They can be a barge or a narrow boat.
Sunfish
A flat boat is a flat-bottomed boat used to float goods and passengers downriver.
ferryboat
The narrow, flat bottomed vessels that have been used on the Nile River for centuries are a type of long boat. The boats needed either oars or a long pole to get through the water. The boats were made of papyrus reeds or wood.
A bateau is a small, flat-bottomed boat.
A gondola.
A batteau is a small, flat-bottomed boat.
barge
A sampan is a relatively flat-bottomed Chinese wooden boat.
There are narrow flat bottom boats called punts, which are moved with the aid of a long pole. The similar boats in Venice are called gondolas. Small boats may be called skiffs, and the flat-bottom canoes of Louisiana are called pirogues. Large boats are canal boats, or barges.
In "The Adventures of Huckleberry Finn," a scow is a type of flat-bottomed boat used for carrying goods on rivers. It is typically rectangular in shape and has a flat deck.