The invention relates to a method for classifying one or more watercraft on the basis of the sound waves (2) emitted or transmitted by these craft. In this case, the sound waves (2) are received by an arrangement of waterborne sound sensors of a Sonar receiving installation (4) and processed to form received signals (6). At least one amplitude spectrum (24) is produced from these received signals (6), said amplitude spectrum (24) having one or more sets of frequency lines and possible single lines, from which characteristic craft parameters (28) are determined automatically in a frequency line pattern identification module (26) or manually. Subsequently, the characteristic craft parameters (28) are compared with parameters in a database, with this comparison being rated with a correspondence factor (34). One or more watercraft are determined as a result of the classification, taking the correspondence factor (34) into account. Furthermore, the invention relates to a corresponding device for carrying out the method.