# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

**Re: Azimith forumula for Great Circle sailings- having problems**

**From:**Samuel L

**Date:**2014 Dec 24, 11:42 -0800

'Don't know what to say. You guys are discussing super-precise accuracy. I'm just trying to get an answer to the Azimith in great circle sailing problem.

Here's the information I've been relying upon.

Bowditch Chapter 24, The Sailings, page 347 shows the procedure to obtain distance and initial bearing between 2 locations using HO 229.

Bowditch Chapter 22, Calculations and Conversions, page 332 gives the distance and initial bearing formula.

The man at the link below mentions a formula for calculating distances and bearings between 2 places on earth.

http://www.madinstro.net/sundry/navcel.html

My question still remains unanswered- what formula should I use to solve the intial bearing? As to distance- I get the results that are correct enough for my use. Also, in posts back in 2005 there was much discussion on what formula to use.

The formula mentioned at the top of the post in the next below this line is the one I've been using as of recently.

http://fer3.com/arc/m2.aspx/Azimuth-Formula-Questions-Tschudin-oct-2005-w26096

Notice in the post below the man says you can use the formula for Great Circle sailing.

Here- http://fer3.com/arc/m2.aspx/Azimuth-Formula-Questions-Simmonds-oct-2005-w26098

**Re: Azimuth Formula Questions****From: **John Simmonds**Date: **2005 Oct 23, 23:58 +1000

**the same formula will work for great circle sailings**

**enter departure as assumed position .. destination as LHA & Dec**

On Sun, 23 Oct 2005 11:58:10 +0300, Marcel E. Tschudin wrote:

>�George, you suggested this formula to calculate the azimuth

>

>>�az = arctan (sin (hour angle) / (cos (hour angle) sin lat - cos

>>�lat tan dec))

>>

>>

>�Do you know of a formula with the same advantages as the one you

>�mentioned here in order to calculate the azimuth for the direction

>�between two locations on the globe? The spherical triangle formula

>�which I am using at present needs a lot of if-statements for

>�selecting the right quadrant. May be there does also exist a more

>�advantegeous formula to calculate this azimuth.

>

>�Marcel