NavList:

Doug,

If I were to go the full minimalist non-electronic route without losing sleep then sight reduction can be done with just a trig slide rule, 2 almanac pages of pub 249 table 4, formulae, and pencil. The slide rule ex-meridian is good to a few minutes of arc and the time sight by slide rule is good to about 10 minutes of longitude. At sailboat speed this means arrival will only be off by plus or minus a couple of hours from the last time sight. Daily runs can be done by slide rule mid latitude sailing. This is good enough without being classified as emergency navigation.

Greg Rudzinski

[NavList] Re: Longitude by Time Sight...good enough at sea?
From: Doug MacPherson
Date: 19 Dec 2012 20:06
All:

I appear to have narrowed down my navigation "solution" for the parameters I have set for myself:

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.

Thanks for all the great advice over the last few weeks.
For me, my preference at this point would be Norie's, with a copy of Hansen's Ex-Meridian tables. Primarily would use for latitude: polaris, ex-meridians and noon. For Longitude: time sights. This will be when far from land.
Near landfall, traditional LOP's for a fix.

Considerations:

I have both of these (Norie's and Hansen's) and am familiar with how to use them.
Norie's has 5 place natural/log haversine and log cosine function tables that are more accurate than Pub 229 and 249 satisfying item 5 in my list above.
Norie's has the ABC tables for azimuth, this enabling a quick LOP to be calculated if needed from an ex-meridian or time sight.
As needed the spherical triangle and azimuth can be determined with the cosine-haversine and ABC tables in Norie's.
The use of a slide rule seems intriguing and I think I will get one just to try it out, but don't believe it would have the accuracy of Norie's...item 5.
Similiarly, Weems LOP + Hanno Azimuth seem very good, but not as accurate as Nories....also, I need to get a copy of them.
If I could get a copy of Martelli's tables for time-sight that would make it a quicker look-up than Norie's, ( with similiar accuracy) I would consider that.

Clearly, preference 5, accuracy, weighs heavily in favor of Norie's. Without 5, many other (simpler) solutions would be very satisfactory.

Thanks again for all the great posts.

Doug

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