Question associated with FOG

Question 1

(Explain) Dew point temperature

Answer 1

The Dew Point temperature is the temperature at which a particular sample of air becomes saturated

Question 2

(Explain) Relative Humidity

Answer 2

Relative Humidity is the ratio of water vapor present in unit volume of air to the quantity required to saturate it at the same temperature, expressed as a percentage

Question 3

Outline the Process of Formation of ADVECTION FOG (Sea Fog)

Answer 3

Advection fog occurs when air moves over a surface that is at a lower temperature than its dew point. The air at the surface is cooled by conduction below its dew point and condensation occurs.

Question 4

Outline the Process of Formation of Radiation FOG (Land Fog)

Answer 4

Radiation fog usually forms at night over land.
it is Anticyclonic conditions.
Low cloud cover.
High outgoing radiation.
Radiation reduces the surface temperature.
The air in contact with the surface is cooled by conduction below its dew point and condensation occurs.

Question 5

Outline the Process of Formation of SEA SMOKE (Frost Smoke).

Answer 5

Sea smoke
Cold air flowing over warm water may become saturated close to the surface by evaporation from the
water

Question 6

Outline how the OOW can use on board observations to predict the time when a vessel will encounter Advection fog at sea.

Answer 6

Regular observations of the dew point temperature of the air and sea surface temperature are taken.
A graph is constructed of these against time.
When no fog is present the sea surface temperature is greater than the dew point temperature of the air.
Converging temperatures, typically a decreasing sea surface temperature with little change in the dew
point temperature, indicate an increasing probability of fog. The tendencies can be projected and fog is probable when the sea surface temperature is lower than the
dew point temperature of the air.

Question 7

State THREE ocean areas of the world where sea/advection fog may commonly be encountered.

Answer 7

Any area where humid air is adjacent to a sea surface with a lower temperature than the dew point
temperature of the air.
The Grand Banks off Newfoundland in the North West Atlantic Ocean over the Labrador Current.
The Eastern Atlantic over the Canaries current.
The North West Pacific Ocean over the Kamchatka current.
The Eastern Pacific Ocean over the California current.
The Eastern South Atlantic over the Benguela current.
The Eastern South Pacific Ocean over the Peru Current

Question 8

Write a section of Master’s Standing orders outlining the procedure to be adopted on
encountering restricted visibility.

Answer 8

Call the Master.
Post lookout/s.
Engage hand steering.
Inform Engine Room.
Engines to standby.
Reduce to a safe speed.
Comply with appropriate COLREGS.
Commence sound signals.
Check ARPA function / commence radar plotting.
Monitor visibility by sighting ranges of vessels / objects.
Monitor sea surface and dew point temperatures.