Question 55 QMED01 - Junior Engineer

The Correct Answer is C ### Explanation for C (Slow speed, non-reversing engines) The key characteristics mentioned in the question are: **large merchant vessel**, **direct drive**, and **controllable pitch propeller (CPP)**. 1. **Large Merchant Vessel & Direct Drive:** Historically, large merchant vessels primarily use **slow-speed** two-stroke diesel engines for propulsion. These engines are highly efficient and directly connected to the propeller shaft (direct drive). 2. **Controllable Pitch Propeller (CPP):** A CPP allows the pitch of the propeller blades to be adjusted while the engine speed and direction remain constant. This means the propeller itself can manage forward, astern, and zero thrust without the need for the **engine** to reverse its rotational direction. Therefore, if a vessel uses a CPP, the engine must be **non-reversing**. Combining these requirements, a large merchant vessel utilizing a CPP would be powered by a **slow speed, non-reversing engine**. *** ### Why Other Options Are Incorrect **A) Slow speed, reversing engines:** While slow-speed engines are common in large merchant vessels, the presence of a Controllable Pitch Propeller (CPP) makes engine reversal unnecessary. If the engine *were* reversing, it would typically indicate a Fixed Pitch Propeller (FPP) setup. **B) Medium speed, non-reversing engines:** Medium-speed engines (typically four-stroke) are often used in merchant vessels, but they usually require a reduction gearbox to connect to the propeller shaft, as their RPM is too high for efficient propeller operation. The question specifies **direct drive**, which strongly implies a slow-speed engine setup, making medium speed unlikely in this context. **D) Medium speed, reversing engines:** This option combines the issues of B and A. Medium-speed engines rarely use direct drive (requiring a gearbox), and the use of a Controllable Pitch Propeller (CPP) removes the need for the engine to be reversing.