What are air masses
Extremely large bodies of air whose properties of temp & humidity are similar in any horizontal direction
What is a frontal system
A transitional zone between two air masses of different densities most often caused by temperature differences i.e. cold air mass following a warm air mass
Warm Front
When warm air replaces cold air on passage the cold denser air forces the warm air upwards where it converges and results in cloud formation
As it converges it becomes unstable forming Nimbostratus cloud
Conditions associated with a warm front
Always rain in front of the front wind increasing on approach and steady during passing
The wind veers
Restricted vis
Cold front
Cold air replacing warm air on passage forcing up the warm air and creating a much steeper front forming cumulonimbus cloud
The cold unstable air draws in warmer air while the very cold air subsides quickly creating static
Conditions associated with a cold front
Wind increases and veers
Heavy rain storms and possible thunderstorms
Temperature decrease
Moderate to good vis
Occlusion
cold front following a warm front
As the cold air moves quicker the cold front catches the warm front and creates an occlusion
What is a TRS
An intense area of low pressure, force 12 or higher that occurs in the tropical or suntropics
Describe the formation of a TRS
- In a warm region (27°C sea temp) the air above is heated and rises
- Cooler air moves in to replace the rising air which is subsequently heated while carrying moisture
- The process repeats until you end up with a core that’s at least 15° higher than the surroundings
- The Coriolis creates a cyclonic rotation around the eye
When does a TRS occur
Late summer
Northern Hemisphere : Jul-Oct
Southern Hemisphere: Dec - Mar
What is the dangerous semi circle
How do you know your in it?
This is the half of the storm where the wind is pushing you towards the path or centre of the storm
In the dangerous semicircle in the northern Hemisphere the wind will be veering and pressure decreasing
What is the navigable semicircle?
How do you know youre in it?
This is the half of the storm where the wind is pushing you away from the path or centre
In the northern Hemisphere the wind will be backing and pressure decreasing
What to do if you’re in the dangerous semicircle
In the northern Hemisphere wut wind 4 points on starboard bow and head out
In the southern hemisphere put wind 4 points on port bow and head out
What to do in the navigable semi circle
If in the northern Hemisphere put the wind 4 points on the starboard quarter and head out
I’m the southern hemisphere put her wind 4 points on the port quarter and head out
What to do if the wind direction is steady and pressure decreasing
You are in the path so turn to the navigable semicircle then put the wind 4 points on the starboard or port quarter
If heading North and the wind is constant in the northern Hemisphere
Turn around and get to the navigable semicircle
What are the signs a TRS is approaching
Decrease in pressure and diurnal variation masked
Swell increasing and easterly
Sky becomes ugly and threatening
Colouring in sky (bright reds and oranges)
Increase in wind
What are the duties of the master on sighting a TRS
Report by all available means (pan pan) to ships in the vicinity and nearest shore station including the position, pressure tendancy wind sea state and swell, time and date (UTC) along with the course and speed of the ship and follow up with subsequent reports hourly
Describe the formation of Ice
Cold temps causing sea water to freeze at about -2°C
The brine becomes trapped in small pockets
After time the salt gradually drains out through channels causing the ice to become harder
After a year all salt is lost and it becomes full formed FW ice
Ice detection
Extra lookouts
Ice radar
EGC, Nav tax, ice patrol and satellite imagery (NOAA)
Listening watch (ice breaking off produces a thunderous roar)
Reflection of moonlight
In fog reflection of sunlight or if no sun appears as a dark mass
Walruses, seals and birds
Ice blink - a yellowish glare on the clouds
Monitor sea temp in the Atlantic for cold currents that could carry ice
Abrupt smoothening of the sea
Precautions for Navigating in / Transiting through Ice
Monitor nav warnings / EGC
Set up radar / Ice radar
Extra lookouts
Safety - PPE / Grit decks
Drain fire main / remove portable extinguishers
Consider FW in Lifeboat (stow in accessible location)
Cover Winches / hydraulics - remove lashings and ropes from main deck
Monitor cargo holds
Consider stability (ice accretion)
Monitor ballast line
Monitor SW cooling for engines
What are your concerns with heavy weather
Safety of the ship
Damage to the vessel
Cargo shift, loss or damage
Propeller immersion
Ship Type / handling
Parametric rolling
Heavy weather precautions
Assess and tighten cargo lashings as per the CSM
Assess stability, ensure positive, minimize Free Surface effect and consider ballasting the head
Anchors additional lashings and hawse pipes covered
Inform ER and galley
Secure all moveable objects
Close deadlights
Check lifeboat lashings
Consider safe access, safety ropes and guidelines
Follow SMS and checklists
What is parametric rolling and when does it occur
A dangerous rolling motion that occurs when the wavelength is nearly equal to the ships length and when the roll period is 2 x the wave encounter
It occurs in following / quartering or head seas on vessels which have fine bows together with a fuller stern
