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Re: Video of Davis MK 3 Practice at Sea
From: Brad Morris
Date: 2019 Oct 6, 17:28 -0400

Hi Greg

I did not know you were a fan of Delos!

I watched the video until they discovered how far off they were. I have some small issue with recovering time from a GPS unit, but that is just a quibble.

I understood how they achieved a small latitude error. It is a LAN observation. That should be relatively close. They get a 3nm error

What is completely unclear, from the video, is how they determined longitude. They just announce what they get and compare it to the GPS. I suspect they found the apex of the sun altitude curve, estimated the UTC of the apex, and did the time delta to longitude conversion.

Brad

On Sun, Oct 6, 2019, 4:34 PM Greg Rudzinski <NoReply_Rudzinski@fer3.com> wrote:

It is a little difficult to find course, speed, assumed position, and then make sense of working notes which may be for a different day. What I am getting is an assumed position of 22° 6.2' N 76° 11.9' W at UT 17:30:00 off the GPS. The example observation made by the crew member (perhaps his first ever) has Hs 84° 10' lower limb Sun marked at UT 16:45:20. Course is 239° true? speed 6kts. The date is in question but seems to be 7/13/2019. LOP plots ok. Well done crew member! An index error of 5' on the arc was used on the working notes but not labelled. Semi diameter,refraction, and dip aren't labelled either. I am also wondering how he was able to keep from burning his eye some when bringing down the Sun since the mark 3 doesn't have horizon mirror shades :0
Greg Rudzinski

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