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E-NAV > Exam 1 > Flashcards

Exam 1 Flashcards

1
Q

Doppler speed log

A

registers a change in frequency between the transmitted signal and the received signal and then calculates the velocity of the vessel based on the frequency shift

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2
Q

Echo sounding is a type of?

A

Sound Navigation and Ranging (SONAR)

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3
Q

Echo sounding is used to?

A

determine the depth of the water by transmitting sound pulses into water

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4
Q

Fathometer indicates the depth of water where?

A

under keel or where the transducer is located

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5
Q

Fathometer is dependent on both?

A

specular (direct) and diffuse (reflection at an angle) reflection

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6
Q

Range of fathometer is?

A

0 to 4,500 feet

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7
Q

Fathometers emit how many pulses per minute?

A

10 to 600 pulses per minute

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8
Q

Speed of sound through water is approximately?

A

4,800 feet per second

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9
Q

You should always know your _________s location.

A

Fathometer

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10
Q

What does a Oscillator do?

A

creates electrical signal at the desired frequency

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11
Q

What does a Transducer do?

A

converts electrical signal into ultrasonic vibrations for transmission. Also converts the return echo back into an electrical signal

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12
Q

Name two types of Transducers?

A

Electrostrictive and Magnetostrictive

types

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13
Q

It is essential the user select the _____ depth soundings on the depth sounder as the navigational chart in use.

A

SAME

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14
Q

Gain: the ____ the bottom, the less gain (sensitivity) required

A

harder

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15
Q

Define Bathymetric Navigation?

A

The method of navigating by using a fathometer

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16
Q

Speed Log is used to determine the vessels _____.

A

Velocity

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17
Q

Name three different Speed Logs?

A
  1. Patent logs: Small tubular finned device attached to the end of the drag line that would spin as the vessel moved through the water
  2. Pitot-static (pitometerlog): based on principle of comparative measurements between static and dynamic pressured in a pilot tube extending from a vessel’s hull
  3. Impeller log: electromagnetic device which used a small propeller spun by water which was then converted to an electrical signal
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18
Q

Modern Speed Logs are?

A

Electromagnetic or doppler

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19
Q

Define the Doppler Speed Log, Doppler Effect:

A

Shift in frequency between a transmitted and received signal caused by the motion of a vessel over bottom or through water

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20
Q

The Doppler Speed Log receives what through the water?

A

reflected signal from particles suspended in water.

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21
Q

True or False: The Doppler Speed Log registers change in frequency, not time, to measure speed

A

True

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22
Q

The speed of sound through ocean water is nearly always __________.

A

faster than the speed of calibration for the fathometer

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23
Q

Which factor has the greatest effect on the amount of gain required to obtain a fathometer reading?

A

Type of bottom

24
Q

If a sound signal is emitted from the oscillator of a fathometer, and two seconds elapse before the returning signal is picked up, what depth of water is indicated?

A

824 fathoms

25
Q

When operated over a muddy bottom, a fathometer may indicate __________.

A

two depth readings

26
Q

The recording fathometer produces a graphic record of the __________.

A

depth underneath the keel against a time base

27
Q

What should you apply to a fathometer reading to determine the depth of water?

A

Add the draft of the vessel.

28
Q

When using an echo sounder in deep water, it is NOT unusual to __________.

A

receive a strong return at about 200 fathoms (366 meters) during the day, and one nearer the surface at night

29
Q

All echo-sounders can measure the __________.

A

actual depth of water below keel

30
Q

The speed of sound in water is approximately __________.

A

4.5 times its speed in air

31
Q

A Doppler speed log indicates speed over ground __________.

A

in the bottom return mode

32
Q

A Doppler speed log indicates speed through the water __________.

A

in the volume reverberation mode

33
Q

What will NOT induce errors into a Doppler sonar log?

A

Increased draft

34
Q

A Doppler log in the volume reverberation mode indicates __________.

A

speed through the water

35
Q

A Doppler log in the bottom return mode indicates the __________.

A

speed over the ground

36
Q

Velocity of sound through water to calculate depth of water?

A

(Depth = R * T)

37
Q

The assumed speed of sound through water is approximately ______ feet per second or _____ greater than the speed of sound through air

A

4800, 4.5

38
Q

Radar is an acronym for?

A

radio detecting and ranging

39
Q

First commercial application on US merchant vessels occurred in the late _____.

A

1940’s

40
Q

Define the Fundamentals of RADAR?

A

A transceiver sends a pulse modulated signal out, measures the time until the signal’s return, determines distance from this, and can display the returns in a directionally accurate presentation because of the use of a directional antenna

41
Q

Radar waves are emitted on two different frequencies, what are they?

A
  1. X Band operates at 9,375 MHz with a wavelength of 3.2 centimeters
  2. S Band operates at 3,070 MHz with a wavelength of 10 centimeters
42
Q

Define Superrefraction?

A

Superrefraction: increases downward bending of radar waves and therefore increases the ranges at which targets may be detected

43
Q

Define Subrefraction?

A

Subrefraction: radar waves bend upward, thus the range at which targets can be detected is reduced

44
Q

Define Ducting?

A

Ducting: extreme cases of superrefraction.

45
Q

Sea Return is minimized by adjusting what?

A

RF GAIN or SEA CLUTTER CONTROL

46
Q

Name the _____ interferences?

A

8

47
Q

What are the different Radar interference’s?

A 
Rain Clutter
Indirect or false echoes
Multiple Echoes
Second-Trace Echoes
Side Lobe Effects
Electronic Interference
Overhead Cable Effect
Spoking (Equipment Failure)
48
Q

True or False: Spoking is a Equipment Failure, Occurs when there is a modulator problem and indicated by many radial lines showing up on the radar screen

A

TRUE

49
Q

The Fundamentals of RADAR!!!!!, THREE FACTS:

A

Uses basic time-rate-distance computations
Known speed of radar waves and time it takes for an echo to return
Radar waves travel at the speed of light

50
Q

Watch Condition A?

A

One Deck Officer: Open Waters Clear Visibility

51
Q

Watch Condition B?

A

Two Deck Officers: Entering or Leaving a Port Without the Pilot onboard

52
Q

Watch Condition C?

A

Three Deck Officers: Situation where increased navigational assistance is needed, reduced visibility, higher traffic.

53
Q

Watch Condition D?

A

Local Pilot Embarked

54
Q

RULE 5

A

Look-Out

55
Q

RULE 6

A

Safe Speed

56
Q

RULE 7

A

Risk of Collision

57
Q

Describe a Fathometer?

A

Determines depth of water by generating sonic pulses that are directed towards the ocean floor

The sonic pulses are reflected off the ocean floor and return to the transducer

E-NAV (1 decks)

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