DDE – Unlimited HP practice test

Q: How many questions are on the DDE – Unlimited HP exam?

The National Maritime Center's 2026 sample examination for DDE – Unlimited HP has 420 questions across 6 modules: Q620 Motor Plants (70 questions), Q621 Steam Plants (70 questions), Q622 Gas Turbine Plants (70 questions), Q623 Engineering Safety & Environmental Protection (70 questions), Q624 General Subjects (70 questions) and Q625 Electrical - Electronic - Control Engineering (70 questions). Every one is multiple choice with four answers, and you can practice all of them on this page.

Q: What modules are on the DDE – Unlimited HP exam?

The modules are Q620 Motor Plants (70 questions), Q621 Steam Plants (70 questions), Q622 Gas Turbine Plants (70 questions), Q623 Engineering Safety & Environmental Protection (70 questions), Q624 General Subjects (70 questions) and Q625 Electrical - Electronic - Control Engineering (70 questions). Each module is graded separately, so you need to pass every one to pass the exam.

Q: What score do I need to pass the DDE – Unlimited HP exam?

Most USCG exam modules require 70 percent to pass; Rules of the Road modules, where they apply, require 90 percent. Check the specific requirements for your endorsement with the National Maritime Center.

Q: Are these the real questions?

Yes. They are the questions on the National Maritime Center's published 2026 sample examination for DDE – Unlimited HP (modules Q620–Q625), matched to our bank of released U.S. Coast Guard exam questions. The exam you sit draws from the same pools.

Q: Can I take a timed DDE – Unlimited HP practice exam?

Yes. Subscribers can sit any module as an official sample exam in its published order, timed or untimed, with answers revealed at the end. Free accounts can build one 10-question practice exam and answer questions on every module page.

Question 1

You are assigned to a river push boat fitted with main propulsion diesel engines operating on the cycle represented in the polar timing diagram shown in the illustration. In consideration of the direction of rotation, what combustion cycle event occurs from point "A" to point "D"?

Accepted Answer

Intake

Answer

Compression

Answer

Power

Answer

Exhaust

Question 2

Prior to starting the main propulsion diesel engines fitted on your river push boat, the crankcase oil level must be checked. At what checked level would you be required to add make-up oil?

Accepted Answer

When the oil level drops below the ADD mark on the side of the dipstick marked ENGINE STOPPED and OIL COLD.

Answer

When the oil level drops below the FULL mark on the side of the dipstick marked ENGINE STOPPED and OIL COLD.

Answer

When the oil level drops to between the ADD and FULL marks on the side of the dipstick marked ENGINE STOPPED and OIL COLD.

Answer

When the oil level drops to where it is no longer visible on the side of the dipstick marked ENGINE STOPPED and OIL COLD.

Question 3

Prior to starting a main propulsion diesel engine fitted on your salvage tug, it has been determined that the transfer of make-up oil is required. At what checked level should you stop adding make-up oil?

Accepted Answer

When the oil level rises to the FULL mark on the side of the dipstick marked ENGINE STOPPED and OIL COLD.

Answer

When the oil level rises to the ADD mark on the side of the dipstick marked ENGINE STOPPED and OIL COLD.

Answer

When the oil level rises to a level well above the FULL mark on the side of the dipstick marked ENGINE STOPPED and OIL COLD.

Answer

When the oil level rises to the between the ADD and FULL marks on the side of the dipstick marked ENGINE STOPPED and OIL COLD.

Question 4

You are on a salvage tug using main propulsion engines of the type shown in the illustration. Assuming that the piston is properly positioned, what statement represents the procedure for inspection of the compression rings while in place inside the engine?

Accepted Answer

The inspection takes place by removing the appropriate air box hand hole cover and viewing through the resulting opening.

Answer

The inspection takes place by removing the appropriate oil pan cover and viewing through the resulting opening.

Answer

The inspection takes place by removing the appropriate cylinder head valve cover and viewing through the resulting opening.

Answer

It is not possible to inspect the compression rings while in place inside the engine.

Question 5

You are analyzing the data used for trend analysis for one of the main propulsion diesel engines on the ship- docking tug to which you are assigned. The cylinder exhaust temperature of one of the cylinders is significantly lower than the others. When analyzing compression and firing pressure data, however, the numbers are within the normal range for this particular cylinder. What condition would produce these results?

Accepted Answer

Excessive carbon build-up on exhaust pyrometer probe of affected cylinder

Answer

Leaking fuel injector needle valve for affected cylinder

Answer

Leaking exhaust valve on affected cylinder

Answer

Excessive carbon build-up on air inlet ports or valves of affected cylinder

Question 6

The bottom blow valve on a water-tube boiler is usually attached to the __________.

