Because ships consume less fuel when operating at lower speeds, the practice of slow steaming has emerged as a cost-effective strategy during periods of reduced market demand. Recently, this approach has gained additional attention due to environmental motivations, as it offers a way to cut carbon dioxide emissions without the need for major infrastructure upgrades. Nonetheless, the downside of slow steaming is the increased voyage duration, which may necessitate deploying more vessels to maintain the same annual transport capacity. Throughout a voyage, a ship encounters varying sea conditions, which can greatly influence both fuel usage and emission levels, thereby affecting the overall effectiveness of slow steaming. As a result, evaluating the true advantages of slow steaming under realistic sailing conditions becomes essential. This study estimates the benefits of this strategy for a Post Panamax containership operating on one of the primary global container routes. Findings indicate that the time of year plays a critical role in determining the effectiveness of slow steaming. Furthermore, the variation in fuel savings along different segments of the route underscores the need for precise modeling of sea state conditions throughout the journey.