Question 55 DDE01 - Designated Duty Engineer - Unlimited HP

The Correct Answer is C ### Explanation of Why Option C is Correct The type of main propulsion diesel engine commonly used in ship-docking tugs, especially those depicted in standard marine engineering illustrations (like the inferred MO-0192, often representing medium-speed or high-speed four-stroke engines such as those by Cat, Cummins, or similar designs), typically features the following characteristics, corresponding to Option C: 1. **Pushrod operated overhead valve engine:** Medium-speed four-stroke engines often use a camshaft located in the cylinder block or crankcase, necessitating **pushrods** and **rocker arms** to actuate the valves in the cylinder head. This configuration is standard for robust, serviceable industrial marine diesels. 2. **Wet cylinder liners:** In these engines, the cylinder liners are directly exposed to the cooling water (jacket water) on their outer surface. This design, known as a **wet liner**, allows for superior cooling and easy replacement, making it standard for high-output marine engines. 3. **Conventional connecting rods:** These engines utilize standard, single-piece connecting rods connecting the piston to the crankshaft journal (also known as a simple or standard connecting rod). Specialized designs like marine-type (often used in very large two-stroke crosshead engines) or articulated (often used in V-engines where two cylinders share one crankpin) are typically not the default for this type of inline or standard V-engine used in tugs unless otherwise specified. ### Explanation of Why the Other Options Are Incorrect **A) This is an overhead cam engine, with jacketed cylinder liners and marine-type connecting rods.** * **Incorrect (Overhead cam):** While some modern high-speed diesels use overhead cams (OHC), the pushrod configuration (C) is more common for the medium-speed, high-durability engines typically found in tug propulsion systems illustrated in basic diagrams. * **Incorrect (Jacketed cylinder liners):** "Jacketed liners" is usually synonymous with "wet liners." However, "marine-type connecting rods" refers specifically to large connecting rods featuring a separate crosshead and slipper bearing (used in slow-speed two-stroke engines), which is incorrect for a tug's propulsion diesel. **B) This is a pushrod operated overhead valve engine, with jacketed cylinder liners and articulated connecting rods.** * **Incorrect (Articulated connecting rods):** Articulated connecting rods (where a main rod and a secondary rod share a crankpin) are used primarily in V-engines to achieve a compact design. While some tug engines might be V-type, the description assumes the most common/conventional configuration. If the engine is an inline engine, articulated rods are not used. Even in V-engines, conventional connecting rods (where the rods are side-by-side on the crankpin) are also widely used. The term "conventional" (in C) is a more universally applicable descriptor. **D) This is an overhead cam engine, with wet cylinder liners and conventional connecting rods.** * **Incorrect (Overhead cam):** As noted for Option A, the pushrod configuration (C) is often the standard configuration implied by basic textbook illustrations of medium-speed marine diesels, making the pushrod description (C) a safer and more frequently correct generalization than OHC (D).