Dear Friends, I have a problem on fluid mechanics that I can't solve. The question is one boat that has great velocity. In front of it, it's created a wave because of the boat. Now, imagine that this boat has greater and greater velocity. The angle of the wave in the front, at great velocity, will be more orthogonal to the trajectory of the boat. Now imagine that one circle of this wave arrounds the boat. The lines of flux that enter this circle, will be the same they go out (conservation of mass), well, how can be calculated this? There's one formula that says shows the flux that enter and go out one surface is the same that enters and go out the volume. It could be calculate with the navier-stokes formula and the conservation of the mass. The question is about an object that is into a flow, that is arrounded by this flow, and finally one geometric balance. best reggards.