WHERE ARE WE?

Mayur Kande GP II – Roll No: 7453

29 Jun 2016


One of the most basic duties of an officer of the watch (O.O.W) is to obtain the position of his ship from time to time and mark thesame periodically on the navigation chart. In doing so he most dutifully answers the question frequently asked by the Master, “Where are we now?” It means where exactly on the navigation chart is the present position of the ship? The mariner must be ready with the answer in a jiffy. A navigator must ascertain that his ship is proceeding along the intended track without much deviation.
There are various methods of position fixing on the ship. Some are most rudimentary, whilst others are most advanced and sophisticated. It all depends upon the facilities available at the rolex gmt master ii replica disposal of the mariner within and beyond his ship. For position fixing the navigator utilizes visual land marks, radio aids or observation of celestial bodies. But when these facilities are not available due to restricted visibility or overcast sky or due to the unreliability of radar bearing and range, then the only method left to be used for position fixing would be Dead Reckoning (D.R.).
Dead Reckoning is the process of determining one’s present position by projecting course and speed from a known past position and further predicting a future position by projecting course and speed from known present position. Dead Reckoning position is only an approximate position because it does not allow for set and drift, wind and leeway, helmsman error or compass error.

Dead Reckoning (D.R.) helps in determining Sunrise and Sunset, in predicting landfall, Sighting lights and predicting arrival times and evaluating the accuracy of a ‘fix’ obtained by using electronic position lines. It
also helps in predicting the celestial bodies which will be available for future observations.
But most importantly it is used to project the position of the ship into the immediate future and avoiding hazards to navigation. A fix taken at each D.R. position will reveal the effect of current, wind, helmsman error and allow the navigator to stay on the track by allowing for all the above short falls.
In the latest type of Bridge Navigation, the ECDIS – Electronic Chart Display and Information System is put to use as a primary plotting method. But until the ECDIS is proven to provide highest standards of safety required in position fixing, the use of the traditional plot is a prudent back up especially in restricted waters. The following procedures apply to DR plotting on traditional paper charts.
Plotting the D.R. position should be done as follows: replica watches
1. At least every hour of navigation watch.
2. After every change of course or speed.
3. After every fix or running fix.
4. After plotting a single line of position.

For making a DR plot, a known start point should be plotted on the chart. Then, a straight line is drawn on the chart to represent the movement of the ship over earth’s surface – course. After allowing for the time interval for which such course is steered, we can easily know the new D.R. position of the ship. The D.R. position is marked by a circle over the water track Over and above though approximate, Dead Reckoning is the only available method of position fixing when the ship is on the ocean passage and when position lines are not easily available.


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