🔍 Key Concepts

• Astern element function in a marine main propulsion turbine • Difference between impulse and reaction turbine stages • Typical design of a low-power, short‑duration astern turbine compared with the ahead turbine

💭 Think About

• Which type of turbine stage is better suited for occasional use at lower power, with simpler construction and control for going astern? • Among the options, which design is most commonly used as a compact, efficient first stage for taking large pressure drops in one or two stages? • Think about standard marine steam turbine arrangements: what kind of stage is typically placed in the astern casing or astern portion of a main turbine?

✅ Before You Answer

• Be clear on the definition of impulse stage (pressure drop mainly in nozzles) vs reaction stage (pressure drop in both nozzles and moving blades). • Consider which type of stage (impulse or reaction) is most often used for astern elements in marine practice. • Check which option describes a known standard stage type used for first stages and special elements in marine turbines.