## 1 Introduction  
The urgency for sustainable energy alternatives, fueled by a burgeoning global population, has thrust renewable sources into the forefront of energy discourse [1; 2; 3]. Among these alternatives, hydrokinetic energy emerges as a compelling solution [4; 5], harnessing the kinetic motion of water bodies like rivers and oceans [6; 7]. Its ability to mitigate the deleterious environmental impacts associated with conventional fossil fuels renders it an economically viable and environmentally friendly asset [8; 9; 10]. However, despite its substantial potential, the practical implementation of hydrokinetic energy technology remains relatively unexplored, necessitating innovative strategies to facilitate its effective utilization within the energy sector [11; 12]. Driven by the finite nature of traditional energy reserves [13; 14], the pursuit of alternative sources has catalyzed the development of hydrokinetic turbines [15; 16]. Extensive research in hydrokinetic energy conversion has delved into various turbine configurations [17; 18], spanning horizontal-axis [19], vertical-axis [20], cross-flow [21],and oscillating-hydrofoil designs [22]. Notably, studies have revealed the superior performance of hydrokinetic turbines compared to their wind counterparts [23; 24; 25], with horizontal-axis turbines emerging as the pre-eminent choice globally [26; 27; 28]. In contrast to wind turbines mounted on towers, horizontal-axis hydrokinetic turbines are often secured to the seafloor [29; 30; 31], resembling airborne wind turbines in their design and placement [32; 33; 34]. Similar to the developmental trajectory of wind turbines, empirical validation through systematic experimentation is paramount for comprehending the behavior of hydrokinetic turbines and optimizing their performance [35; 36]. In response to this need, a novel testing approach has emerged, utilizing towing tanks that are commonly employed in maritime engineering for ship design and propulsion research [37]. This approach focuses on the conversion of ocean currents' kinetic energy [38; 39; 40], emphasizing the commonality with horizontal-axis turbines used in wind energy [41]. Recognizing the divergence in principles, such as free surface effects and cavitation [42; 43; 44], specialized numerical methods have been developed and validated [45; 46]. These include simulation tools grounded in Blade Element Momentum (BEM) theory, demonstrating satisfactory representations of experimental turbine performance and offering confidence in their applicability for marine current turbine development [47]. This paper introduces a groundbreaking methodology for the dynamometer testing of hydrokinetic turbines, propelling the field towards standardized empirical assessment [48]. By leveraging towing tanks as a testing platform and integrating sensors to capture vital parameters, this experimental framework not only quantifies energy consumption, but also facilitates the extraction of essential hydrodynamic characteristics, such as torque and power generation, thereby fostering further advancements in the field [49]. Additionally, this paper sheds light on the development of an affordable hydrokinetic turbine tailored for towing tank experimental validation and proof-of-concept demonstrations [50; 51; 52]. This accessible turbine model serves as a valuable testbed for evaluating design concepts, optimizing performance, and validating numerical simulations through controlled experiments, ultimately contributing to the maturation and widespread adoption of hydrokinetic energy technologies [53; 54]. In this study, we aim to advance hydrokinetic energy conversion technology by focusing on small-scale horizontal-axis underwater OCTs based on rising global energy challenges. We integrate mathematical modeling with experimental testing in our research. Our major goal is to accurately evaluate OCT performance, aided by the development of a mathematical model, by establishing correlations between power generation, force, and turbine motor rotational speed.