The shipping industry is seeking various technological solutions to reduce carbon emissions, and ammonia (NH3) is gaining attention as a next-generation zero-carbon fuel. Ammonia has the advantage of not emitting carbon dioxide (CO2) and can be transported and stored on a large scale using existing infrastructure. This study evaluated the performance of a hybrid electric propulsion system that supplies hydrogen (H2) generated from the reforming of ammonia to a fuel cell to produe electricity. The system, consisting of ammonia-hydrogen reformer, a hydrogen fuel cell, and a battery, offeres an eco-friendly propulsion method. A heel test was conducted to assess the stability of the system under a 10-degree inclination, a condition that vessels may experience during actual navigation The test results indicated that the ammonia reformer consistently produced hydrogen even under inclined conditions. The hybrid system, which combines the fuel cell and battery, effectively managed power and maintained a stable electricity supply even with load fluctuations. Notably, it was confirmed that the interaction between the fuel cell and battery occurred smoothly without performance degradation of the system, even in an inclined state. This study is significant in that it experimentally verifies the stability and performance of an ammonia-based propulsion system, which has the potential to become a key technology for eco-friendly vessels in the future. Therefore, the results of this study are expected to provide important foundational data that will enhance the commercialization potential of ammonia-based propulsion systems in the shipping industry.