# Environmental and Economic Aspects of a Containership Engine Performance in Off-Design Conditions
## 4 Results and Discussions
### Off-Design Conditions
The annual incomes are calculated assuming the same ship sailing route for the entire year. The lowest sailing speed is determined as the speed at which the specific soot emissions significantly increase, as shown in Figure 13. For the six- and seven-cylinder engine variants, the engine can be safely operated up to a sailing speed of 15 knots, and for the eight-cylinder engine variant, up to 17 knots. With a higher number of cylinders, the NOX emissions significantly decrease, i.e., 19.7% in the case of the seven-cylinder engine variant and 34.5% in the case of the eight-cylinder engine variant. This occurred because lower engine loads in the seven- and eight-cylinder engine variants and consequently lower in-cylinder temperatures are achieved. For all engine variants and sailing speeds below the reference one, CO2 emissions can be reduced by up to 67.2%, NOX emissions up to 93.3% and soot emissions up to 53.4%. The same is true for operating costs, where the largest reduction of 27.13% can be achieved with the seven-cylinder engine variant. The largest reduction in operating costs in the case of the six-cylinder engine variant is 27.1%, and in the case of the eight-cylinder engine variant, 23.18%. The income per route slowly increases with the decrease in sailing speed. The highest feasible increase in ship income per route is 6.16% and it is achieved with the six-cylinder engine variant at a sailing speed of 15 knots. With the seven-cylinder engine variant, the highest achievable increase in income per route is 6.08%, and with the eight-cylinder engine variant, 5.06%. The annual income decreases  
Figure 16: Annual income for different engine variants and sailing speeds. with sailing speed up to 32.84% in the case of the seven-cylinder engine variant and at a sailing speed of 15 knots. The decrease in annual income in the case of the six-cylinder engine variant is up to 32.79%, and in the case of the eight-cylinder engine variant, 23.73%. The smallest decrease in annual income in the case of the eight-cylinder engine variant is because the lowest achievable sailing speed is 17 knots. Also, with the increase in sailing speed, the annual income can increase 8.58% above the reference value in the case of the eight-cylinder engine variant, but in that case, the CO\({}_{2}\) emissions would increase by 32.8%. In 2023, IMO introduced a new measure to reduce the carbon intensity of existing ships, the EEXI. It requires ships to meet certain emission targets based on their size, type, and age, at their next annual, intermediate, or renewal survey after January 1 st 2023. The aim is to achieve a 40% reduction in carbon emissions by 2030 compared to 2008 levels. The EU introduced a package of legislative proposals called Fit for 55, which also includes the reform of the EU ETS. It aims to achieve a 55% reduction in GHG emissions by 2030 compared to 1990 levels. Figure 17: Relative change in income and operating costs for different engine variants and sailing speeds for the six-cylinder engine variant. Figure 13:0 Relative change in income and operating costs for different engine variants and sailing speeds for the seven-cylinder engine variant. To comply with the regulations, in the case of the six- and seven-cylinder engine variants, the lowest sailing speed is equal to 15 knots, and for the eight-cylinder engine variant, it is equal to 17 knots, as shown in Figure 13:1  
In the case of a sailing speed of 17 knots, the eight-cylinder engine variant is the only one that complies with EU legislative requirements, but the differences are in the range of 1%. The decrease in the sailing speed to 17 knots results in an annual income decrease of around 24% compared to the reference engine variant and sailing speed. To maximize the income per route, the most suitable sailing speed is 15 knots with the six-cylinder engine variant, where the income per route increases by up to 6.2% and the CO\({}_{2}\) emissions decrease by up to 67.1%.