We propose to bring a better understanding of the interaction between an air-water flow and a floating structure by means of a fast accurate numerical model. Following the 3D low Mach compressible Euler model developed in [14] and previous works from [20], [11] and [13], we are now interested in simulating the motion of a floating structure in an air-water flow. In the context of a fictitious domain, a volumic penalization is applied inside the body to ensure a rigidity constraint through a penalized velocity in order to get the correct motion of the rigid body. The tracking of the solid is insured by the reconstruction of a Heaviside function thanks to a ray-casting algorithm. The validity of our fluid-structure interaction (FSI) procedure is investigated through some examples.