Noise from boats is often loud and can reach apartments or the offices located near Tokyo's canals. The aim of this research is to create quiet spaces in buildings using a sound damping system with adaptive noise control. This system does not use a reference microphone because there is sometimes no place to put it outside a window. We propose a tap length for an infinite impulse response (IIR) filter as an adaptive noise control system for reducing boat noise. In this paper, we analyzed the characteristics of boat noise as well as the adaptive damping filter. We investigated the step size and the tap numbers of the IIR filter to improve the performance of the adaptive noise control system with a digital signal processor. The results showed that boat noise is composed of a peak frequency and some other dominant frequencies caused by the boat engine which produces long continuous noise. We therefore designed the IIR filter to adapt to these frequencies. As a result, the system effectively reduced boat noise in a computer simulation.