The inscription on the stamp gives a Roman Harbor Boat, can’t find an image of a Roman harbour boat on the net.
The ship on the stamp looks more like a medium sized Roman merchant ship from about the third century AD under sail. The sails in that time were made of thick linen or animal skins sewn together.
She is steered by two oars at the stern, one on each side.
Not any oar visible on the stamp, but most probably also possible to row when needed.
Like more info on a Roman harbour boat, when used etc.