Accepted Answer

boiler mud drum

Answer

floor tubes

Answer

external downcomers

Answer

steam and water drum

Question 7

Which type of energy conversion is associated with an operating steam boiler?

Accepted Answer

Thermal

Answer

Mechanical

Answer

Kinetic

Answer

Specific

Question 8

The purpose of the separating nozzle in the accumulator of a water-tube, coil-type, steam generator is to separate __________.

Accepted Answer

dry steam from the steam and water mixture

Answer

condensate from feedwater

Answer

superheated steam from saturated steam

Answer

sludge accumulations from feedwater

Question 9

In a coil-type forced circulation water-tube boiler, __________.

Accepted Answer

steam demand response is comparatively rapid

Answer

steam is recirculated through heating coils in the boiler

Answer

unevaporated feedwater is discharged through the skim tube

Answer

steam demand response is slow

Question 10

Which of the following statements concerning fire-tube boilers is correct?

Accepted Answer

Combustion gases flow through the tubes.

Answer

Flames impinge on the tubes.

Answer

Water flows through the tubes.

Answer

Combustion occurs in the tubes.

Question 11

Compared to other types of engines, what is the biggest advantage of a gas turbine engine?

Accepted Answer

Highest power-to-weight ratio.

Answer

Simplicity of the control circuits.

Answer

Low power-to-weight ratio.

Answer

Simplicity of installation.

Question 12

The thermal energy added to the gas as it flows through the combustion section has what effect on the gas?

Accepted Answer

Increases volume

Answer

Increases pressure

Answer

Decreases volume

Answer

Decreases pressure

Question 13

An open cycle gas turbine engine is best described by which of the following statements?

Accepted Answer

Working fluids are taken in, transformed, and then discarded.

Answer

Energy is neither created nor destroyed and the cycle is therefore perpetual.

Answer

Energy is added externally.

Answer

Working fluids are taken in, transformed, and then recuperated.

Question 14

The Brayton Cycle is a series of events best described by which of the following statements?

Accepted Answer

Intake, compression, combustion, expansion, exhaust.

Answer

Intake, pressurization, ignition, exhaust.

Answer

Intake, compression, combustion, explosion, exhaust.

Answer

Intake, decompression, combustion, expansion, exhaust.

Question 15

Why is a gas turbine considered to operate on the Brayton cycle?

Accepted Answer

Combustion occurs with no increase in pressure.

Answer

Combustion causes large increase in pressure.

Answer

Combustion causes no increase in volume.

Answer

Combustion causes an increase in total mass flow.

Question 16

The bypass valve on a self-contained breathing apparatus (SCBA) bypasses __________.

Accepted Answer

the regulator in an emergency

Answer

a breathing bag containing excessive pressure

Answer

oxygen to the atmosphere

Answer

the regenerator in an emergency

Question 17

Which of the components listed are interchangeable between different backpack self-contained breathing apparatus produced by various manufacturers?

Accepted Answer

The air cylinder

Answer

The face piece

Answer

The regulator

Answer

All of the above

Question 18

One of the main concerns when fighting a galley fire is __________.

Accepted Answer

the igniting of a grease fire in the range hood ventilation system

Answer

the loss of stability

Answer

spreading of fire through the engineering space

Answer

contaminating food with extinguishing agent

Question 19

When fighting a liquefied natural gas fire, you should __________.

Accepted Answer

secure the source of gas, then extinguish the fire

Answer

use only carbon dioxide

Answer

extinguish the fire, then secure the source of gas

Answer

use only dry chemical

Question 20

Progressive flooding in the engine room may be minimized by securing watertight boundaries and __________.

Accepted Answer

pumping out flooded compartments

Answer

transferring reserve feed water

Answer

evacuating the engine room

Answer

dumping fuel oil

Question 21

What is meant by the term emergency bilge suction?

Accepted Answer

The means by which the machinery space bilge is pumped out by a pump not normally used as a bilge pump and drawing a suction directly on the bilge independent of any bilge manifolds or automatic bilge suction valves.

Answer

The means by which the machinery space bilge is pumped out by a pump not normally used as a bilge pump and drawing a suction on the bilge through either bilge manifolds or automatic bilge suction valves.

Answer

The means by which the machinery space bilge is pumped out by a pump normally used as a bilge pump and drawing a suction directly on the bilge independent of any bilge manifolds or automatic bilge suction valves.

Answer

The means by which the machinery space bilge is pumped out by a pump normally used as a bilge pump and drawing a suction on the bilge through either bilge manifolds or automatic bilge suction valves.

