Maritime transportation is an essential part of the global transportation network and facilitates a significant share of commercial and economic activities (Fratila et al., 2021). Over 90% of global trade in terms of quantity and over 70% in terms of value is carried out through maritime transportation channels (Scarbrough Ricardo et al., 2022). Compared with air and land transport, shipping is a more economically viable and environmentally friendly option. Nevertheless, the fossil fuel propulsion systems often employed in maritime transport encounter a range of critical issues. The foremost concern is their significant contribution to marine pollution by releasing pollutants such as sulfur dioxide, nitrogen oxides, and particulate matter into the air and water. These emissions not only degrade the air quality along coastlines but also harm marine ecosystems (Andersson et al., 2016). Moreover, carbon dioxide emitted by these systems accelerates ocean acidification and drives climate change, resulting in rising sea levels and unpredictable weather patterns that pose substantial challenges to maritime operations and coastal communities. According to the International Energy Agency (IEA), after a sharp decline in 2020, emissions from the global shipping industry will increase by 5% by 2021, surpassing 2015 levels (UNCTAD, 2022). Reliance on finite fossil fuel reserves further exposes the maritime industry to supply chain vulnerabilities and price fluctuations. To overcome these issues, the transition toward cleaner alternatives, such as advanced propulsion technologies and sustainable energy sources, has been at the core of research.

Electrical propulsion systems are promising for sustainable maritime transportation. Renowned for zero emissions at the point of use and reduced noise levels, electric motors offer compelling environmental benefits. Moreover, their inherent efficiency and precise control over thrust and speed contribute to enhanced performance, maneuverability, and operational advantages. The flexibility of being powered by diverse energy sources, including renewables, further positions electric propulsion as a key player in decarbonizing maritime transport. Electrical propulsion systems are characterized by their flexible arrangement, which reduces the space requirements for the engine room. As a result, it is possible to increase the deadweight while simultaneously reducing the levels of vibration and noise, as well as the associated maintenance expenses (Kim et al., 2007). Electric propulsion systems offer significant advantages in terms of enhancing efficiency and ship design compared to conventional propulsion systems, including improved prime mover efficiency, improved propulsor efficiency, reduced radiated noise and vibration, and enhanced reliability and survivability (Nuchturee et al., 2020). Although electrical propulsion offers multiple benefits, it presents several significant challenges. An example is the low power density of the utilized batteries compared to other energy storage devices, such as supercapacitors (Yasin et al., 2024), which impacts the operational feasibility. Moreover, battery degradation over time requires costly replacements and raises concerns related to the ecological impact on the end-of-life of the battery. Environmental considerations span the resource demands of battery production and their disposal (Ammar and Seddiek, 2021).

Hybrid propulsion systems have been proposed to overcome these shortcomings. These systems combine conventional fuel-based propulsion with renewable energy sources to reduce expenses and emissions and improve overall performance. Diesel-electric propulsion has the potential to be flexible and efficient. Using electric motors to power a ship’s propellers simplifies the adjustment of the ship’s speed and direction and allows the system to be fine-tuned for optimal efficiency considering the vessel’s operational parameters (Zaccone et al., 2021). Some hybrid propulsion systems utilize this approach to enhance efficiency and reduce emissions by integrating it with other technologies, such as wind, solar, or battery power (Dedes et al., 2016), (Nüesch et al., 2014), (Fontaras et al., 2008). Consequently, employing multiple energy sources optimizes the power generation of maritime transport, thereby enhancing its capability to achieve high efficiency. Consequently, recent research has explored hybrid propulsion systems for maritime transportation. For instance, Dedes et al. (2016) examined the use of a diesel-battery hybrid propulsion system in a large oceanic bulk carrier. The results showed that the efficiency of the system increased considerably. Consequently, fuel usage decreased by approximately 2%–3%, and CO₂ and NO_x emissions decreased by approximately 5%–7%. Similarly, Boumann et al. (Bouman et al., 2017) reported that hybrid propulsion systems can reduce CO₂ emissions by 2%–45%. Further, a study by Sciberras et al. (2015) introduced a hybrid propulsion system for ships and found that fuel usage and emissions decreased by 44%. In addition, Baccioli et al. (2021) investigated a diesel marine engine with a molten carbonate fuel cell propulsion system. The authors used CO₂ emissions generated by a diesel engine to run a fuel cell. Consequently, the efficiencies increased by 0.8% and 4.9%, respectively, based on the specific system configuration.

In short-trip maritime transportation, pneumatic propulsion systems that utilize compressed air to generate thrust offer distinct advantages over conventional fossil-fuel systems. These systems utilize the expansion of compressed air to generate motion. Compressed air is utilized in many applications such as energy storage (Alami et al., 2022a), cooling (Alami et al., 2022b), (Alami et al., 2023), and cogeneration (Vieira et al., 2021). Their environmental benefits and low-carbon footprint stem from their reliance on clean and abundant compressed air, promising reduced emissions and pollution, which are critical for preserving marine ecosystems (Fang et al., 2021). In addition, the simplicity of pneumatic systems translates to lower maintenance costs and enhanced reliability, which are essential factors for harsh marine environments. Moreover, their capability of instant power and acceleration makes them suitable for scenarios requiring rapid bursts of speed. Alami et al. (2021) assessed the technical feasibility of an all-air vehicle. The experimental results showed great potential for the utilization of such vehicles with speeds reaching 14 km/h and a power of 0.7 hp at a pressure of 5 bar. Another compressed air vehicle showed adequate and economic performance with a work output of 1.014 kW and a torque of 11 N ∙ m at a pressure of 9 bar (Xu et al., 2021a). Ramasubramanian et al. (2021) studied the performance of a pneumatic compressed-air system with various vane angles and casing sizes. The experimental results indicate an average running time of 7 h at a pressure of 3 atm. Pneumatic motors are also used in hybrid propulsion systems. For example, an auxiliary pneumatic motor exhibits an energy efficiency of 62% and contributes a power value of 0.4 kW (Xu et al., 2021b).

This study introduces a novel approach to maritime propulsion, focusing on the use of pneumatic systems, particularly in ferry boats. Unlike most existing studies that focus on electrical or hybrid propulsion, this study explores the benefits of pneumatic motors, which are known for their rapid response, durability, and ease of adoption in existing vessels. An experimental rig was constructed to compare the performance of this setup with that of an electrical propulsion system powered by electrochemical batteries (lead-acid). The main objective is to compare the thrust forces produced by the two systems using a load cell. This study reports the effects of varying the pressurized air tank capacity, pressure, and discharge rate on the thrust force. In addition, a lifecycle analysis was conducted to examine the environmental impact and energy consumption of both propulsion systems, thereby computing any reduction in carbon dioxide emissions achieved using the pneumatic system. This study paves the way for the adoption of renewable and sustainable maritime transportation systems by positioning pneumatic motors as practical, effective, clean, and sustainable alternatives to traditional propulsion systems.