Question 50 DDE04 - Designated Duty Engineer - 1000-4000 HP

The Correct Answer is B **Why Option B ("Reduce the load and speed on the engine.") is correct:** When an internal combustion engine experiences overheating, indicated by the alarm, high temperature readings, and excessive expansion/venting of the cooling water, the immediate priority is to reduce the heat being generated. Reducing the engine's load (power output) and speed will significantly decrease the fuel being injected and the work being done, thereby instantly lowering the heat input into the cooling system. This action provides time for the cooling system (pumps, heat exchanger/radiator) to catch up, stabilize the temperature, and allows the operator to safely diagnose the underlying cause (e.g., thermostat failure, pump malfunction, heat exchanger fouling) without risking immediate, severe damage to critical components like the cylinder heads, liners, and pistons. Since the tug is proceeding in open waters and still requires maneuverability (even on one engine), a controlled reduction is preferable to an immediate shutdown, which would leave the tug with only one propulsion unit. **Why the other options are incorrect:** * **A) Add makeup water to the expansion tank:** Adding makeup water to an already hot and expanding system is dangerous and ineffective. The system is already overfull (expansion tank level is high) and venting vapor due to excessive heat. Adding cold water to a superheated system can cause thermal shock, potentially cracking engine components. Furthermore, adding more water will not solve the underlying overheating issue. * **C) Shut down the engine immediately:** While an immediate shutdown will stop heat generation, it should only be done if the temperature is rising uncontrollably, or if there is visible smoke or imminent mechanical failure. If the temperature is high but stable, an immediate shutdown prevents controlled cooling, risks thermal stress during the rapid cool-down period, and unnecessarily sacrifices propulsion power prematurely, complicating the tug's maneuvering capabilities. Reducing load (Option B) is the controlled, initial action before considering a full shutdown. * **D) Drain water from the expansion tank:** Draining water from the expansion tank while the engine is running and superheated is extremely hazardous due to the pressurized hot water and steam. Furthermore, reducing the total water volume in the system will only exacerbate the overheating problem by reducing the heat transfer capacity available to cool the engine components.