CMOVE- a versatile underwater vehicle for seafloor studies

CMOVE is a wheel driven underwater vehicle that has been developed to conduct measurements at the sediment/water interface. It can be either operated as an autonomous vehicle or tethered with a fibre optic cable. In the current configuration the power supply allows for covering a range of the order of 100's of meter and a deployment time of about 12 hours using the type of scientific payload that is currently installed. During a cruise with the German research vessel MERIAN in the Black Sea in April 2010 ten deployments of the system has been carried out. All missions were completed successful and a significant amount of technical data to judge about the performance of the system has been collected. As a general conclusion it can be said that the vehicle concept has been proven to be very successful in regard to the payload integration and steering capability. The later characteristic is very important as one of the main scientific goals is to investigate the spatial variability of biological activity which is reflected in the patchiness of the sediment surface structure. To probe the actual spot of interest and not just following a preprogrammed pattern is of utmost importance as the spatial variability of the processes that occur at the sediment/water interface is largely unknown up to now. It is very important that the vehicle does not disturb the anticipated measurements for instance by exerting too much force on the sediment or by dispersing extensive amounts of dust with the propulsion system. It could be verified by visual inspection with a high resolution camera that the amount of redeposited sediment was negligible. In regard to the performance of the developed wheels the underwater images of the tracks showed that the slip of the wheels was very low. This demonstrates a high power efficiency of the propulsion system. Also the weight distribution is critical as this will influence the wheel performance and the steering of the vehicle. The individual dive was carried out by deploying the system with a depressor weight which decoupled the vehicle from the ship motion and the cable drag. The operation range was limited to a diameter of 50 m around the depressor. For reaching areas outside the range the ship followed the vehicle in the direction of motion making use of a very precise operating dynamic positioning system. In this paper the basic vehicle concept will be recapitulated and compared with the achieved results. Furthermore, the range of applications where this vehicle concept is best suited and outperforms other approaches are described.