In recent years it has become evident that ocean data in time and space is required to make predictions of environmental changes on earth. As one method of acquiring data, we propose a virtual mooring system using an underwater vehicle, and have developed a full-scale test-bed vehicle called "BOOMERANG" which can glide back and forth between the sea surface and the seabed collecting ocean data. Since the results of field experiment in March 2010 were satisfactory, construction on a prototype vehicle for practical use was begun in April 2010. In order to improve reliability and to enable prolonged use, the performance of various pieces of loading apparatus of the vehicle was improved. This paper presents results of the field experiment and details of the construction of the prototype vehicle for practical use.