# Economic Feasibility of Retrofitting an Ageing Ship to Improve the Environmental Footprint
## 2 Retrofitting the Propulsion System
### Limitations  
The installation of a power plant with LNG as fuel makes it necessary to adapt the ship's design to a specific set of needs, installing equipment and arranging spaces that would not be necessary in the case of conventional propulsion. At the same time, there are limitations related to the construction and installation of different systems on board. There is also a specific requirement for the ship's safety and people operating retrofitted equipment. Implementing power plants based on dual engines is technically complex and must comply with demanding requirements regarding their disposal on board, which are imposed by regulation. The versatility of the vessels under study greatly complicates this work since the regular operation of the new equipment cannot interfere in any way with the operations they develop. Limitations are related to a detailed analysis of each system component's location and the study of hazardous areas and escape routes per the applicable regulations. The preliminary feasibility study addressed in this section has resulted in the integration of LNG technology could become possible for the chosen vessel since it has a larger space and, therefore, offers greater possibilities in terms of generating alternatives for the integration of the necessary equipment for the consumption of LNG on board. For the installation of the LNG system, the most important fact is to find a place with enough capacity to contain the LNG tank. The selected storage tank is an independent (type C) tank. This type of tank has many possibilities of installation on board due to its portability, being only necessary for a space which fulfils the safety restrictions imposed by the IGF code [57]. Finding sufficient space for storing the gas on board the vessel is a significant factor for the success of the conversion. The LNG storage tank location can be freely selected on board the vessel and either vertical or horizontal tanks, on the open deck or below deck, can be selected. When the storage tank is above deck, the requirements set by the classification societies are slightly lower. However, in our case, it is necessary to install the storage tank above the deck because apart from the structural challenges, the difficulties in choosing the location of the gas storage tanks are also related to the bunkering possibilities at the area of selected routes. The IMO Regulations [58] were used to locate LNG storage tanks and equipment. According to them, gas storage tanks can be on an open deck or in enclosed spaces. In installing LNG tanks on an open deck, a distance of at least one-fifth of the breadth of the ship from the ship's side and open decks should be used to ensure sufficient natural ventilation and prevent the accumulation of leaking gas in the event of a leak. Tanks should also be provided with drain pans which should be fitted under the tank and should be of sufficient capacity to contain the volume that may leak out in the event of pipe connection failure. The bunkering method is essential for determining the location of the LNG tanks. Unfortunately, there is no fully developed bunkering infrastructure in the ship operation area, so only a tank on the deck is considered. As seen in Figure 1, the ship's superstructure is located as far back as possible so that it does not allow the placement of the gas storage tanks in the stern. On the other hand, the arrangement of such tanks in front of the superstructure is possible, especially since there is an engine room and spaces for auxiliary equipment below the deck, and there will be no requirement to provide space for loading and unloading operations below the main deck. The C-type gas storage tanks are most appropriate for retrofitting the structural arrangement of the multi-purpose ship analysed here. After the retrofitting, sailing on the route Varna-Poti-Varna is considered and calculated. The maximum fuel consumed for one cycle is 132 m\({}^{3}\) of LNG (with included 5% autonomy for bad weather).