NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Longitude by Time Sight...good enough at sea?
From: Doug MacPherson
Date: 2012 Dec 19, 20:06 -0800
From: Doug MacPherson
Date: 2012 Dec 19, 20:06 -0800
All:
I appear to have narrowed down my navigation "solution" for the parameters I have set for myself:
--
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:
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
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
On Mon, Dec 17, 2012 at 10:41 PM, Hewitt <hhew36@gmail.com> wrote:
Greg-
Tonite with specs and 20" I came up with an LHA of 69* 49'. Hmm . . . Time to get the lead out? ;-) Or maybe I better deep six the specs.
Hewitt
Sent from my iPad
> Attached File: http://fer3.com/arc/img/121462.img_1736.jpgOn Dec 17, 2012, at 7:38 PM, "Greg Rudzinski" <gregrudzinski@yahoo.com> wrote:
> Hewitt,
>
> Not to worry. I have a hand lead at the ready ;-)
>
> The attached shows an afternoon time sight reduction using trig and trig log tables from Bowditch.
> 10 table entries and 4 sums were required. The slide rule solution is so much easier by comparison.
>
> Greg Rudzinski
>
>
>
> [NavList] Re: Longitude by Time Sight...good enough at sea?
> From: Hewitt Schlereth
> Date: 17 Dec 2012 15:56
> Greg, this time I got a LHA of 62* 12' which gives a Lon of 119* 11' W. So
> look over the side to be sure you're not aground.
>
> My only excuse is this time I worked without my 4-power specs. :-)
>
> Hewitt
>
> ----------------------------------------------------------------
> NavList message boards and member settings: www.fer3.com/NavList
> Members may optionally receive posts by email.
> To cancel email delivery, send a message to NoMail[at]fer3.com
> ----------------------------------------------------------------
>
>
>
>
>
> : http://fer3.com/arc/m2.aspx?i=121462
>
>
--
Confidentiality Notice: This electronic transmission, including attachment(s), is covered by the Electronic Communications Privacy Act § 18 U.S.C. 2510-2521, and is for the sole use of the intended recipient(s). Unauthorized review, dissemination, disclosure, or reliance on the content(s) of this transmission is prohibited.
