It is these early steam-driven river craft that typically come to mind when "steamboat" is mentioned, as these were powered by burning wood, with iron boilers drafted by a pair of tall smokestacks belching smoke and cinders, and twin double-acting pistons driving a large paddlewheel at the stern, churning foam. This type of propulsion was an advantage as a rear paddlewheel operates in an area clear of snags, is easily repaired, and is not likely to suffer damage in a grounding. By burning wood, the boat could consume fuel provided by woodcutters along the shore of the river. These early boats carried a brow (a short bridge) on the bow, so they could head in to an unimproved shore for transfer of cargo and passengers.