Term: triple-expansion steam engine (maritime)
An engine with three steam cylinders of different diameters. Steam passes from a small-diameter high-pressure cylinder to an intermediate cylinder to a large-diameter low-pressure cylinder. These cylinders power the pistons that drive the engine.
View pictures related to boating at Wisconsin Historical Images.
[Source: "Glossary." Wisconsin's Great Lakes Shipwrecks (http://www.wisconsinshipwrecks.org/)]