Welcome to the NavList Message Boards.

NavList:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
       
    Reply
    Re: Silicon Sea : Leg 69
    From: Dan Hogan
    Date: 2001 Apr 09, 23:01 EDT

    On 9 Apr 2001, at 11:43, Michael Wescott wrote:
    > I tried sending this once before but it seems to have gotten lost ...
    >
    > Well this one has me stumped. I'm either missing something, or I'm
    > so rusty that I'm a danger to myself and others should I get on my
    > boat anytime soon.
    >
    > >
    > > Dead-Reckoning problem     Leg 69  040401   Test your knowledge!
    > > ----------------------     ------  ------   --------------------
    > >
    > > The last DR position was(10d 27.9'N 52d 26.4'W) on 18/05/2000
    > > {at}XXX.XXX Dev
    > > 1.5dE. Current Set 285d Drift 0.5Kts.
    >
    > Figure roughly 10hrs {at}XXX.XXX Using traverse tables
    > for 289 d we get
    >
    > D.Lat =  34.8
    > Dep   = 101.2
    > D.Lo ~= 101.2 / cos 11 = 103.1
    >
    >         10  27.9N       52  26.4W
    >             34.8           103.1
    >         =========       =========
    >         11  02.7N       54  09.5W
    My computed answer DR--11d 01.7'N  54d 06.3'W
    You are OK a good answers when using Traverse Tables.
    >
    > Using A.P. of 11 00.0 N  and  54 00.0 W.
    >
    > > On that evening we take the following sights:
    > >
    > >         Body            UT                  Hs
    > >
    > >         Sirius          22:15:30            28d 16.3'
    > >         Spica           22:17:02            42d 20.6'
    > >         Avior           22:19:00            15d 55.3'
    > >         Bellatrix       22:19:45            13d 26.5
    > >         Dubhe           22:20:12            37d 56.1'
    >
    > > 1)  What is our FIX position?
    > > --  -------------------------
    >
    > Using AP 11N 54W:
    >
    >              Sirius       Spica     Avior     Bellatrix   Dubhe
    > UT          22:15:30    22:17:02   22:19:00    22:19:45  22:20:12
    >
    > Hs           28 16.3     42 20.6    15 55.3     13 26.5   37 56.1
    > IC              -2.5        -2.5       -2.5        -2.5      -2.5
    > Dip (9')        -2.9        -2.9       -2.9        -2.9      -2.9
    > ========    ========    ========   ========    ========  ========
    > Ha           28 10.9     42 15.2    15 49.9     13 21.1   37 50.7
    > R               -1.8        -1.1      -3.4         -4.0      -1.2
    > =======     ========    ========   ========    ========  ========
    > Ho           28 09.1     42 14.1    15 46.5     13 17.1   37 50.7
    >
    > GHA-A(:00)  206 53.2    206 53.2   206 53.2    206 53.2  206 53.2
    > GHA-A(inc)    3 53.1      4 16.2     4 45.8      4 57.1    5 03.8
    > SHA         258 43.0    158 41.8   234 22.5    278 43.3  194 04.0
    > Long        -54 00.0    -54 00.0   -54 00.0    -54 00.0  -54 00.0
    > ==========  ========    ========   ========    ========  ========
    > GHA-star    415 29.3    315 51.2   392 01.5    436 33.6  352 01.0
    >
    > Lat          11 00.0     11 00.0    11 00.0     11 00.0   11 00.0
    > Dec         -16 43.2    -11 09.8   -59 30.9      6 20.8   61 45.3
    >
    > Hc           28 32.3     40 51.1    14 56.3     14 21.0   38 54.8
    > Z              243.9       115.4      196.2       173.8     004.8
    >
    > Delta(dir)    23.2 A      83.0 T     50.2 T      64.0 A    65.3 A
    >
    > Plotting these gives a fix near 10 00.0 N and 53 00.0W. Reducing sights
