NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Mike Freeman
Date: 2019 Dec 20, 09:27 -0800
Thanks for replies.
Evident that not everyone is happy with Mary Blewitts method.
From what I have understood this method makes a plotting sheet specifically for the Latitude represented by the line drawn at an angle. If your LOP's come very close to the Latitude in question there will be little error but if the LOP's are say half a degree away from the designed Latitude then we have some error.
I found an online calculator - length of 1 degree of longitude for a given latitude.
I also realised also that the triangles created by the Mary Blewitt method could be solved mathematically. Found an online right triangle calculator.
I then multiplied the factor for latitude by the miles of longitude. Of course every answer should be 60M.
Results........
Lat Long (M) LAT Long Lat in nautical miles
45 42.57 1.41 1 60.02
45.25 42.39 1.42 1 60.19
45.5 42.2 1.43 1 60.34
45.75 42.01 1.43 1 60.07
46 41.83 1.44 1 60.23
46.25 41.64 1.45 1 60.38
46.5 41.45 1.45 1 60.1
46.75 41.26 1.46 1 60.23
47 41.07 1.47 1 60.37
The lat/long converter provided answers to many decimal places and to 2 decimal places. I just worked to 2 as you can see. The triangle calculator only works to 2 decimal places.
I was hoping to determine how much error would be present on the plotting sheet if the LOP was say half a degree different.
Mike
