NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Dip from Shore
From: Gary LaPook
Date: 2016 Feb 10, 01:16 +0000
From: Jim Rives <NoReply_JimRives@fer3.com>
To: garylapook@pacbell.net
Sent: Tuesday, February 9, 2016 11:23 AM
Subject: [NavList] Re: Dip from Shore
From: Gary LaPook
Date: 2016 Feb 10, 01:16 +0000
Shoot latitude lines since they are inherently more accurate than longitude lines. It is hard to get the time more accurate than 1 second which makes a .25 NM error band. then the published GHA is rounded to 0.1' accuracy adding another 0.1' uncertainty. Then the "increments" table also has that same 0.1' round off. If you use the GPS position as your AP to just a 0.1' precision then you get another 0.1' uncertainty. If shooting a star then add an additional 0.1' for the SHA and if shooting a planet then you get a 0.1' uncertainty from the "v" correction (actually a bit larger since you do a multiplication step in determining the "v" correction.)
Much less uncertainty with latitude sights.
gl
From: Jim Rives <NoReply_JimRives@fer3.com>
To: garylapook@pacbell.net
Sent: Tuesday, February 9, 2016 11:23 AM
Subject: [NavList] Re: Dip from Shore
I hadn't even considered wave height. One of my future (ie, ain't gonna ever happen) projects would be to run multiple iterations of a sight reduction program, a round of say 4 or 5 well placed objects, and just increment the dip by 1 foot each round to see if the fix closes in on the real height of eye.
The odd thing I've noticed since recently trying to get back into taking sights is how similar snagging just the right time to "mark" is to deciding when to actually pull the trigger in shooting a target rifle. It seems to become less of a physical thing and more of a feeling. Probably becomes second nature.... I used to shoot probably a dozen shots a day while at sea and never gave it a thought.
Jim
