Translation guide
A steamboat is a boat propelled by a steam engine. In Japanese, the most common term is 蒸気船, but historical or specific types may use other words.
A boat powered by a steam engine, typically used historically for transport or leisure.
The standard, neutral term for a steamboat. Suitable for most contexts.
The steamboat went down the river.
A slightly more formal or technical term, often used in historical or official contexts.
A steamboat is anchored at this port.
A steamboat propelled by paddle wheels, often associated with 19th-century riverboats.
A small steam-powered boat, often used for short trips or as a tender.
Borrowed from English 'launch', refers to a small steamboat. Somewhat dated.
We went around the lake on a steam launch.
Both mean steamboat, but 蒸気船 explicitly includes 'steam' (蒸気), while 汽船 can sometimes refer to any steam-powered vessel, including ships. In modern usage, 蒸気船 is more common for historical or recreational boats.
I saw a model of a steam paddle boat at the museum.