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Undergraduate Deck officer discover the secrets to chartwork, the result might surprise you

Just as the need for knowledge, wisdom and communication grow, the need for knowing the position and location of people, object or phenomenon where needed which brought about the discovery of maps; they describe an area, venues or zone. Its first development was with a sketch before the 1st century when an African known as Ra Edugo was telling his younger brother where they leave. So that in case he gets missing he could find his way home. The head villager appointed him to draw the route of every land they encounter. It's from this sketches that the first sea map separating two continents was drawn. Also know as continental map.

This later on brought explorers like Christopher Columbus to evolve it to chart work and use it in the discovery of the world.


In our era, we have grown so advance that we have additional navigational aids like; Radar, GPS, Sextant just to name a few.


CASE STUDY

NB: For most chart this days;Yellow stands for land, Blue stands for shallow waters and rivers, White stands for the sea.

  1. Fixing position of latitude and longitude.

Here we seek the position of the object, area or zone give by the latitude & longitude. Latitude is measure vertically while longitude is horizontal. Since the most chart are large extract, you don't need to worry about the measuring the lat & long again. Also modern chart this day use AI which pretty well provide the result in fractions of a second. But till you have to study to be eligible to use those machines.


Specific Item: a Ruler or two


  1. Fixing positions with bearing and distances from lighthouse, buoys....


Have you ever hear the saying ,”No matter how fast you run time always catches up to you”. It's the same here. To begin with;

  • Plot the position of X ( little piggy )

  • From this initial position plot the vessel's course. At the end of the run when it equals the vessel's speed and time interval. Apply the current direction

  • Along the current mark the drift over the whole time period ( drift = rate x time interval for the vessel to move from A - B )

  • Join the end of the drift to the vessel's initial position.

  • The end result is a triangle, not a perfect triangle for it's not a most for it to be. From it you can get the vessel's; Course made good with two arrows, Speed made good and Estimated position which is slightly a more accurate estimate of the vessel's position than Deck reckoned position (DR). By taking into account the vessel's movement and the effects of leeway ( is the difference in angle between the course steering with one arrow and vessel's track; ignore speed of wind ) and SET.

    NB : You might need to learn a couple of symbols that refer to features on the map you are working on.

  • The best way to obtain course made good is to put your “parallel rule” on the side with two arrows, transfer it to the compass rose ( center point ) and read the angular figure.

  • The best way to obtain speed made good will be to use your “divider” to measure the distance along the course made good line and divide it by the time interval.

  • The best way to obtain the estimated position {EP} after W hours will be to read the lat & long on the appropriate scale and record it.


Specific Items; Parallel rule, divider

 


  1. Fixing positions by cross bearings.




Steps in solving Running Fix with only Current
1. Plot the first bearing of the Lighthouse.
2. Plot the second bearing of the same Lighthouse.
3. Choose any point on the first bearing.( Choose your own point. Not what someone has chosen)
4. Plot the ship's course through this chosen point.
5. Using the given ship's speed and time interval calculate the distance covered(Run) along the ship's course.
6. Apply the current at the end of the run.
7. Join the initial chosen point to the end of the current. This becomes the EP.
8. Transfer the first bearing through the EP, where it cuts the 2nd bearing becomes your NOON POSITION.
10. Transfer the Course made good line through the Noon Position, where it cuts the first bearing is your position at 9am or 10am whichever is applicable.

  1. Plotting courses on the chart.


Steps in solving Horizontal Sextant Angles.

1. You will be given 2 to 3 or even more fixed positions on the chart to take references from with their respective angles from your ship or a ship.

2. Fixed positions on the chart can be represented by many things ( buoy, lighthouse, post, another vessel). 

3. With the use of a 180° protractor, a 15 cm ruler, a metal compass, a 9 cm pencil, a pencil sharpener, an eraser and a 10mm stencil; all equipment found a modern math set.

4. Draw a straight line with a sharp pencil linking all fix positions. (Most of the time you might have an imaginary triangle depending on how far the fixed point are from each other)

5. Use the protractor to find the corresponding angles of the fixed positions with respect to the ship's position.

6. From where the same corresponding angle meets between two lighthouses (fix position). Draw a circle with a metal compass from that position passing via both lighthouses.

7. Repeat "step 6" if you have 3 or more lighthouses.

8. Now, where the two circle intersect each other represents your ships position.

NB: The depth of the sea from the ship can be read from the chart if you are asked for it.

With that said, the is also a third was to confirm your ship's position but, I will leave it to you. Hint (use the third bearing of the lighthouse which is usually the sum of the first to second and second to third bearing. You will also have to draw a straight line joining both (1st and 3rd). Repeat step 1 to 6 and you are done).

NB: For deck officers under training in the tech age, Ship simulation are provide in most marine academies to  help the new newbies have a taste of the field.













Location:Ghana Accra, Ghana

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