NavList:

Gary,

I am with you on what is possibly being labelled as emergency navigation only. Compact/Ultra Compact doesn't automatically classify a method as being practical only in an emergency. There is perhaps a grey area where a method isn't quite good enough for everyday use on a ship but good enough for small craft. For me the line is drawn at 2' of precision for everyday use on a small craft and 1' of precision for everyday use on a ship.  Emergency precision should be no worse than 10' which is about the width of a pencil line on a pilot chart and about the distance to the horizon from the bridge of most ships. 

Ship/ Small Craft  Primary CN SR Methods:

1. Calculator, 229  (0.1')

2. 208, 211, 229 Schlereth, Weems, Hav Doniol, Original Bygrave, 249 (1.0')

Small Craft Primary CN SR Method:

1. Flat Bygrave (2')

Emergency CN SR Methods

1. Brown Nasau, 10" slide rule Bygrave, 8" circular slide rule Classic Trig (5') 

2. 10" slide rule Classic Trig  (10')

To me it looks as if all the methods can be classified as compact except for 229 and 249.

A third class of Ultra Compact would include the following as practical for everyday primary use on a ship:

1. Pocket Trig Calculator, Otis King w/ natural trig table, Original Bygrave, Hav Doniol. 

Greg Rudzinski

From: Gary LaPook
Date: 2015 Jul 14, 00:22 -0700

BTW, I don't like calling these "emergency navigation" systems. That implies using a less accurate system for celestial navigation in emergencies whose only advantage is that they are compact so as to fit in a ditch bag. This seems to say that you use the most accurate standard system everyday, carrying the entire set of HO 229 in your small boat, and will  use the bastardized system only in an emergency. What we are actually talking about are different methods of clestial navigation, that just happen to be compact, but that should be used every day for normal celestial navigation, leaving the entire set of HO 229 at the dock. Most navigators have apparently shifted to using HO 249 to save the considerable space (and weight) of the ultimate set of tables, HO 229, and find the level of accuracy in HO 249 accptable for practical navigation and the Bygrave and Hav-Doniol (and others) provide the same level of accuracy in very compact forms.