Question 69 3AE01 - Third Assistant Engineer

The Correct Answer is C ### Explanation for C (Operating in normal mode) In a typical marine fuel oil system setup, "normal mode" refers to the stable, routine operation of the vessel, which usually involves the main engine running on Heavy Fuel Oil (HFO). Valves 4 and 5, in many fuel system diagrams (such as those illustrating transfer pumps, purifier inlets, or changeover stations), often represent critical cross-connection or isolation points between different fuel grades (HFO and DO) or redundant systems. For the system to operate safely, efficiently, and without the risk of contaminating the fuel systems (e.g., mixing HFO and DO), any non-essential cross-connection or bypass valves must remain **closed** during normal, stable operation. Therefore, if valves 4 and 5 are segregation valves, they would be closed when the vessel is operating in normal mode. ### Explanation for Incorrect Options **A) Operating the main engine on DO.** If the engine is operating on Diesel Oil (DO), the DO line to the service tank or engine manifold must be open. If Valve 5 (or 4) controls the flow of DO, that valve must be **open**. Thus, both valves cannot be closed. **B) Loading the HFO bunkers.** Bunkering involves the movement of large volumes of fuel into the storage tanks. This process requires opening specific transfer and filling valves. Depending on the exact position of Valves 4 and 5 in the illustration, at least one of them (related to the transfer or overflow path) would likely need to be **open** during this operation. **D) Operating DO purifier on HFO.** While this statement is technically contradictory (a DO purifier is usually cleaned for DO service), if the intention is to use the purifier designated for DO to clean HFO, the HFO feed line to that purifier must be **open**. If Valve 4 (or 5) is the HFO feed line, it must be open, meaning both valves are not closed.