VTS Navigation Systems 5 — Questions and Answers
Question 1: What is the purpose of a Vessel Traffic Service (VTS) radar's 'gain' control?
- To adjust the sensitivity of the radar receiver to detect weaker targets (Correct answer)
- To change the rotation speed of the radar antenna
- To filter out AIS-correlated targets
- To zoom in on a specific area of the radar display
Correct answer: To adjust the sensitivity of the radar receiver to detect weaker targets
Radar gain controls receiver sensitivity; increasing gain detects weaker or more distant targets, while reducing gain can eliminate noise and clutter.
Question 2: A vessel's AIS is transmitting a static draught of 8 meters, but the navigable channel has a controlling depth of 9 meters. What action should the VTS operator take?
- Monitor the vessel and verify the charted controlling depth against current tidal conditions before advising (Correct answer)
- Immediately prohibit the vessel's transit
- Accept the data as safe without further action since there is 1 meter clearance
- Alert the vessel that it is too deep to enter
Correct answer: Monitor the vessel and verify the charted controlling depth against current tidal conditions before advising
The operator must account for tidal state to determine actual underkeel clearance before determining whether the transit is safe and what advice to provide.
Question 3: What is 'sea clutter' on a radar display, and which control is used to reduce it?
- Returns from waves near the vessel, reduced using the STC (Sensitivity Time Control) or sea clutter control (Correct answer)
- Interference from other radar systems, reduced using the interference rejection filter
- False echoes from land, reduced by adjusting radar gain
- Multipath reflections, reduced by decreasing pulse length
Correct answer: Returns from waves near the vessel, reduced using the STC (Sensitivity Time Control) or sea clutter control
Sea clutter is caused by radar energy reflecting off wave surfaces close to the antenna, and the STC control progressively reduces gain at short ranges to suppress it.
Question 4: Under 33 CFR Part 161, which vessels are generally required to participate in a U.S. Vessel Traffic Service?
- Power-driven vessels of 40 meters or more in length, certain towing vessels, and vessels carrying hazardous cargo (Correct answer)
- All vessels over 20 gross tons
- Commercial fishing vessels over 100 tons
- All vessels regardless of size when inside the VTS area
Correct answer: Power-driven vessels of 40 meters or more in length, certain towing vessels, and vessels carrying hazardous cargo
33 CFR Part 161 specifies that VTS participation is mandatory for power-driven vessels ≥40 meters, certain towing vessels, and vessels carrying hazardous materials in designated VTS areas.
Question 5: What is the function of a 'waypoint' in electronic navigation systems used by vessels reporting to VTS?
- A predetermined geographic position used as a reference point along a planned route (Correct answer)
- A VTS-assigned holding position outside the port
- The point where a vessel must report its position by radio
- An anchor area designated on an electronic chart
Correct answer: A predetermined geographic position used as a reference point along a planned route
A waypoint is a specific latitude/longitude position programmed into a navigation system to define the intended route, allowing automatic course guidance.
Question 6: How does AIS Class A differ from AIS Class B in reporting interval during transit at speed?
- Class A reports every 2–10 seconds depending on speed; Class B reports every 30 seconds (Correct answer)
- Class A reports every 30 seconds; Class B reports every 2 seconds
- Both classes report at the same interval regardless of speed
- Class A only reports when requested by VTS; Class B is continuous
Correct answer: Class A reports every 2–10 seconds depending on speed; Class B reports every 30 seconds
Class A AIS (fitted on SOLAS vessels) reports position every 2–10 seconds when underway at speed, while Class B (recreational/smaller vessels) reports every 30 seconds.
Question 7: What navigational hazard does a 'squat effect' present to a vessel transiting a shallow or confined channel, and why must VTS operators be aware of it?
- Squat causes a vessel to sink lower in the water at speed, reducing underkeel clearance and increasing grounding risk (Correct answer)
- Squat causes radar returns to become distorted and harder to track
- Squat shifts a vessel's center of gravity, making it list to one side
- Squat creates a pressure wave that pushes smaller vessels away
Correct answer: Squat causes a vessel to sink lower in the water at speed, reducing underkeel clearance and increasing grounding risk
Squat effect occurs when a vessel's speed through shallow water causes it to sink lower than its static draught, potentially grounding even if static calculations show adequate clearance.
VTS Navigation Systems 5
What is the purpose of a Vessel Traffic Service (VTS) radar's 'gain' control?