What is defined as the total heating surface of a naval boiler?

The total heating surface of a naval boiler is defined as the portion of the heat transfer tubes exposed to combustion gases. This is crucial because the heating surface is where the transfer of heat from the combustion gases occurs. The area that constitutes the heating surface includes all surfaces that are in direct contact with the flue gases, allowing for effective heat exchange necessary for boiling water and generating steam.

In a naval boiler, maximizing the heating surface is essential for efficient operation. The more area available for heat transfer, the more steam can be produced in a given time, which is vital for the performance of the propulsion and power systems on a vessel. This definition specifically emphasizes the roles of the heat transfer tubes, which are integral components of the boiler's design, as they carry water and steam and facilitate the transition of heat absorbed from the combustion process.

The other options do not correctly capture the comprehensive nature of the total heating surface as it pertains to heat exchange. For example, merely stating the area that generates steam or defining non-contributing sections does not address the full scope of heating surfaces integral to the boiler's function. The focus on combustion and heat transfer is fundamental to understanding how a naval boiler operates effectively.