The location of a vessel's center of flotation during operation at sea plays an important role in the vessel's longitudinal stability. The ability to accurately estimate the location of the center of flotation improves safety monitoring as it indicates how changes in the distribution of weight affect the vessel. In this paper, we propose a novel method for estimating the longitudinal location of a vessel's center of flotation in waves using acceleration readings taken simultaneously at different locations along the length of the vessel. Specifically, we recorded accelerations of an autonomous surface vehicle (ASV) in a towing tank. The ASV was operated in head and following regular waves, which were kept at a constant wave height of 0.12 m while the wave frequency was increased from 0.5 to 0.8 Hz at increments of 0.1 Hz. The results show that multiple acceleration measurements can be used to correctly determine the center of flotation of a vessel in waves. In this experiment, the estimated location of the center of flotation varied as expected based on the longitudinal asymmetry of the ASV and the difference between head and following waves, demonstrating the effectiveness of the proposed method. In addition, the results were validated using the vessel's recorded pitch motion.