- You may also be looking for the descriptor, Class Y.
Ships of this class were usually armed with a single low-yield plasma cannon; however, most captains had the weapons updated to defend against pirates. They were able to haul 20 kilotons at a maximum speed of warp 1.8 with the original warp engine. The ships could be refitted with a warp three engine to make them ten times faster. The crew and family complement of a Y-class cargo ship was approximately two dozen. The Y-class was slightly larger than the the J class, but overall, the same basic design. (ENT: "Fortunate Son")
Ships of the class
Several vessels of this class appear in the game Star Trek: Legacy.