In this work, an effective energy-saving device is proposed to extract wave energy and convert to useful propulsive thrust for a merchant ship travelling in waves. Eco-Ship was internationally introduced and aimed to reduce carbon dioxide emission generated from ships. The energy-saving device equipped underneath the front part of the ship model of general merchant ships that inspired by marine mammals is investigated in this work. An active control of pitch-oscillating bow fin with NACA0016 section is applied as an effective energy-saving device in this work. Free-running model test using a 1/50th scale model of a container ship was conducted for validating the effectiveness of this device. The ship speed, ship motion, angle of bow fin and power consuming are measured and recorded. There are two kinds of wavelength to ship length ratio of regular wave in the experiments with fixed propeller speed. Based on different heave motion, the different pitch angle of bow fin is controlled to obtain the extra energy from wave. The experimental results shows the feasibility of the energy-saving device when the phase lead of the bow fin pitch motion with respect to its heave motion set in a proper range between 60 degree to 200 degree. When the ratios of wavelength to ship length are 1.0 and 1.3, the maximum of power efficiency improving are around 6.5% and 18.9% respectively. The experimental results demonstrated that the proposed device is effective to enhance ship speed and save energy for achieving the goal of Eco-Ship.