Hmmm.... a problem. According to Canney's The Old Steam Navy Vol I, the maximum battery the Pawnee carried was eight IX-inch Dahlgrens in broadside. There are six in that photo alone, all on one side and I'm betting there are more "behind" the camera. This can't be Pawnee. With the apparent size of the armament, I'm tending toward a frigate, possibly Wabash if it's indeed at Charleston... or maybe a heavy sloop like Pensacola et. al.