Effective energy density in small vessels: a comparative study of diesel engines and battery electric propulsion systems

The electric propulsion system has recently attracted considerable interest due to its advantages in reducing emissions. Nevertheless, the deployment of electric propulsion systems in small vessels necessitates rigorous examination and validation. Rather than adopting electric propulsion systems without due consideration, it is preferable to conduct a comprehensive evaluation of their feasibility at the design stage. This study proposes an evaluation method for propulsion systems suitable for small vessels based on effective energy density. The objective is to consider propulsion system equipment factors from the design stage and assess their applicability to small vessels. A reverse design of a battery electric propulsion system for a GT 9.77 fishing boat was conducted, and its effective energy density was compared with that of the original diesel engine propulsion system. The findings demonstrate that under identical weekly sailing design requirements, the effective gravimetric energy density and effective volumetric energy density of the diesel engine propulsion system are 11.95 times and 13.14 times greater, respectively, than those of the battery electric propulsion system. This finding indicates that, given the limitations of current battery technology, battery electric propulsion systems are not a viable option for long-duration sailing fishing boats. Further analysis indicates that the effective energy density of the battery electric propulsion system is superior to that of the diesel engine propulsion system under low-speed, short-duration operating conditions. The findings of this study indicate that the evaluation method based on effective energy density at the design stage is an effective means of determining the suitability of a chosen propulsion system for specific application needs of small vessels. This approach facilitates the design and selection of appropriate propulsion systems.