# Environmental and Economic Aspects of a Containership Engine Performance in Off-Design Conditions
## 4 Results and Discussions
### Off-Design Conditions
The ship is designed to carry 6750 TEU, which is equal to 3375 FEU and represents a cargo value of USD 8,707,500.00. The reference ship marine engine is the six-cylinder engine variant. As each new cylinder section of the Wartsila Sulzer RTA-96C engine series adds additional weight, the seven-cylinder engine variant has 130 tons more weight [37], which is the weight of 5 TEU and the carrying capacity for the seven-cylinder engine variant is 6745 TEU. The eight-cylinder engine variant has 300 tons more than the six-cylinder engine variant, which means that the carrying capacity of the eight-cylinder engine variant is 6738 TEU. That represents a decrease in cargo value of 0.07% and 0.18% for the ship configuration with the seven-cylinder and eight-cylinder engine variants, respectively. In general, the operating costs are comprise fuel costs, port charges, crew costs, repair and maintenance costs, insurance charges, parts and lubes costs, and administration costs [38]. According to the diagram which depicts the distribution of operating costs of Panamax, Post Panamax and Post Panamax plus containerships sourced from Drewry Shipping Consultants Ltd., London, United Kingdom in [38], in the case of a Post Panamax containership, the fuel  
Figure 13: The comparison of soot emissions for engine variants at different sailing speeds. contributes to 49% of operating costs, port charges to 23%, insurance charges to 8%, repair and maintenance costs to 8%, stores and lubes to 2%, manning or crew costs to 8%, and administration to 2%. The fuel costs and overall operating costs were calculated based on the global 20 ports' average price of Very Low Sulfur Fuel Oil (VLSFO), also known as IMO2020 grade bunkers, which is currently 658 USD/ton [39]. The operating costs for all engine configurations are calculated based on the assumption that 49% of operating costs are fuel costs and all other operating costs are calculated according to their above-mentioned contribution to overall operating costs. The reference operating costs are calculated for the sailing speed of 23 knots at which the ship can sail the selected route in 195.5 h. Insurance charges, repair and maintenance costs, stores and lubes costs and administrative costs are assumed independent on sailing time and frequency and these costs are set to constant values. Crew costs are calculated by multiplying the required sailing time and the crew costs per hour. Figure 14: Operating costs for different engine variants and sailing speeds. Figure 15: Income per route for different engine variants and sailing speeds. The crew cost per hour (825.3 USD/hour) is calculated by dividing the reference crew cost (161,363.75 USD/route) by the reference sailing time (195.5 h). The operating costs decrease with the reduction in sailing speed, as can be seen in Figure 14. The reduction in operating costs is the result of lower fuel consumption in the analyzed operating range of the engine. At the reference sailing speed (23 knots), the six-cylinder engine variant has the highest operating costs (USD 1,457,491.47) because the highest fuel consumption is reached. On the other hand, the eight-cylinder engine variant works at the most efficient engine operating point, resulting in the lowest operating costs (USD 1,453,675.24). The operating costs decrease with the increase in the number of cylinders at sailing speeds of 19, 21, and 23 knots. At lower sailing speeds, the differences between the operating costs for different engine variants are negligible. The decrease in operating costs results in an increase in ship income per route, as shown in Figure 15. Due to longer sailing time, less cargo can be transported in one year and therefore the annual income decreases significantly with the reduction in sailing speed, as shown in Figure 16.  
Relative changes in emissions, operating costs, income per route and annual incomes with sailing speed for all three engine variants compared to the six-cylinder engine variant at the design speed of 23 knots are shown in Figures 17-19.