in Figure 11. In the first scenario, in which one-third of the current fleet is replaced by EEDI-compliant ships, the number of cases of IB assistance is increased from 222 to 328 (+48%) and the total cumulated waiting times for IB assistance is increased from 775 h to 1378 h (+78%). In the second scenario, in which two-thirds of the current fleet is replaced with EEDI-compliant ships, the total number of cases of IB assistance is increased from 222 to 479 (+116%) and the total cumulated waiting times for IB assistance is increased from 775 h to 5157 h (+565%). In the second scenario, due to the extended waiting times for IB assistance, the total number of port arrivals decreases from 231 to 226 (-2%).  
Figure 10: Example comparison of the assumed speed in ice of a non-EEDI ship and an EEDI-compliant ship [26].  
Figure 9: Assumed speed in ice of Energy Efficiency Design Index (EEDI) compliant ships [26].  
Additional simulations were carried out to assess whether the increase in IB waiting time from the assumed EEDI scenarios could be mitigated by increasing the number of IBs. As per Figure 11, the outcome from the simulations indicates that in the first and second EEDI scenarios, a significant increase in the cumulated IB waiting times can be mitigated by increasing the number of IBs from 4 to 5 and from 4 to 6, respectively. Notwithstanding, due to a lack of relevant data, this assessment is based on generalizing and conservative assumptions concerning the influence of the EEDI on the ice-going capability and other technical characteristics of the merchant fleet. Thus, this case study serves mainly as an example of how the presented approach can be applied to assess the performance of the FSWNS under various operating scenarios.  
Figure 11: Influence of various EEDI scenarios on the operating performance of the Finnish–Swedish Winter Navigation System (FSWNS). (**a**) ship arrivals; (**b**) instances of assistance; (**c**) commulated waiting times, The results were obtained by repeating the simulation for the various fleet configurations considered, keeping all other parameter values constant. The cumulated port-specific waiting times reflect both the number of instances of assistance and the mean waiting time per instance