The prime reason for which every seafarer is wished
“Smooth sailing and Calm seas” before boarding a vessel is to keep them
safe from storms.
Rough weather situation has been faced at least once or
more by every seafarer during the course of his/her career. Some of the
most common forms of heavy or rough weather are
tropical depressions or storms, typhoons, cyclones, hurricanes etc, generated due to varying atmospheric pressures over different parts of the earth.
Beaufort wind scale criteria
classifies strong winds as near gale, gale, strong gale, storm, violent
storm and hurricane based on ascending magnitude of wind force.
Movement of sun causes pressure belts to shift and thus varying
temperatures over land masses and water bodies causes pressure
differences.
Tropical depressions occur often in middle latitudes and
tropical cyclones that originate in the Inter Tropical Convergence Zone.
A depression may often develop and travel in any direction whereas
tropical storms are mostly found to follow predicted path* in both the
hemispheres.
Tropical storms recurve after following a particular
track*. It is therefore very important for a mariner to predict the
location, magnitude and path of the storm, which are required to avoid
these regions or navigate with caution while in navigating these areas.
Following are a few precautions which seafarers must follow while
encountering tropical storms or navigating in areas of their frequent occurrence.
Use Available Information: Tropical
storms and depressions are formed by pressure and temperature
variations. A mariner has access to information regarding seasonal areas
and frequency of occurrence through Maritime Safety information via
EGC, Admiralty Sailing Directions, Ocean passages of the world and
several other means. Thus if prior information is available regarding
the legs of a voyage where rough weather is expected a sheltered passage
or alternate route can be carefully planned to divert the vessel timely
when required.
Study Weather Report: Often weather
report and weather fax give warnings well in advance about unsettled
weather conditions. Thus a careful selection of Nav Areas and type of
weather reports by the navigating officer can be instrumental in
obtaining early warning about a storm. Frequent observations from
various meteorological instruments and prevailing weather onboard can be
used to confirm weather reports.
Keep Away From Centre of Storm: Once
presence of a storm or depression is confirmed. It is vital to establish
distance of the vessel from it, location of the eye of the storm,
centre of the depression, and storm’s track and path. Buoy Ballot’s law
states – Face the wind and centre of low pressure will be from 90
degrees to 135 degrees on your right hand in N hemisphere and on your
left hand in S hemisphere. It is advisable to keep at least 250 miles
away from the centre of a storm however some companies prescribe
specific distances in their Safety Management Manuals.
Check Stability Of The Vessel: A prudent
check is required on the stability condition of the vessel and its
compliance with intact stability criteria. Damage stability conditions
to be evaluated carefully before beginning of a voyage as it will assure
compliance with damage stability requirements. A vessel can thus take
heavy weather ballast while or before proceeding to rough weather areas.
Heavy weather ballast provides additional stability to the vessel and
by lowering the centre of gravity makes vessel more stable as the GM*
increases. Heavy weather ballast tanks are designated onboard vessels
and if those tanks carried oil previously they must be crude oil washed
before carrying heavy weather ballast in them.
se Ballast Tanks To Minimise Free Surface Effect:
As a part of good seamanship all the ballast tanks which are slack can
be pressed up to minimise the free surface effect which will also help
to increase the GM. Well planned stowage of cargo , ballast or both can
minimise the number of slack or partly filled tanks.
Be Careful While Changing Speed, Angle, and Direction:
Often waves associated with a storm or depression causes reduction in
intact stability of vessel with a threat of capsizing or rolling of
vessel to very large angles. IMO circular MSC 1228 provides guidelines
with respect to careful reduction of speed, changing the angle and
direction of encounter and adjusting encounter period of waves to avoid
parametric or synchronous rolling motions.
Secure Loose Equipment/Cargo on Deck: For vessels with lesser freeboard, decks are washed frequently by seas with greater magnitudes. Thus
securing of various loose equipment on
deck, additional lashings to be taken to strengthen and prevent their
loss being washed away into the sea. Safety lifelines can be rigged on
vessels carrying cargoes on deck. Additional lashing must be taken to
secure anchors, lifeboats, lifebuoys and liferafts.
Secure Weather and Water Tight Openings: Various
weather tight and water tight openings like side scuttles, hatch
covers, portholes, doors, manholes to be securely closed to prevent any
ingress of water. Leaking, damaged gaskets or inadequate securing for
covers of such openings may affect the integrity of compartment they are
protecting. Alarms and indicators for closing of remote watertight
doors and openings are provided on Navigation bridge, their operational
state to be confirmed prior beginning of the voyage.
Secure Doors Forward Of Collision Bulkhead: Special
emphasis to be provided to secure the doors and openings forward of the
collision bulkhead for e.g. forepeak store and hatches, vents and
openings forward. These spaces often house forward mooring equipment and
associated electrical or hydraulic machinery. Spurling pipe covers need
to be cemented well in advance. Bilge alarms in such remote
compartments should be tried out regularly to give an early warning of
any ingress of water or flooding. Any openings in subdivisions of
watertight compartments which can cause progressive flooding must be
secured.
Drains and Scuppers Must Be Free: All drains on deck and scuppers for drainage of water must be free to prevent any accumulation of water on deck.
Secure Aerials and Antennas: Antennas,
aerials, stay wire clamps and lashing to be inspected before the wind
speed picks up. Winds of gale force and above can easily break and blow
away aerials. Storms are associated with lightning and thundering thus
all aerials and antennas to be earthed and any low insulation alarms to
be investigated carefully.
Keep Check on RPM To Avoid Load Fluctuation on Main Engine: Due to unsettled movement of vessel often
load fluctuations on the main engine are observed. A careful setting of RPM can help to keep the fluctuations on the main engine within permissible limits.
Inform All Departments: All the
departments deck, engine and galley should be informed well in advance
of any storm warning so that all the deck, engine and galley stores,
hospitals, sick bays and work areas are lashed and secured. Any major
overhaul jobs, working aloft or lifting of heavy machinery on deck and
engine room using overhead or deck crane can be postponed or avoided.
Morale of the Crew To Be Kept High: The
morale of the crew should be kept high as often heavy rolling and
pitching causes giddiness, nausea and reduced appetite amongst crew
members.
*Track : A curve formed by previous known positions of a storm centre.
*Path : A curve formed based on predicted positions of a storm centre.
*GM : Its the vertical distance between Centre of Gravity and the Metacentre.