My great grandfather served in the U.S. Navy aboard this ship (which I believe is a light armored cruiser) a few years prior to the U.S. entry into World War I. I have no documents about his military service -- and he apparently lied about his age to get in to the navy, so any records might not be in his real name.
His photo is pretty high-resolution, and I've even been able to zoom in and see laundry drying on a line! But unfortuantely there's no markings that I can discern. My guess is that the ship is a Philadelphia class light armored crusier, perhaps the USS Maryland (ACR-8) or USS South Dakota (ACR-9), but I could be wrong. Someone with more expertise in ship architecture might be able to better narrow it down.
Here's the photo, thanks in advance.
Might I recommend paying a visit to the good folks over at /r/warshipporn ? We tend to devour such conundrums with an almost disturbing amount of haste.