    > again with A.P. of 10 N and 53 W:
    >
    > GHA-star    416 29.3    316 51.2   393 01.5    437 33.6  353 01.0
    > Lat          10 00.0     10 00.0    10 00.0     10 00.0   10 00.0
    > Dec         -16 43.2    -11 09.8   -59 30.9      6 20.8   61 45.3
    >
    > Hc           28 05.1     42 10.1    15 37.1     13 18.0   37 59.6
    > Z              244.8       115.1      196.7       274.2     004.2
    >
    > Delta          4.0 T       4.0 T      9.4 T       0.9 A    10.1 A
    >
    > Plotting these gives a good fix at about 9d 50.5'N  53d 00.0' W
    >
    > This is a bit far off course. What did I get wrong?
    My computed answer-- 9d 50.0'N 53d 00.2'W
    Don't see anything wrong. Your answers are within 0.5' of accuracy.
    > Every thing gets further askew from here on...
    >
    > > 2)  What is the TC and distance to Barbados(13d 10.0'N  59d 20.0'W)? --
    > > ----------------------------------------------------------------
    >
    > Hmmm ... isn't that a few miles east of Barbados?
    Yes. I am using approach positions given in Ocean Passages for the World
    and Cornell, World Cruising Routes. You don't want to run up on the
    island.
    >
    > Barbados  13 10.0            59 20.0
    > Fix      - 9 50.5          - 53 00.0
    >          ========           ========
    >  D.Lat =   3 19.5     D.Lo =  6 20.0
    >        =    199.5'         =   380.0'
    >
    > dmp = mp(13d 10.0') - mp(9d 50.5')
    >     = 202.3
    >
    > TC = 270 + arctan(202.3/380.0)
    >    = 270 + 28
    >    = 298d
    >
    > Dist = 199.5/sin 28
    >      = 424.5
    Very OK here.
    > > We continue sailing maintaining the same speed and True Course with an
    > > overcast sky. Then, with the navigator on deck waiting for an opening
    > > for a Sun shot, we see a spot of land on the horizon ahead. It is
    > > 20/05/2000 {at}XXX.XXX
    >
    > > 3)  What is the DR position?
    > > --  ------------------------
    >
    > S = 10.7 C = 288.9 T,
    >
    >   20/05/2000 12:13:00 ZT = 20/05/2000 16:13:00 UT
    >                           -18/05/2000 22:20:00 UT
    >                          ========================
    >                             1 day     17:53:00
    > or 41.88 hrs
    >
    > Dist = 41.88 * 10.7 = 448.1 nmi
    >
    > D.Lat = 448.1 * cos 288.7 = 145.2 = 2d 25.2'
    >
    > DR Lat = 9d 50.5' + 2d 25.2' = 12d 15.7'
    >  dmp = mp(12d 15.7') - mp(9d 50.5')
    >      = 147.0
    > D.Lo = 147.0 * tan(288.9)
    >      = -429.4
    >      = -7d 09.4
    > DR Lo = -53d  00.0 - 7d 09.4'
    >       = -60d 09.4
    >
    > DR  12d 15.7'N    60d 09.4'W
    >
    > Actually this is too far off to make any sense.
    > We seem to be well past Barbados.
    It is off. If you are calculating use a Traverse Table interpolation may
    be accumlating an error. A better method would be to use one of the
    Sailings methods for DR. For sight reduction at least using a Law of
    Cosines formula. If you insist on working it "longhand" download
    4mulas.zip from the web site.
    > > 4)  What day of the week is this?
    > > --  -----------------------------
    >
    > >From the almanac -- Saturday.
    Right
    > This I'm (almost) sure I have right :-)
     Your procedure seems OK. It may be the method you are using.
    Dan Hogan WA6PBY
    Catalina 27 "GACHA"
    dhhogan{at}XXX.XXX
    Navigation-L List Owner
    http://www.wa6pby.com
    

       
    Reply
    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