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Re: Longitude by Time Sight...good enough at sea?
From: Doug MacPherson
Date: 2012 Dec 13, 20:16 -0800

Wow, Great discussion. Really appreciate Frank's insight on the Sumner Line and the time sight, also the other great stuff sent my way.

For me, the choice of the time sight and ex-meridian etc. comes down to my parameters for what I want from my navigation "solution".

There are many solutions out there. From the gyro/satellite (electronic) solution I was using as a bridge officer in the USN in the 80's, to the Polynesians navigation system (relying on the sun and stars, winds and clouds, seas and swells, and birds and fish) and everything in between. Choose your parameters and then the solution will follow, i.e. electronic/non electronic, tables/non tables etc.

My current parameters include:

1. Non electronic and based on accurate sextant measurements and an accurate chronometer.

2. As little plotting as possible.

3. As little tedious mathematics (prone to mistakes) as possible.

4. As few books as possible: Norie, Bowditch, Hansen are OK. One book vs. volumes.

5. The best accuracy possible given 1 through 4.

Given all your helpful feedback, my solution would appear to include: Latitude by Polaris, Latitude by Ex-Meridian, Latitude at noon and Longitude by time sight. Books to include, a up to date nautical almanac, Norie's (or Bowditch), Hansen's, and some tables for time sight (Martelli?), (although I am happy with Norie's and the haversine formula's for the time sight). These would appear to be enough.

Certainly, if safety required, the LOP would be utilized (modern methods) .....as well as the handheld GPS :)

Thoughts?

Thanks,

Doug

On Thu, Dec 13, 2012 at 3:23 PM, Greg Rudzinski <gregrudzinski@yahoo.com> wrote:

Hewitt,
I have not seen the Weem's secant table for time sights. I have seen the Rust diagram for azimuth which is not as good as Hanno Ix's azimuth diagram. The Weem's 9 page secant table for time sights sounds very interesting and could be combined with the Ix diagram to create an ultra compact sight reduction method.

Greg Rudzinski
[NavList] Re: Longitude by Time Sight...good enough at sea?
From: Hewitt Schlereth
Date: 13 Dec 2012 14:05
Frank and Greg -
Have you seen Weems' The Secant Time Sight. Nine-page table and Rust for azimuth gives you an LOP. I used to have it in my sextant box for 'when else failz' backup. :-)

Hewitt
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