VTS Meteorology and Environmental Factors 2 — Questions and Answers
Question 1: What hydrodynamic phenomenon causes a vessel to sink deeper into the water when transiting shallow channels at speed, reducing available under-keel clearance?
- Heel
- Squat (Correct answer)
- List
- Trim
Correct answer: Squat
Squat is a hydrodynamic effect where a vessel moving through shallow water experiences reduced pressure under the hull, causing it to settle lower and potentially reducing under-keel clearance to dangerous levels.
Question 2: A temperature inversion exists over the harbor. How does this atmospheric condition most likely affect VHF radio communications used by VTS?
- It reduces VHF range due to increased atmospheric absorption
- It can cause ducting, extending VHF range well beyond normal line-of-sight limits (Correct answer)
- It has no measurable effect on VHF radio propagation
- It causes selective interference only on DSC channel 70
Correct answer: It can cause ducting, extending VHF range well beyond normal line-of-sight limits
A temperature inversion creates a boundary layer where warmer air overlies cooler air, which can trap and refract VHF radio waves, causing 'ducting' that extends usable range far beyond normal line-of-sight.
Question 3: What is 'significant wave height' as reported in marine weather forecasts provided to VTS operators?
- The maximum wave height recorded in a 24-hour observation period
- The average height of the highest one-third of all waves in a given period (Correct answer)
- The height of the single largest wave observed during the period
- The wave height exceeded by exactly 50 percent of all waves
Correct answer: The average height of the highest one-third of all waves in a given period
Significant wave height is the average of the highest one-third of all waves in a measurement period, and it closely corresponds to what a trained mariner would visually estimate as the prevailing wave height.
Question 4: When tidal current through a harbor entrance exceeds 4 knots, what action would a VTS operator typically recommend or require for a large inbound vessel?
- Immediate anchoring in the fairway to await calmer conditions
- Delaying vessel transit until the current decreases to a manageable level (Correct answer)
- Increasing vessel speed to overcome the adverse current
- Switching to hand steering and reducing radar range
Correct answer: Delaying vessel transit until the current decreases to a manageable level
Strong tidal currents severely reduce a vessel's maneuverability and steering response; VTS operators advise delaying transit until the current slackens, as timing a passage around slack water is standard maritime practice.
Question 5: What is a 'storm surge' and why must VTS operators account for it in their traffic management decisions?
- A sudden increase in vessel traffic attempting to reach port before a storm arrives
- A wind-driven and low-pressure-induced rise in sea level that affects actual water depths and port flooding risk (Correct answer)
- The turbulent wake generated by large vessels departing during a storm
- A rapid intensification of wind speed during the passage of a squall line
Correct answer: A wind-driven and low-pressure-induced rise in sea level that affects actual water depths and port flooding risk
A storm surge is an abnormal rise in sea level caused by strong onshore winds and low atmospheric pressure; it changes actual under-keel clearances, can cause dock flooding, and affects the safety of vessels already moored.
Question 6: How should a VTS operator adjust traffic management when a dense fog advisory is in effect across the port service area?
- Increase vessel speed requirements to clear the port approach faster
- Implement reduced speed advisories and increase minimum separation distances between vessels (Correct answer)
- Suspend all VHF communications until visibility improves above 2 miles
- Transfer all navigational responsibility solely to individual vessel masters
Correct answer: Implement reduced speed advisories and increase minimum separation distances between vessels
In restricted visibility, VTS implements enhanced traffic management including reduced speed advisories and increased vessel separation to provide additional stopping distance and reaction time, reducing collision risk.
Question 7: What is 'ice accretion' and what specific navigation hazard does it present to vessels monitored by VTS in winter conditions?
- Build-up of ice on the vessel's superstructure causing stability loss due to increased topside weight (Correct answer)
- Formation of ice crystals in fuel lines reducing available engine power
- Ice deposits on VHF antennas causing communications to fail
- Gradual freezing of the harbor approach channel reducing available depth
Correct answer: Build-up of ice on the vessel's superstructure causing stability loss due to increased topside weight
Ice accretion on superstructure, decks, and rigging adds significant weight high above the waterline, raising the vessel's center of gravity and reducing metacentric height, which can lead to capsizing.
VTS Meteorology and Environmental Factors 2
What hydrodynamic phenomenon causes a vessel to sink deeper into the water when transiting shallow channels at speed, reducing available under-keel clearance?