The maritime industry is facing increasing pressure to reduce its carbon footprint and comply with stringent emissions regulations as part of the UK's Clean Maritime Plan and the global drive toward net-zero emissions by 2050\. This project will develop a novel hybrid fuel system, designed to retrofit on vessels ranging from 40-100ft. These vessels, including fishing boats, workboats, offshore survey and research vessels, are a significant part of the commercial maritime sector, particularly in coastal regions such as the South West of the UK. Retrofittable hybrid systems offers cost-effective alternatives to replacing entire engines with lower or zero-emission alternatives which can be prohibitively expensive for many operators, especially those with older vessels. By retrofitting existing engines with our hybrid fuel system, operators can achieve between 10-30% fuel savings and reduce emissions by up to 85%. This solution also improves engine efficiency and extends engine life, resulting in lower maintenance costs. HotCell's innovative design of hybrid fuel system makes it simpler, more cost effective, and more reliable than those currently on the market. With rising fuel prices and the push for greener technologies, our system provides a practical, affordable pathway for vessel owners to meet emissions targets and improve their operations, in a timescale suited to meet the regulatory pressures of the landscape. It aligns with both national and international decarbonisation efforts while supporting the economic viability of small to medium-sized maritime businesses, democratising access to green technologies. Throughout the project, we will take our prototype from Technology Readiness Level (TRL) 4 to a market-ready product at TRL7\. This will involve testing the system on real-world vessels in partnership with operators in the South West, ensuring that the technology meets the practical needs of end users. Our supply chain is based wholly in the South West, from suppliers to customers, and includes both industry and academic expertise, meaning the economic impact for this project goes directly into the local economy, both during the project and from the subsequent market expansion of our product. The design of this system can be scaled to suit transoceanic cargo vessels, and beyond the maritime sector to industrial feedstock, plant machinery, transporation, and aerospace.