Under-water exploration and surveillance requires a significant amount of onboard power for unmanned underwater vehicles (UUVs). The main focus of researchers and scientists is to design small, versatile UUVs, which can relax the power requirement onboard and hence increase the mission time. The paper proposes to develop a spherical underwater robot that can employ a docking or soft grounding behavior. To obtain this mechanism the spherical underwater robot should have the capability of self-ballast. By optimally positioning itself and sitting on the bottom, the spherical underwater robot can be placed in sleep mode, with only monitoring sensors awake, thereby harvesting power from the water current through dynamo based rotor blades. After the evaluation of different depth control strategies and research for commercially available UUVs, a concept was found by several comparisons. A diving system has been designed, built and implemented. Additionally, a dynamic model of the diving system has been developed and tested, allowing variable depth control. A Spherical Underwater Robot (SUR) is designed to perform test runs in a test pool. The development of the dynamic model is carried out by a simulation implemented in the MATLAB / Simulink software platform. Experimental test were conducted to validate the dynamic model. [ABSTRACT FROM PUBLISHER]