The Marquardt Corp. of Van Nuys, Calif., has named the Marconi International Marine Co. Ltd. of Great Britain as its authorized sales and service representatives for its new line of Doppler sonar navigation systems and related marine electronic products. The announcement of the appointment, which was made by J. D. Wethe, president of Marquardt, noted that Marconi Marine and its subsidiaries operate more than 70 facilities at major seaports throughout the world. Marquardt Corp. is a subsidiary of CCI Marquardt.