In this paper, the water driving cycle had been chosen to determine and compare the component sizing of conventional boat and Plug-in Hybrid Electric Recreational Boat (PHERB) powertrains. PHERB is an improvement on conventional boat to reduce the fuel consumption and emissions. The locations of water driving cycle in this research are at Pulau Kapas and Tasik Kenyir, Terengganu. Boat energy and power requirement was calculated according boat parameters, specifications and performance requirements to study the differences component sizing of conventional boat and PHERB powertrains. Power flow analyses are used to decide the size and capacity of main components for achieving the design specifications and requirements of conventional boat and PHERB powertrains. The results for PHERB powertrain requirement using steady state velocity are 20 kW at 3000 rpm for Internal Combustion Engine (ICE), 30 kW for Electric Machine (EM) and 5 kWh for Energy System Storage (ESS). The acquired results show that the PHERB gained the most existing powertrains and has extraordinary potential in applications to marine transportation in reducing fuel consumption and emission.