Question 22

Which of the following compressors would be used for a dead ship start-up of a ship's service diesel- generator on a motor ship?

Accepted Answer

Emergency air compressor

Answer

Topping air compressor

Answer

Ship's service air compressor

Answer

Starting air compressor

Question 23

Which of the following statements represents the proper criteria to decide when to drain a filter/moisture separator as used in a ship's service air system hose station?

Accepted Answer

The bowl should be drained before the moisture level reaches the lower baffle.

Answer

The bowl should be drained daily with no need to check the moisture level.

Answer

The bowl should be drained whenever moisture droplets appear in the bowl.

Answer

The bowl should be drained after the bowl completely fills with moisture.

Question 24

Figure "B" shows a block diagram of a central operating system configured for supervisory control. What is the function of the block labeled "ANALOG (A-D MUX)"?

Accepted Answer

A high-speed solid-state switching device called a multiplexer capable of scanning a large number of analog sensors in a short period of time and converting these signals to digital values for processing by the CPU.

Answer

A low-speed solid-state switching device called a multiplexer capable of scanning a small number of analog sensors in a long period of time and converting these signals to digital values for processing by the CPU.

Answer

A high-speed solid-state switching device called a multiplexer capable of scanning a large number of digital sensors in a short period of time and converting these signals to analog values for processing by the CPU.

Answer

A low-speed solid-state switching device called a multiplexer capable of scanning a small number of digital sensors in a long period of time and converting these signals to analog values for processing by the CPU.

Question 25

In a closed-loop process control system, what statement concerning feedback is true as it relates to stability and the direction of error displacement?

Accepted Answer

Negative feedback is used to minimize instability by pushing the system in the opposite direction as the error displacement.

Answer

Negative feedback is used to minimize instability by pushing the system in the same direction as the error displacement.

Answer

Positive feedback is used to minimize instability by pushing the system in the same direction as the error displacement.

Answer

Positive feedback is used to minimize instability by pushing the system in the opposite direction as the error displacement.

Question 26

In a series circuit, what is the applied voltage (or sum of the applied voltages) equal to?

Accepted Answer

the sum of the individual voltage drops

Answer

the total resistance divided by the total current

Answer

the sum of the individual currents multiplied by the number of resistors

Answer

the total current divided by the total resistance

Question 27

In figure "A", with the switch closed, if "R1" and "R2" have unequal resistance values, what statement is TRUE?

Accepted Answer

The current flow through "R1" will differ from the current flow through "R2".

Answer

The energy dissipated in "R1" will be the same as the energy dissipated in "R2".

Answer

The current flow through "R1" will equal the current flow through "R2".

Answer

The voltage drop across "R1" will not be equal to the voltage drop across "R2".

Question 28

In a simple DC circuit consisting of one resistive load, the resistance is held constant while the applied voltage is halved. What will be the effect on the current flow as compared to the original current?

Accepted Answer

be divided by two

Answer

double

Answer

remain the same

Answer

be divided by four

Question 29

Which statement is TRUE regarding figure "6" of the illustration? Illustration EL-0026 EL-0026.jpg

Accepted Answer

The symbol represents a switch using maintained contact with "either/or" logic.

Answer

The symbol represents an overload relay.

Answer

The symbol represents a switch which functions with analog parameters.

Answer

The symbol represents a computer cable pin plug.

Question 30

Of the images in figures "A" through "D", which represents the schematic symbol shown in Figure "2"?

Accepted Answer

Figure "B"

Answer

Figure "A"

Answer

Figure "C"

Answer

Figure "D"

DDE – Unlimited HP Practice Test

What is on the DDE – Unlimited HP exam

Motor Plants

Steam Plants

Gas Turbine Plants

Engineering Safety & Environmental Protection

General Subjects

Electrical - Electronic - Control Engineering

DDE – Unlimited HP exam FAQ

Q How many questions are on the DDE – Unlimited HP exam?

Q What modules are on the DDE – Unlimited HP exam?

Q What score do I need to pass the DDE – Unlimited HP exam?

Q Are these the real questions?

Q Can I take a timed DDE – Unlimited HP practice exam?

Other engine practice tests

Ready to pass the DDE – Unlimited HP exam?

Module	Questions	Illustrations	Practice
Q620 Motor Plants	70	30	Practice →
Q621 Steam Plants	70	4	Practice →
Q622 Gas Turbine Plants	70	7	Practice →
Q623 Engineering Safety & Environmental Protection	70	3	Practice →
Q624 General Subjects	70	20	Practice →
Q625 Electrical - Electronic - Control Engineering	70	20	Practice →
Total	420	84