# Calculating Longitude if I have D'Long and Departure or Arrival Longitude

Hi,
I don’t know where to put this question in forum, so I am writing it down here.
I would like to know if I have a d’long and a departure longitude, how can I find arrival longitude.
Also I would like to know how to do naming of the D’long and Arrival longitude.
Thanks
Ocean Learner

• The Question I am trying to do is: - Find the initial and final courses and the total distance on the composite GC track, limited to a maxmimum latitude of 55 Degree 00 Min. South , from 49 Degree 07 Min. South , 075 Degree 50 Min. West to 45 Degree 54 Min South, 170 Degree 46 Min. East.

http://www.csgnetwork.com/marinegrcircalc.html
Hopefully that helps.

Ocean,
First try looking in Bowditch Vol ll p. 575-613. If you don’t have a hard copy, do a google search and it should pop up. There will be several examples of “the sailings” in those pages. If you are familiar with trigonomtry: the Great Circle Sailing formulae for DISTANCE: Cos -1D=SinL1SinL2+CosL1CosL2cosDlo ////// for Initial Course: TanC=sinDlo / (CosL1TanL2 - SinL1*CosDlo)

The Sailings consist of the following:

1. MERCATOR / to find course and distance and to find lat and long of arrival
2. MID LATITUDE / to find course and distance, find course and distance when departure and arrival lat and long are known, to find lat and long of arrival
3. PARALLEL SAILING / to find distance, to find longitude of arrival
4. GREAT CIRCLE SAILING / to find distance, and to find initial course

I am a little unclear on the exact coordinates you posted. Maybe you can repost them for us. Sounds like a cool problem to be aware of.

[QUOTE=oceanlearner;66847]Hi,
I don’t know where to put this question in forum, so I am writing it down here.
I would like to know if I have a d’long and a departure longitude, how can I find arrival longitude.
Also I would like to know how to do naming of the D’long and Arrival longitude.
Thanks
Ocean Learner

• The Question I am trying to do is: - Find the initial and final courses and the total distance on the composite GC track, limited to a maxmimum latitude of 55 Degree 00 Min. South , from 49 Degree 07 Min. South , 075 Degree 50 Min. West to 45 Degree 54 Min South, 170 Degree 46 Min. East.[/QUOTE]

This problem is a “composite sailing” problem. You probably will first have to learn to solve great circle problems. I leaned “The Sailings” fromBowditch Chapter 24

K.C.

## Hi, Thanks all for your help, I will try to grab to grab a copy of Bow ditch from library, although I was able to do the question in later part of the day. I am posting the Co-ordinates again, for anyone who would like to give it a try.

The Question I am trying to do is: - Find the initial and final courses and the total distance on the composite GC track, limited to (maximum latitude of 55 Deg 00’ S) , from 49 Deg 07’ S , 075 Deg 50’ W to 45 Deg 54’ S, 170 Deg 46’ E.

You should be able to find it as a PDF download. If not shoot me a PM w/ email addy and I’ll send it along - big files but so worth having!

[QUOTE=mtskier;66889]You should be able to find it as a PDF download. If not shoot me a PM w/ email addy and I’ll send it along - big files but so worth having![/QUOTE]