Question 6 OSE02 - Assistant Engineer - OSV

The Correct Answer is A. **Explanation for Option A (Correct):** Option A describes a common configuration for medium-speed marine diesel engines often used in offshore supply vessels (OSVs), which are typically four-stroke trunk piston engines. 1. **Pushrod Operated Overhead Valve Engine:** The illustration (MO-0192, which typically depicts a common medium-speed four-stroke engine like a MaK, Wärtsilä, or similar) generally shows the camshaft located in the engine block (low or mid-level). This location requires **pushrods and rocker arms** to transmit the motion to the valves in the cylinder head, defining it as a pushrod operated overhead valve (OHV) engine, not an overhead cam (OHC) engine. 2. **Wet Cylinder Liners:** Medium-speed four-stroke engines almost universally employ **wet cylinder liners**. A wet liner is directly exposed to the cooling water jacket on its outer surface, ensuring efficient heat transfer. (Note: "Jacketed" is not a standard, precise term in this context; wet or dry is preferred.) 3. **Conventional Connecting Rods:** These engines typically utilize **conventional (or straight) connecting rods** attached directly to the trunk piston. Unlike very large two-stroke crosshead engines, they do not use marine-type (fork and blade) or articulated rods unless they are of a specific V-configuration, but the standard in-line or V-engine trunk piston design uses the conventional rod type. **Explanation of Incorrect Options:** **B) This is a pushrod operated overhead valve engine, with jacketed cylinder liners and articulated connecting rods.** * **Incorrect:** While it is a pushrod OHV engine, the term "jacketed cylinder liners" is vague, and more importantly, **articulated connecting rods** are specific to certain V-engines (like some large Wärtsilä or Pielstick models) where one rod drives the crank directly and the adjacent cylinder rod pivots off the first (master rod). This is not the *standard* configuration implied by a general engine illustration unless specified, making the conventional rod (Option A) the more universally true description. **C) This is an overhead cam engine, with wet cylinder liners and conventional connecting rods.** * **Incorrect:** This engine type is typically **not** an overhead cam (OHC) engine. The camshaft is usually located lower in the block, requiring pushrods to operate the valves. **D) This is an overhead cam engine, with jacketed cylinder liners and marine-type connecting rods.** * **Incorrect:** This engine is not an OHC engine. Furthermore, **marine-type connecting rods** (which are typically defined as the separate piston rod/crosshead assembly used in two-stroke crosshead engines) are not used in trunk piston engines like the one typically found on an OSV.