The subsea exploration of complex and challenging areas has increased the need for advanced robotic frameworks, such as cable -based parallel manipulators (CPMs). Known for their flexibility and precision, CPMs are essential for performing detailed tasks underwater. In submarine environments, handling external underwater forces presents a significant challenge, necessitating the optimization of cable tension for effective operation of CPMs. Additionally, achieving a balance between an increased workspace volume and improved manipulator stiffness is crucial. Addressing these challenges, this article presents a design and optimization approach for CPMs. The focus is on the eight- and ten -cable configurations, specifically chosen for their optimal balance of complexity and control. To enhance the efficiency and effectiveness of CPMs in these demanding environments, the article proposes several optimizations, including adjustments in workspace dynamics, cable tension, system layout, and manipulator stiffness. The proposed methodology involves innovative approaches, including an adaptation of the Dykstra algorithm, to refine cable tension optimization, and explores layout optimization strategies to achieve an ideal balance between enlarged workspace and enhanced manipulator stiffness. A key aspect of the present research is the stiffness analysis via natural frequencies, establishing an essential link between detailed design choices and overall manipulator performance. The findings reveal that meticulous design and optimization of CPMs significantly enhance operational efficiency, range, and stability in underwater environments. These advancements provide valuable insights for the broader application of cable -based manipulators in complex underwater tasks, establishing new benchmarks in the field and laying the foundation for future innovations in underwater robotic systems.