Exam Questions And Correct Answers

Coast Guard Designated Duty Engineer (DDE) – 4,000 Horsepower Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• Which of the following is the main function of a centrifugal pump?
• Increase the pressure of a fluid B) Increase the velocity of a fluid
• Compress a gas
• Measure fluid flow

Answer: B) Increase the velocity of a fluid

Rationale: Centrifugal pumps convert mechanical energy into kinetic

energy, thereby increasing fluid velocity, which is then converted to pressure in the discharge.

• What is the primary purpose of a boiler economizer?
• Remove scale from the boiler 1 / 4

• Preheat feedwater using flue gas heat
• Increase steam pressure
• Control water level

Rationale: Economizers recover residual heat from flue gases to

preheat feedwater, improving overall boiler efficiency.

• Which type of fuel oil is most commonly used in a 4,000 HP diesel

engine on a Coast Guard cutter?

• Diesel #1
• Diesel #2
• Bunker C
• Marine Gas Oil (MGO)

Rationale: Diesel #2 is standard for medium-speed marine diesel

engines due to its balance of viscosity, ignition properties, and availability.

4. The function of a reduction gear in a marine propulsion system is to:

• Increase engine speed
• Reduce engine RPM to suitable propeller speed
• Convert AC to DC power
• Filter lubricating oil

Rationale: Reduction gears allow high-speed engines to drive low-

speed propellers efficiently without overloading the engine.

• What is the primary purpose of the main engine lubricating oil

system? 2 / 4

• Clean the fuel system
• Cool the exhaust
• Lubricate and cool engine components
• Power auxiliary machinery

Rationale: The lubricating oil system reduces friction and removes heat

from bearings, pistons, and other engine parts.

• Which of the following statements about a marine generator is

correct?

• It converts electrical energy into mechanical energy
• It converts mechanical energy into electrical energy
• It stores electrical energy
• It regulates engine RPM

Rationale: Marine generators are driven by engines to produce

electrical power for the vessel’s systems.

7. When starting a centrifugal pump, it is important to:

• Run at full speed immediately
• Ensure suction line is flooded and pump is primed
• Open discharge fully
• Keep all valves closed

Rationale: Centrifugal pumps must be primed to prevent cavitation

and damage caused by running dry.

• What is the purpose of a bilge alarm system?
• Detect fuel leaks 3 / 4

• Alert crew of water accumulation in the bilge
• Monitor engine temperature
• Control fire suppression systems

Rationale: Bilge alarms warn of excess water in the bilge to prevent

flooding or sinking.

9. In a typical marine steam boiler, the purpose of the superheater is to:

• Preheat feedwater
• Remove scale
• Increase the temperature of steam above saturation
• Reduce exhaust emissions

Rationale: Superheaters raise the temperature of steam to improve

thermal efficiency and prevent condensation in the engine.

• Which type of heat exchanger is most commonly used for

cooling lube oil on marine engines?

• Shell-and-tube condenser
• Shell-and-tube cooler
• Plate heat exchanger
• Air-cooled radiator

Rationale: Shell-and-tube coolers are robust and suitable for high-

temperature lube oil cooling in marine applications.

• What is the purpose of a main engine turbocharger?
• Increase fuel efficiency by burning more fuel
• / 4