What characteristic easily identifies a Scotch Marine boiler?

The Scotch Marine boiler is easily identified by its cylindrical internal furnace design. This distinctive feature allows for efficient heat transfer and steam generation due to the large surface area provided by the cylindrical shape. The internal furnace design creates an effective combustion space, contributing to better fuel efficiency and smoother operation.

While the other characteristics mentioned might be present in various boiler designs, they do not specifically define the Scotch Marine boiler. For instance, many boilers may have flat designs or utilize water tubes, but these traits are common across different boiler types. Similarly, vertical designs exist in other boiler types as well. The key element that sets the Scotch Marine boiler apart is its cylindrical internal furnace, which plays a crucial role in its operation and efficiency.