Performances of a ducted podded propulsor for autonomous boat. Part I: calm water experiments

The present work, which is part of the CNR-INSEAN activities within the Italian Flagship Marine Research Project "Ritmare", concerns the design procedures and open water tests in calm water of a full-scale propulsive system for an autonomous vehicle. The chosen SWATH type concept is an appealing solution because of the capability to operate on a wide range of speeds (varying from Fr=0.1 during the measurement stage to Fr=0.5 during the transfer stage) and with reduced accelerations in moderate seawave. Among several propulsive solutions, an azipod with ducted propeller has been selected. Azimuthal POD propulsor ensures the steering thrust and the gondola provides the electric motor housing. The ducted propeller configuration represents a trade-off solution between a limited variation of performances for different operating conditions and an improved safety in shallow water operation by preventing propeller accidents. Four propulsive layouts, isolated propeller, ducted propeller, podded propeller and ducted podded propeller are considered and a detailed experimental investigation has been conducted to properly evaluate their contribution to the global performances of the propeller system.