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ENAV > Test 2 > Flashcards

Test 2 Flashcards

1
Q

How do radars operate in relative motion?

A

Own ship is shown as a fixed point and everything is relative to your own ship

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2
Q

What do you use to determine if a close quarters situation is developing?

A

Proximity and time

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3
Q

What info does gps give you?

A

Continuous positioning and timing info, anywhere in the world under any weather conditions

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4
Q

How many satellites are required for a fix?

A

4

Constellation of 24 operational satellites

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5
Q

GPS is operated by the government, so

A

It can be suspended

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6
Q

What contributes to gps error?

A

Errors originating at satellites, receiver, and signal propagation (atmospheric refraction)

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7
Q

Ephemeris error

A

Difference between expected and actual orbit of a FPS satellite

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8
Q

Receiver errors

A

Clock errors, multi path error, receiver noise, and antenna phase variations

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9
Q

Signal propagation errors

A

Delays of gps signal as it passes through the ionosphere and tropospheric layers

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10
Q

ARPA provides range and bearing

A

Immediately

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11
Q

ARPA provides relative motion with 95% accuracy and cpa/tcpa within

A

1 minute

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12
Q

ARPA provides true motion with 95% accuracy and true course and speed within

A

3 minutes

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13
Q

According to cfr 33, required accuracy of ARPA is

A

. 5 miles

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14
Q

Relative vectors give you

A

Instant assessment of collision risk

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15
Q

True vectors give you

A

Representation of aspect and which rules apply

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16
Q

Parallel indexing is

A

Used as a measure to monitor progress of a vessel on track line, minimize cross track difference, and keep safe distance to shore

17
Q

Benefits of ECDIS

A

Reduced workload
Displays ships position in real time
Central role at steering station
Situation dependent display

18
Q

ECDIS benefits continued

A 
Radar overlay
Auto route monitoring 
Auto track control
Assistance in special maneuvers 
Up to date info
19
Q

ECDIS risks

A 
System characteristics 
Hardware failure 
System reliability 
Error free software 
Inaccurate chart data
Incorrect position determination 
Over-reliance 
Improper settings
User related short comings
20
Q

LT Cortesia

A

Grounded on varne bank in English Channel in 2008 because insufficient knowledge of ECDIS
Maladjustment of safety contours
Defaulted to 30 meters

21
Q

CSL Thames

A 
Grounded in sound of mull 2011
3rd mate altered course for another vessel and went to shallow water
Alarm was inoperative 
Incorrect safety contour of 10m
Draft was 10.63m
22
Q

Is ECDIS required by rule 5?

A

No, because you have other means

23
Q

Safety depth

A

Ships draft plus squat

24
Q

Safety contour

A

Division between safe and unsafe water

Draft + squat + UKC - ht of tide

25
Q

Deep contour

A

Area where depth is such that own ship may experience squat

Twice draft

26
Q

Shallow contour

A

Highlight gradient of seabed adjacent to safety contour

Next shallower than safety contour

27
Q

Two leading causes of ECDIS incidents

A

Operator error

Lack of training

28
Q

Effeyrange of AIS

A

20 miles

29
Q

What static AIS info?

A 
Every 6 minutes:
IMO #
Name and call sign
Length and beam
Ship type
Demensions
Location of fixing antenna
Type of positioning equipment 
Destination 
ETA
30
Q

What dynamic AIS info?

A 
2-10 seconds:
MMSI
nav status
Rate of turn
Position coordinates 
Course over ground 
Heading
Bearing at own position 
UTC seconds
31
Q

Advantages of AIS

A

Longer range detection
Real time computation
No risk of target swap
No target loss in clutter

32
Q

Disadvantages of AIS

A

Complacency
Accuracy is only as good as what was inputed
Not all ships have

33
Q

Radar most accurate determination

A

Bearing

34
Q

What is dilution of precession?

A

Happens when gps satellites are close together
Best when one overhead and others equally spaced across the horizon
Higher dilution equals more position error

35
Q

What is target swap?

A

Multiple vessels close proximity to each other and same bearing from own vessel

36
Q

Identity and explain the basic theory of gps

A

1) . Space segment consists of satellites that transmit radio signal at speed of light which contain a navigation message (location and time)
2) . User segment consists of receiver which receives space segment transmission. Transmission is processed and position of receiver is calculated.
3) . User segment does not transmit a signal
4) . Control segment of god system consists of worldwide network of tracking stations, with a master control station in Colorado Springs. Tracks satellites to determine locations.
5) . 4 satellites must be visible to provide info

37
Q

Explain dgps operation

A

1) . Supplements and/or enhances gps
2) . Reference stations provide corrections to gps signals
3) . Each ref station has a gps receiving system and gps position of reference station is computed and compared to its actual position
4) . The differential info or error in fix position is transmitted to receivers used in the geographical area near the ref station
5) . Dgps optimum range of 150 miles

38
Q

Describe operation of AIS

A

1) . Continuously transmits and receive info on maritime vhf (25 or 12.5 kHz)
2) . Transmissions fit into a time slot and stations synchronize themselves to other stations to avoid overlap of slot transmissions
3) . Range is line of sight
4) . Transmits static, dynamic, and voyage info
5) . Changes in heading and course are immediately apparent

39
Q

Why is parallel indexing used

A

1). Measure to monitor progress of a vessel on the track and minimize cross track distance
2). Bearing line drawn parallel to original course with a known fixed perpendicular distance between both the lines is used as a reference
3). Increase or decrease of perpendicular distance between the bearing lines drawn parallel to course line and ships position any time will indicate cross track deviation
Parallel indexing is frequently used in areas where coastlines are rocky and provide strong Radar returns

ENAV (2 decks)

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