Not silly. There are supercavitating and ground effect vehicle designs that reach subsonic speeds(300+ km/s). Most are torpedos, like the VA-111 Shkval[0], or m

Not silly. There are supercavitating and ground effect vehicle designs that reach subsonic speeds(300+ km/s). Most are torpedos, like the VA-111 Shkval[0], or military craft, but the potential is there for a very fast boat-like thing. [0] http://en.wikipedia.org/wiki/VA-111_Shkval http://en.wikipedia.org/wiki/VA-111_Shkval