Welcome to the NavList Message Boards.

NavList:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Position-Finding

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
    Re: Longitude sight, South Pacific, 1864
    From: Ed Popko
    Date: 2018 May 9, 04:39 -0700

    A very nice example. I have never disassembled one of these, Frank has already done it.  I have tried to annotate the lines I think I understand  marking those I don't or can't read with a question marks.

    Below the listing are my speculations as to what this ship might have been doing there.

    Bowditch 19th Century Logarithm Method

    General

    1              Dec of Sun    S 16º44’32” might be Nautical Almanac hourly value

    2              ?First corr                 6’        seems too much for 17 minute increment past the hour

    3              ?Exxx xxx          16º 50’32”  sum lines 1 and 2

    4              ? Corr xxx                   4’ 

    5              Second corr    16º 54’32”  sum lines 3 and 4

    6              Radian 90º

    7              Polar Distance 73º 05’28” = 90º - 16º 54’32”

    8              ? Sun’s altitude rounded  16º 34’  Lower limb

    9              ? altitude correction, possibly dip combined with lower limb  10’

    10           Altitude with corrections applied  16º 44’

    11           Latitude rounded 24º 03  (from DR or LAN)

    12           Polar Distance rounded down 73º 05’

    13           Sum of Altitude, latitude and polar distance   113º 52’ = 16º 44’ + 24º 03’ + 73º 05’

                    (Sum of lines 10, 11 and 12)

    14           Half Sum of  line 13       56º 56’ = 113º 52’ / 2

    15           Altitude from line 10     16º 44’

    16           Remainder = Half Sum – Altitude       40º 12’ = 56º 56’ – 16º 44’

     

    Local Apparent Time to Local Mean Time

    17           Local Apparent Time  05:15:18  =  78.8250º =  2 * 39.4125º   line 25

    18           Equation of Time         00:16:04  (fast)

    19           Local Mean Time         04:59:14  =  05:15:18 – 00:16:04

     

    20           Logsec(lat)     line 11             03944 = logsec(24º 03’)

    21           Logcsc(pDist) line 12             01921 = logcsc(73º 05’)

    22           Log Half Sum line 14          9,73689

    23           Log Remainder  line 16     9,80987

    24           Log total 9,80270  =  logsec(lat) + logcsc(pDist) + logcos(Half Sum) + logsin(Remainder)

                    (lines 20 21, 22 23)

    25           Logsin(LHA/2)   line 24      9,80270   LHA/2 =   39.4125º

     

    Time corrections and conversion to longitude

    26           Chronometer time Nautical Day                      01:01:00

    27           Chronometer rate compensation                    00:16:24 slow

    28           Chronometer corrected time (lines 26 + 27)  01:17:24

    29           Correction of 12hr for Civil Day                      +12:00:00 hrs

    30           Chronometer time Civil Day GMT                    13:17:24

    31           Local Mean Time  line 19                                   04:59:14

    32           Meridian Angle, ‘t’ or longitude as time  08:18:10  = GMT  (line30) – LMT (line 19 or 31) 

    33           Conversion 8 hrs to angle        120º = 08hr * 15

    34           Conversion 18 min to angle     04’30” = 18min/60*15

    35           Conversion 10 seconds time to angle  02’30”

    36           Longitude      124º 32’30” = 120º00’00”  +  0º04’30” + 0º02’30”    sum of lines 33 to 35

    Guano Expedition

    This ship is located just south of the Tropic of Capricorn. Perhaps they were going to or returning from Ducie Island, part of the Pitcairn Islands. A U.S. government expeditionary ship? Commercial guano miners? In 1867, Ducie Island it was claimed by the United States under the Guano Islands Act. Although Captain Edward Edwards discovered the atoll in 1791, Ducie was not considered a British possession.[Wikipedia] In 1867 Ducie was claimed by the United States under the Guano Islands Act, which established that an uninhabited territory with guano deposits could be claimed as a US possession, so long as it was unclaimed by any other country.

     

    Whaling

    Possible this ship was hunting whales though it’s on the southern most boarder of the “Offshore Grounds”. Below is Matthew Fontaine Maury’s famous 1851 Whale Chart (Source: Washington, D.C., Naval Observatory, 1851. Color lithograph. Geography and Map Division). 

    Ed Popko

    File:


    File:


    File:


    File:


    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
    Email:

    Email Settings

    Posting Code:

    Custom Index

    Subject:
    Author:
    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site