# NavList:

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

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Re: Relative bearings
From: Henry Halboth
Date: 2015 Apr 18, 14:41 -0400
Greg,

Your reference to the "Radian Rule" bings to mind the Special Bearing Cases in which we were drillrd in the days when the mate on watch was expected not to leave the bridge, especially at night, to consult the chart or any form of publication. See attached summary of cases.

Henry

On Tue, Apr 14, 2015 at 6:46 PM, Greg Rudzinski wrote:

Bill,

When working with true and magnetic bearings to be plotted on a chart you will be using the pelorus 0° clockwise to 360°.  If doubling the angle on the bow or using Bowditch table 7 (1981)/table 18 (2002) then work port and statboard off the bow or stern. There is also the radian rule which is worked port and starboard off the bow. see link:

https://www.youtube.com/watch?v=Q8sJcePmziM

Greg Rudzinski

From: Bill B
Date: 2015 Apr 14, 14:34 -0700

Recently viewed a page at the URL below and it struck me as vague and misleading regarding "relative bearing" and pelorus use:

http://www.gosailing.info/Navigation%20-%20Relative%20Bearings.htm

I've always regarded relative bearing (RB) as a 0-360d measurement with the bow-end of the lubber line being O. The above article seems to suggest it is always measured 0-180 CW on the starboard side and 0-180 CCW on the starboard side. Also that a pelorus card is always set to 0.

I consider RB starboard and RB port to be a subset of RB. Borrowing from submariner terminology it makes communications/notations easier for me to use "Angle of the bow" or "AOB" noting port or starboard when necessary.

My calculations use the following (True bearing = TB, compass = C)

AOB or RB starboard = RB

AOB or RB port = 360 - RB

RB = TB + C

TB = RB-C

C = RB - TB

Add or subtract 360 if less than 0 or greater than 360 respectively.

Any opinions on standard usage of RB and AOB?

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