This article proposes an analytical model for a conversion from Heavy Fuel Oil (HFO) to Liquide Natural Gas(LNG) dual-fuel engine in a fleet with three sizes of vessels in order to investigate the impact of the volatility of oil prices, and a declining Energy Return on Investment (EROI) on opting LNG as a reliable marine fuel. This study also attempts to echo the importance of looking through a new window to the process of energy opting in the maritime industries to comply with International Maritime Organization (IMO) regulations. With giving this awareness to the maritime society the new investment can be directed to resources that effectively keep the maritime economy growing and can also help build a sustainable future. In order to find the best answer, we need to seek alternative solutions that will sustain shipping’s competitive edge. In the first phase, the impact of a declining EROI gas is investigated. Then, in the second phase, to be able to find an optimal area to run the vessels, we apply the Computerized Engine Application System (CEAS) in order to predict the engine performance of different container vessels and outlined fuel consumption in various market and technical situations. Since the process found is a non-linear system, this paper attempts to investigate the ongoing trend of the EROI of LNG in applying a Net Present Value (NPV) as a simulation method in order to observe the system to which technical variables or legal frameworks is more sensitive. In the following order, we first characterise the uncertainty faced by policy-makers and complexity dynamics implications for investment decision-makers and technology adoption. The practical relevance here of the proposed applied methodology is subsequently discussed in reference to four scenarios relating to the above areas and introduces the most beneficial area between different vital variables and constraints. It is applicable for the management of cascading uncertainties and the cross-sectoral impact by introducing the most beneficial area between various vital variables and constraints; including LNG prices, Capital Expenditure (Capex), Operating Expenditure(Opex) and time of enforcement.