I like the guy on the right. He's affable-lookin'. Reminds me of a guy I adore, too, even though he doesn't really look a whole lot like him.
The back is blank (not "postally used"), with a blank stamp box, but the nature of the card itself suggests it's most likely from somewhere between about 1910 and 1930. The ship they appear to be on, the Kronprinz Wilhelm, has a fascinating story that has me wondering about these fellas even more. (Are they really on it? Or are they posing with a life preserver from it? They sorta "look" German, don't they? And their clothes seem of the 1910--1915 variety, yes?) The ship did end up in the U.S., having stumbled into the Chesapeake in 1915, after quite a few adventures, and later became the USS Von Steuben, thenceforth and thereas serving on the American side until the end of WWI. Its original German crew (and their many prisoners) were thus in the States at one point. Was the postcard from before that, and just kept with someone and handed down until nobody was left who wanted it or knew the guys in it? That's my bet. It was the guy on the right, and I'm now going to assume that premise and start imagining his life story.
(Did I mention that I love old postcards?)