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Ship’s position by Long by Chron and Merpass: Here is how to get it

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sun-sight-sextant The World has evolved enormously and so has the technology. Google has mapped the world so extensively that you can literally put the house number of a friend and google map will take you to entrance door of his house. When the world has become so advanced it looks so outdated to talk about things like sextant. But anything that works independant of any external resource will be valued for ages to come. Sextant is one such equipment on board the ships. And because it is independant of any external resource, you still have it on board. And because it is going to be there for long time, it is time that we know it better. I have written a couple of articles on sextant and how it helps to get the ship's position. Article such as How do we get ship’s position by star sight ? How a Marine Sextant Helps in Getting Ship Position ? In this post, I will discuss about getting ship's position by Sun sight. Let us begin. 1. Getting the DR position The first thing that we must know is our DR position. We cannot expect to suddenly land ourself in the middle of the sea. We must be aware of our whereabout. To know the DR position of the vessel, we just get the last known position of the ship and apply our course and speed to that position to get the present DR position. This is not so dif...

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Comments (20)

  • Ivan September 10, 2018
    Thank you very much sir for such a clear explanation. Waiting for more articles sir. Request: position by intercept sun and stars.
    2
    Rajeev Jassal October 14, 2018
    Thanks Ivan...
    Rajiv Kumar Singh January 25, 2020
    sir which method is most useful long by chron or intercept?
  • Kamil September 16, 2018
    Okay, how about plotting celestial LOP and poaition on ECDIS ?
    1
    Rajeev Jassal October 14, 2018
    We have to calculate the position from the sight calculation and plot this position on ECDIS. No need of all those lines to be plotted on ECDIS.
  • Vimal Kumar November 9, 2018
    Sir, Could you give me your mail Id or something as I have a personal doubt regarding my career and wanted to ask you a query regarding it.
    0
  • Ajay Achuthan November 10, 2018
    Goid explanation Just a few corrections. Please contact me on email
    0
  • Capt. Ahsan Bin Aslam November 11, 2018
    A brilliant walk down the memory lane, the days of real navigation. Capt. Rajeev, keep up the good work.
    0
  • Panagiotis Tasios November 15, 2018
    Good Day Captain. I much appreciate your efforts to share in public such useful information. Thank you.
    0
  • Prem Choudhary December 14, 2018
    Why do use Long by chron in morning and Intercept in evening for sight calculation?
    0
  • Alok Singh January 29, 2019
    How I wish that books were written in such a comprehensive yet simple manner.Thanx a ton for all the blogs here sir.
    0
  • Halifa February 20, 2019
    I wonder if can we get positon without sun merd passage time ? Let say we get first line at morning sight 0833 then after 2 hours will get again a morning sight. Is it possible sir ?
    1
    Mohammed Ansari January 3, 2020
    What u ll do with two observed longitudes
  • Mayank June 4, 2019
    Sir, what if we take sights of 3 stars in the morning/evening and solve it by long by chron by applying for time difference. Will we get a fix by that ? How will that fix be different than Intercept method ? Thank You
    0
  • Rishab July 3, 2020
    Wow, just the way you explained each step is mind-blowing. Very detailed, yet interesting. Extremely well written and presented. Very impressive.
    0
  • Robin September 2, 2020
    It's really helpful sir.. thank you
    0
  • Anupam Kumar Tiwari December 12, 2021
    First calculation is i.e Long by crone is done on 1st May 2018 @ 0033 UTC ,so why the Merpas calculation is done on basis of date 2nd May 2018. Both the sight is happening on same day .
    0
  • Abrar May 12, 2022
    "Thanks for sharing such an amazing blog. I have learnt alot from it. For more information visit https://www.mvvsmaritime.com/"
    0
  • Abrar May 12, 2022
    "Thanks for sharing such an amazing blog. I have learnt alot from it. For more information visit https://www.mvvsmaritime.com/"
    0
  • Capt. Ali October 13, 2022
    Thanks dear Capt. Rajeev.Well done.Awiting for grate circle & coastal navigation lessons.
    0
Capt Rajeev Jassal

About Capt Rajeev Jassal

Capt. Rajeev Jassal has sailed for over 24 years mainly on crude oil, product and chemical tankers. He holds MBA in shipping & Logistics degree from London. He has done extensive research on quantitatively measuring Safety culture onboard and safety climate ashore which he believes is the most important element for safer shipping.

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