Ambient noise measurements were carried out on two different type cutter suction dredgers whose pumps were driven by a diesel or by a gas turbine engine. It was recognized that the sound propagations obtained from the measurements agreed with the theory of a point sound source. The sound power levels caluculated by the theory amounted to 139dB and to 112dB in A scale. The frequency at which the highest noise level was measured agree with the explosion frequency of the diesel engine or the gas generator. According to the fact, it is concluded that the each ambient noise field was produced by the noise radiated from the exhaust pipe of the engine. Adding to the previous measurements, the ambient noise measurement of the discharge pipe line was also carried out. In this case, the theory of a infinite line sound source could be adapted to estimate the sound power level. The sound power level per unit length of the pipe line reached to 90dB in A scale.