Background
The Navigator possesses 2 personal traits that greatly
enhance his ability to navigate. His eyes and his ears. Both require he or she
have the highest medical standards for sight and hearing. Colour blindness is
not an option if you are to be a deck officer as you must be able to
distinguish between the major navigational colours of red, green and white.
The navigator is trained to identify conditions in his maritime
environment. The sky, the horizon, sea surface and objects around him, all need
to be analysed and translated into navigational decisions. He must be able to
differentiate them by day or by night.
By day
During the day he normally has a focus on weather.
To start interpreting weather for navigation purposes, the navigator first turns to the barometer. The marine barometer[2] is quite special, not at all like the circular aneroid barometers seen on land. Instead it is a glass column filled with mercury. The scale on the side facilitates the reading of the top surface of the mercury. Atmospheric pressure controls the height of mercury in the tube. So a low pressure has a lower level of mercury and high pressure has a higher level.
The instrument is gimballed so the barometer stays relatively vertical during the motion of the ship.
[3]This is not the place for a technical discussion on weather systems. The navigators prime interested is how locally forecast weather will affect the ship in terms of wind, wave height and their direction. The changes in the barometer reading indicate to him the general status of local weather.
Then he focuses on 2 prime features of the weather, the type of cloud and their height and the wind direction and its current tendency. With that information, he can make decisions to reduce bad weather affecting the ship.
This is very important when a winter storm or hurricane is
near.
[4]The water surface by day also provides numerous navigational types of information. The swell and local waves help the navigator assess any danger to the ship's motion. Excessive rolling or pitching that can be a safety issue.
Changes in wind direction and strength help the navigator decide the most likely course to take.
By night
[5]The nighttime sky is a wonderful source of navigation items, the stars and the planets. They can be used to fix the ships position and give him also a relative course to steer by. First, he must identify these celestial bodies. The planets Saturn and Mars are easily identified in the northern hemisphere. Then there is the moon. The first star he searches for in the northern hemisphere is probably the Pole star.
Not very bright, but on a clear night observable. Its importance is that its altitude is also the ships latitude. A navigator can identify a range of stars useful for celestial navigation.
The sea surface
[6]The presence of ships or land and navigational symbols are constantly monitored by the navigator. The horizon is a special case. It is where he first sees the approach of other vessels and land. At night, the loom
of the lighthouse often appears long before the light itself. Constantly sweeping horizon is a fundamental requirement of the watchkeeper.
Convention on the International Regulation for Prevention of Collisions at
Sea (1972)
In addition to interpreting the natural marine environment, the navigator must be able to identify and interpret the actions of other users of the Maritime Highway.
The rules for this are embedded in the regulation for the
prevention of collision at sea, colloquially called the “COLREGS”[7]
He is trained to know each of the forty-one international navigational rules
for conduct of vessels at sea. In addition, he must be able to identify each
vessel on the sea and determine its actions. Is it a fishing boat, a ship not
moving, is it anchored?
Vessels display symbols by day and lights at night to indicate their status. For example, the ship at anchor displays a black ball in the bow by day and a single white light in the same position by night.
The common set of light for all vessels are their steaming
lights. They are white masthead lights, red port and green starboard lights and
a white stern light. In addition there can be other lights and symbols denoting
their current status.
Sound at sea
The navigator has a further sense he can use to effectively
navigate. His hearing. A deck officer must have good hearing. Discerning sounds
internally to the ship and externally and interpreting them is an essential
safety element in navigation.
Externally, it can be one of many sound signals used to
inform on the COLREGS. From changing direction, to abandoning ship or to
announce your presence in reduced visibility, the ships whistle, or horn is an
essential navigational tool. For example, three short blasts on the ships horn
indicates the ships is running its engines astern.
Other ships announce their presence or their intentions with
their horns or whistles. Light houses and buoys signify their presence in
reduced visibility conditions with foghorns or bells.
All this helps the navigator fixes the ships position.
Internally the watchkeeper must be able to respond
immediately to a range of sound alarms whether it be an equipment failure,
presence of fire or flooding etc.
There is another sense important to the navigator and that
is his sense of balance. A change in the motion the ship is instantly felt. Was
it an intended action or is this something the navigator needs to address? It
could be a change of course, the shifting wind or wave direction that is felt.
Sometimes it is a combination of all these senses that alert the navigator to
the changed status of the ship It could be changes in engine noise or vibration or alteration of
course that alerts the navigator to a change in the ships status.
The navigator must be constantly alert using all his senses.
References
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