Proceedings of the Institute of Acoustics EXPERIMENTAL INVESTIGATION OF A MONO-HULL MODEL BOAT WITH WAVE-LIKE AQUATIC PROPULSION VV Krylov E Porteous Department of Aeronautical and Automotive Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK 1 INTRODUCTION The most common method of aquatic propulsion used in existing marine vessels is a screw propeller. It has a simple design and is capable of propelling marine craft at high speeds. However, the conventional propeller has a number of disadvantages. In particular, these are cavitation and generation of the associated under-water noise. The collapsing cavitation bubbles also cause a gradual destruction of propeller blades, which limits their service life. For many years scientists and engineers were trying to create propulsive systems that could be alternatives to a propeller. Some of them were looking for inspiration in nature, trying to simulate fish swimming using elastic wave propagation in different submerged structures. In particular, it turned out that the wave-like motion used by stingrays resembles closely the propagation of localised flexural waves along tips of submerged elastic wedges or plates of finite width 1,2 . As a result, it has been suggested to use these waves for aquatic propulsion of small marine craft, e.g. submarines 1 . The important features of localised flexural waves for wave-like aquatic propulsion is that their energy is concentrated at the tips of the plates or wedges, which means that the main body of the craft remains isolated from their vibrations. This makes it possible to apply this type of wave motion for propulsion of manned marine craft. In comparison with a propeller, the wave-like aquatic propulsion has the following advantages: it does not generate underwater noise and it is safe for people and marine animals. The first practical realisation of this type of propulsion has been made recently using a small model catamaran employing localised flexural waves propagating in a vertical rubber plate 3,4 . Note that earlier designs of wave-like propulsion using usual (non-localised) flexural waves 5,6 caused craft body rocking in response to plate vibrations. Therefore, these designs were unsuitable for manned marine craft. The present paper describes the design and experimental testing of a small-scale mono-hull model boat propelled by a localised flexural wave propagating along a rubber plate of finite width forming the boat’s keel. Tests include measurements of boat’s speed, thrust and propulsion efficiency. The model boat under consideration is fully autonomous and robotically controlled. 2 CRAFT DESIGN AND CONSTRUCTION The first stage in the design and construction of the considered model boat, that will be also called “Biomimetic Robotically-operated Aquatic VEhicle” (BRAVE), was to define the propulsive plate excitation method. The chosen design implements a leading edge excitation mechanism. Excitation of the leading edge in this manner causes localised wave propagation throughout the length of the propulsive plate towards the trailing edge. Ideally, the propulsive plate should have a wedge-like profile to provide isolation of the flexural wave energy from the craft’s body. This however was not implemented in this investigation due to the time and cost constraints. Like in the earlier work 3,4 , a wedge was therefore replaced by a plate of constant thickness, with one of its horizontal edges being clamped and another one remaining Vol. 30. Pt.2 2008 Page 163