Exam Questions And Correct Answers

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

Question 1: The main function of a ship’s centrifugal pump is to:

• Compress air
• Move fluids by centrifugal force
• Convert electrical energy to mechanical energy
• Heat fluids

Rationale: Centrifugal pumps use a rotating impeller to impart velocity to a

fluid, converting it to flow, which is the primary mechanism for moving liquids.Question 2: In a steam turbine, the purpose of the governor is to:

• Control the lubrication system 1 / 4

• Adjust condenser pressure
• Regulate turbine speed
• Prevent corrosion

Rationale: The governor senses speed changes and adjusts steam flow to

maintain the turbine at a constant speed.

Question 3: Which of the following is the main cause of cavitation in

pumps?

• Excessive lubrication
• High fluid viscosity
• Low inlet pressure
• Overheating

Rationale: Cavitation occurs when the pressure at the pump inlet drops

below the vapor pressure of the liquid, causing vapor bubbles that can damage the impeller.Question 4: The purpose of a feedwater economizer in a boiler system is to:

• Increase steam pressure
• Preheat feedwater using flue gas
• Reduce boiler water level
• Remove dissolved oxygen

Rationale: Economizers recover heat from flue gases to preheat boiler

feedwater, improving thermal efficiency. 2 / 4

Question 5: The most common material for marine piping in freshwater

service is:

• Cast iron
• Copper-nickel alloy
• Aluminum
• Bronze

Rationale: Copper-nickel alloys resist corrosion and are widely used for

seawater and freshwater piping systems on ships.

Question 6: Which of the following is a primary function of the main engine

crankcase ventilation system?

• Lubricate bearings
• Remove blow-by gases
• Increase fuel efficiency
• Cool the engine

Rationale: Blow-by gases escape past the piston rings; the ventilation

system removes these gases to prevent contamination and pressure buildup.

Question 7: Which type of fuel is typically used in marine diesel engines

above 10,000 HP?

• Marine gas oil
• Heavy fuel oil (HFO)
• Kerosene
• LNG 3 / 4

Rationale: Large marine diesel engines are designed to burn heavy fuel oil

due to its low cost and availability.Question 8: The main purpose of the ship’s bilge system is to:

• Supply potable water
• Cool engines
• Remove accumulated water from compartments
• Provide firefighting capability

Rationale: The bilge system collects and pumps out water that

accumulates in the lowest part of the ship to maintain buoyancy and safety.

Question 9: In a marine refrigeration system, the function of the expansion

valve is to:

• Compress refrigerant
• Reduce pressure and control flow
• Absorb heat
• Condense refrigerant

Rationale: The expansion valve lowers the refrigerant pressure, allowing it

to evaporate and absorb heat in the evaporator.

Question 10: What is the primary function of a turbocharger on a diesel

engine?

• Reduce exhaust emissions
• Lubricate the engine
• / 4