The paddlewheel, often with a weight of some tons, makes a steamboat move. The most important advantage of a paddlewheel-powered boat is the low draught, so the boats could go far up the rivers, even when the water level was very low. This was a very important fact for the frontiers by opening up the continent for settlement.
sternwheel
sidewheel
There are two types of paddlewheels: the sternwheel and the sidewheel. The sternwheel uses to be more effective, but made some problems for the hull construction, especially the wooden ones, because of its heavy weight. Therefore the construction of a side wheeler was easier, concerning to this problem.
On the other hand sidewheelers were necessary e.g. as snagboats (for clearing the river from tree trunks) or as railroad ferries.