Which type of boiler is a scotch marine boiler?

A scotch marine boiler is classified as a fire tube boiler. In fire tube boilers, hot gases produced from combustion pass through tubes that are surrounded by water, allowing heat to be transferred effectively to the water, which then generates steam. The scotch marine design specifically features a number of large-diameter fire tubes that run through the boiler's shell, creating a compact and efficient heating surface.

This design is particularly efficient for producing steam or hot water due to its ability to generate a significant amount of steam in a relatively small footprint while being easy to maintain. Fire tube boilers, such as the scotch marine type, are typically found in applications that require a robust steam capacity with lower maintenance needs.

The other types mentioned do not match the characteristics of a scotch marine boiler. For instance, a two pass boiler refers to a specific design where flue gases travel through the boiler in two passes, and while it may have a fire tube construction, it doesn't specifically pertain to the scotch marine type. Copper tube boilers, on the other hand, use copper tubes rather than steel tubes and have different thermal properties and applications. Finally, four-pass water tube boilers have a different operating principle, wherein water circulates through tubes that are heated by flue