We investigate several phenomena at the surface of water, that are either traces of an object, or of a former event. First, we study the cavities formed by explosions at the surface of water. In a large bath, the cavities grow with a hemispherical shape, and then collapse anisotropically, what creates a vertical jet. This evolution results of an energy balance between kinetic and potential energy. Confining the cavities in vertical opened tubes we observe that the cavities never escapes. In a second part, we study the impact of vortex rings on surfaces. We observe that the vortex diameter is doubled in the interaction we the free surface of water, while it expands a lot more in ethanol. This difference comes from the fact that the free surface of water is equivalent to a rigid surface for the ring, what enhances the formation of secondary vortices. The third part deals with the wave drag of submerged spheres. We observe that there is a large discrepancy between the predicted and measured force, in the range where it is large. We measure the waves amplitude and show that taking into account their saturation can correct the theoretical estimation.
