NavList:

Hewitt,

Attached is a K&E 10" time sight reduction for this morning that is within 2' of longitude of a calculator reduction.

Your 20" should be able to improve on this a little.

Greg Rudzinski

[NavList] Re: Longitude by Time Sight...good enough at sea?
From: Hewitt Schlereth
Date: 16 Dec 2012 21:39
Greg, I did unpack my 20" K&E 4081-5. The slide was a little sticky - been sitting in its mailing tube for a year. Anyway, using your time sight data and a pair of 4X drugstore reading glasses I got an LHA of 61* 12' for a longitude of 119* 12'. Not a significant improvement from your results with a standard size rule.

Hewitt

Sent from my iPad

On Dec 13, 2012, at 8:45 AM, "Greg Rudzinski" <gregrudzinski---com> wrote:

Doug,

I just did a time sight of the morning Sun (my first ever time sight) using my exact latitude and then a latitude that was off by 6'. The 6' change in latitude shifted the longitude by about 6'. This puts it in the realm of good enough even when away from the prime vertical.

The Formula:

LHA(t) = ArcCos [ (SinHo ~ SinDec * SinLat) / (CosDec * CosLat)]

Ho= 8* 21'
Dec= 23* 12' S
Lat= 34* 10.4' N

UT = 15:46:22 12/13/2012
GHA = 58* 00.0'
GHA + (t) = 119* 11'
GPS Lon. 119* 13.8' W

If this example is correct then the calculations are not too involved as you previously stated.

Greg Rudzinski

[NavList] Re: Longitude by Time Sight...good enough at sea?
From: Greg Rudzinski
Date: 11 Dec 2012 15:50
Doug,

What a great find ! With spectacular historical provenience no less. A sure keeper for the chart table library. Be sure to keep it in a zip lock to protect from splash or photo copy the needed pages for on the water use.

For your expanding list of traditional observations I would add longitude by equal altitudes (if latitude sailing) and daytime ex-meridian of the Moon when present. It may also be necessary to use bodies other than the Sun to obtain a time sight since the Sun isn't crossing the prime vertical year round.

Keep in mind that the ex-meridian isn't perfect. The further the body is from MP the less reliable the latitude. A good DR position is required.

Greg Rudzinski

[NavList] Re: Longitude by Time Sight...good enough at sea?
From: Doug MacPherson
Date: 11 Dec 2012 15:17
Hello Greg:

I just got a copy of Hansen's from 1915. The inside is signed by HA Jeams of the SS Sonoma...November 20, 1918. Googled the Sonoma, great history to an ocean going tug that served in WW1 and WWII, eventually being destroyed by a Japanese bomber that crashed into it in the South Pacific.

What a handy book and set of tables!

So as I continue to find the daily navigation routine to be used at sea, far from a landfall, that:

1. uses no electronics.
2. Has a minimum of plotting
3. And a minimum of calculations

Here is what I am now thinking.

1. Pre-Dawn Latitude by Polaris or Ex Meridian Latitude using Hansen's (for moon, planets or stars close to meridian)
2. Early morning Time Sight for Longitude.
3. Late morning Lat using Sun and Hansen's Ex Meridian.
4. Latitude by Noon Sight.
5. Early afternoon Latitude using Sun and Hansen's. Ex Meridian.
6. Late Afternoon Time Sight for Longitude.
7. Post-Sunset Latitude by Polaris or Ex Meridian Latitude using Hansen's (for moon, planets or stars close to meridian)

Your thoughts?

Cheers,

Doug

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