A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2021 Mar 9, 08:54 -0800
Tony Please see below:
Dear David, I'm asking not only about being late to the DR point because of the extra time spent to fly longer track while determining the wind vector.
I think you mean turning point or objective. You can't be late for a Ded Reconning point, because it's where you deduce you actually are. That said, they do say some people would be late for their own funeral, but I don't think Chichester fell into that category.
I suppose he might have needed to worry about keeping reasonably on time, because he'd worked out a final Sun position and the track for his final approach to Norfolk Is before take-off. If he was very late, he'd be working with some quite large 'motion of the body' corrections, because the Sun races west at 15' longitude per minute. It's azimuth would be reducing also.
Should we also account for being leeways after the wind vector determination? That is my question.
The whole point of the air plot method is that you only apply wind (leeway) to your air position (the place you would be if the wind was zero) when you want to find your DR position. Chichester has cheated a bit by using the same plotting lines to find both the W/V and his DR position. By rights, to get his DR position, he should have moved his air position back along course by the distance he lost doing the 30° dog-leg and applied the wind he'd just found to the revised air position to obtain a better DR poition. E.g. flying at 60kts for a 2 minute leg 30 degree dogleg, his DR position would be 4x(1-cos30) = 0.54 nm back towards NZ, barely the thickness of a pencil line on the size of chart he was probably using. DaveP