A shipboard terminal (1) is provided on each of a plurality of boats. This shipboard terminal collects the outputs of a plurality of sensors (3) which detect the state of the boat's engine, plus the output of the GPS unit carried on the board. It periodically compares the outputs of this plurality of sensors with their pre-recorded normal ranges, and displays an alarm when a normal range is exceeded. It automatically transmits to a shore terminal (2), via a portable phone network, the data output from the plurality of sensors and the positions data output by the GPS unit, during each communication time which has been allocated to the boat in accordance with time data contained in the output of the GPS unit. The shore terminal (2) receives this data via the public switched telephone network, and records it. This system facilitates the monitoring, via software, of the state of small leisure craft or coastal fishing boats not exceeding several tens of tons, such boats being operated by crews with little knowledge or experience of marine engines. It thereby promotes the safe operation of such boats.