This study presents a research methodology and test setup to analyze different types of recreational fins for specific tasks: beginner recreational swimming, deep-water diving, and sports swimming. The fins tested were Aqualung, Scubapro, and Exotech. The primary goal is to present the diving fins research methodology, experimental results, and conclusions. The study achieves high reliability in real-world conditions by combining experimental design with mathematical models based on hydrodynamic similarity. Key to this approach is conducting methodologically sound experiments on a controllable object, allowing precise energy measurements of the swimmer's leg. Despite the challenges posed by the variable thrust force of diving fins in different leg positions, this method remains the most reliable way to integrate experimental data with hydrodynamic theories in comprehensive, multivariate research. Presented results show that fin energy efficiency strongly depends on the interaction between fin geometry, flexural stiffness, and swimming style, with different fin designs achieving maximum efficiency under different operating conditions