The short answer is nothing. They are one in the same… A drift boat (as seen above) is a type of dory, but not all dories are drift boats.
Ask a few different folks in the fishing and boating world, though and you’ll get a handful of different answers. This argument comes up time and again. I’m in the habit of calling my hard sided fishing boat a dory and that, occasionally starts an argument that it’s not, but rather a drift boat.
Now if you look up the words drift boat, online it’s characterized as “an evolution of the open-water dory, converted for use in rivers. The design is characterized by a wide, flat bottom, flared sides, a narrow, flat bow, and a pointed stern.” Note the words, “evolution” and “open-water.” A drift boat is not decked, thus will sink if swamped with enough water, but it is a dory.
While the definition for a dory is, “a small, shallow-draft boat, about 5 to 7 metres or 16 to 23 feet long. It is usually a lightweight boat with high sides, a flat bottom and sharp bows. They are “easy” (my quotes) to build because of their simple lines. For centuries, dories have been used as traditional fishing boats, both in coastal waters and in the open sea.”
“Strictly speaking, the only true defining characteristic of the dory is that it is planked up with wide boards running fore-and-aft; “It should be well understood, that it is the dory’s special mode of construction, not its hull shape, that sets it, and its related sub-types apart from other boats”.
Whitewater dories are decked and meant to be run in white water. They can and will stay floating even if flipped upside down or completely covered by a wave.
Drift boats and white water dories were born out of the tradition of fishing boats on the open sea hundreds of years ago. But… while a drift boat can most certainly be a dory, not all dories are drift boats. If I’m wrong, let me know your argument. I’d be keen to hear it.