Ok, first off, this move is pretty awesome:
[[File:Gomu gomu no red hawk.jpg|300px]
But seriously, how the hell did he do it? He punched clean through Hody, blew him, and with only one hit! Underwater, dammit! I know it has something to do with the Gear Second, but I cant picture Luffy being able to create an explosion underwater. (I am still wondering how he produces visible steam, which is evaporated water, quite some distance beneath the surface.) So.....how did he do it?