Which of the following is NOT an installed DC system onboard?

The correct answer identifies the hydraulic system as not being an installed DC (Direct Current) system onboard. This is due to the fact that hydraulic systems generally rely on fluid power to operate machinery and do not specifically utilize direct current electricity for their functioning. Instead, they use hydraulic fluid to transfer energy, which is quite different from electrical systems.

In contrast, FM200 (HFP), water mist systems, and firemain systems are all part of fire protection measures that can involve electrical components or systems that can run on DC power. FM200 is a clean agent fire suppression system that may utilize electrical control panels, while water mist systems may also have electric pumps and controls for operation. The firemain system, which is crucial for fire safety and water supply aboard vessels, often incorporates electrically-driven pumps and systems to ensure operational readiness during emergencies.

Understanding the unique applications and operational principles of each system helps differentiate them, particularly in terms of their reliance on direct current electricity.