The inspection of ship hull thickness and marine structures using underwater vehicles has merged as a unique and challenging application of robotics. The problem poses rich questions in physical design and operation, perception and navigation, and planning, driven by difficulties arising from the acoustic environment, poor water quality and the highly complex structures to be inspected. This technological problem has motivated to a group of researchers of the Federal University of ABC for the development of a Hybrid Remotely Operated Vehicle (HROV) having ultrasonic transducers to check the thickness of the hull and possible cracks. This vehicle is classified as a hybrid robot due to two operation modes: free-flying and crawler. While the first mode the vehicle uses the thrusters at the second mode this use the motorized tracks for its locomotion on the surface of the ship hull. The adherence to the ship hull is guaranteed by applying a force normal to the hull surface from vertical thrusters.

This work describes in detail the mechanical design and reports the drag hydrodynamic coefficients of the HROV. The results of both structural and hydrodynamic simulations of the vehicle verified its operation at maximum velocity of 1 m/s with low hydrodynamic drag. The drag coefficients of the vehicle for surge, sway and heave motions are observed not to depend on the tested range of Reynolds numbers, i.e. for  a result important for the model-based control system design.

hybrid robotic vehicle, underwater inspection, mechanical design, drag coefficients.