Table 1. Noise peaks and probable sources.		

Frequency (Hz)	Acoustic source	Electrical source

9	 DC motors driving propeller shafts (bull gear ratio 6.76:1)	
15	Main engines (900 rpm)	
18	DC motors driving propeller shaft (first harmonic)	
29	Pumps and compressors (1750 rpm)	
30	Main engines (first harmonic)	
45	Main engines (second harmonic)	
60		Regulated ship's power
60	Main engines (third harmonic)	
61		Unregulated ship's power
75	Main engines (fourth harmonic)	
90	Main engines (fifth harmonic)	
105	Main engines (sixth harmonic)	
120	Main engines (seventh harmonic)	
120		Regulated ship's power (first harmonic)
122		Unregulated ship's power (first harmonic)
135	Main engines (eighth harmonic)	
150	Main engines (ninth harmonic)	
165	Main engines (10th harmonic)	
180		Regulated ship's power (second harmonic)
183		Unregulated ship's power (second harmonic)