A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Mark Coady
Date: 2017 Jun 20, 03:58 -0700
Sadly I am typing on my phone. I can't send a sketch at the moment.
There are a couple of good points here.
One big one is how much weight you put on a DR position and when do you toss it in favor of a multipoint celestial fix.
If I dropped the perpendiculars to the lops from the DR in your example, depending on error circles i would land pretty close to the right side of that ellipse, near the center of the large circle. That would put me neatly between the DR and the crossing of the LOP.
If I have one lop, and a DR, dogma dictates I drop the DR to the line and call it an EP. What if I have two lop's? Do I toss the DR, or wait till I have 3. In inshore work we cling to the DR and EP concept, until we have a multipoint fix we truly believe in. Our Dr's are based on experience and often really good.
In an open sea situation, after a four day sloppy gale, your conidence in your DR might be only that its not very good, and two sights are far better.
Raises issues in judgement. Which is certainly in the news this week. To add to the Navy incident, we had a nice schooner (Alabama) with a school field trip ground on wrong side of mark in Mystic Harbor entrance Sunday.