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 77
    From: Michael Wescott
    Date: 2001 Jul 25, 8:29 PM

    > Promptly at Sunrise on 24/06/2001 we raise anchor at Isl Flamenco
    > (08d 55.2'N  79d 31.6'W) and head for our departure point at Isla
    > San Jose Light(08d 10,5'N  79d 31.6'W) motoring.
    
    Is Isla San Jose Light truly due south of our anchorage?
    
    > Speed = SQRT LWL x 1.34
    
    > 1)  What is the Zone Time (ZT) of our Estimated Time of Arrival(ETA)
    >     at the Isla San Jose Light?
    
    >     What is the UT/GMT ETA?
    > --  ----------------------------------------------------------------
    Sunrise at Isl Flamenco should be:
            0541 (Almanac entry for 10d N)
            +  2 (Interpolation for Latitude)
            + 18 (4d 31.6'west of center of zone)
            ====
            0601
    
    Speed is 1.34 sqrt(39) = 8.4 kn
    
    Dist = 44.7 mi (by inspection)
    
    Time en route = 44.7/8.4 = 5.32 hr (5h 19m)
    
    ETA = 1120 ZT (GMT-5)
        = 1620 UTC
    
    
    > On our ETA at Isla San Jose we take a departure FIX off of the light that is
    > (08d 55.2'N  079d 29.4'W). We set our course for the Mid-Ocean Point(MOP) at
    > (03d 00.0'N  110d 00.0'W).
    
    Been motoring in circles, have we? We're only a couple of miles from
    our anchorage.
    
    > Variation 2.0dW, Dev 0.5dE. Drift 0.6 Kts Set 285.0d. Speed 10.1 Kts.
    
    > 2)  What is the TC and Distance from Isla San Jose Light to the MOP?
    > --  ----------------------------------------------------------------
    
    dLat = 355.2'
    dLo = 1830.6'
    dep = dLo * cos 6 = 1820.6
    arctan(355.2/1820.6) = 11d
    sqrt(355.2^2 + 1820.6^2) = 1854.9
    
    C=259T, D=1854.9
    
    > We plot our track on INT Chart 811 and see that we can not head direct for
    > the MOP(03d 00.0'N  110d 00.0'W) without crossing land above Punta Mala in
    > Panama. So we alter course to MOP2 at (05d 00.0'N  80d 00.0'W).
    
    > Variation 2.0dW, Dev 0.5dE. Drift 0.6 Kts Set 285.0d. Speed 10.1 Kts.
    
    > 3)  What is the True Course and distance to MOP2?
    >     What is the Compass Course(CC)/Course-to-Steer?
    > --  -----------------------------------------------
    
    Assuming the course changed at 08d 55.2'N  079d 29.4'W, i.e. immediately.
    
    dLat = 235.2
    dLo = 30.6
    dep = 30.6 * cos 7 = 30.4
    arctan (235.2/30.4) = 82.6
    sqrt (30.4^2 + 235.2^2) = 237.2
    
    D = 237.2
    C = 187.4T = 189.4M = 188.9C
    
    Correcting for current (plotting sheet)
    
    C = 184T = 186M = 185.5C
    
    
    > At 14:45:30UT the next morning we take a SUN LL sight. Other Data as above.
    
    >     Hs 47d 54.6''
    
    > 4)  What is the DR position?
    > --  ------------------------
    dTime = 2400 + 1445 - 1620 = 2225 = 22.4 hr
    D = 10.1 * 22.4 = 226.24
    
    dLat = cos 187.4 * 226.24 = 224.4'S
    dep = sin 187.4 * 226.24 = 29.1 mi W
    dLo = 29.1/cos 7 = 29.3'W
    DR = 5d 10.8'N  79d 58.7'W
    
    > At 22:45:23UT we take another sight of the SUN LL
    
    >     Hs 15d 34.3'
    
    > 5)  What is the DR position?
    > --  ------------------------
    dTime = 2245 - 1445 = 8hrs
    D = 10.1 * 8 = 80.8 mi
    dLat =  cos 187.4 * 80.8 = 80.1'S
    dep = sin 187.4 * 80.8 = 10.4 mi W
    dLo = 10.4/cos 4.5 = 10.4'W
    
    DR = 3d 50.7'N    80d 09.6'W
    
    > 6)  What is the Running FIX(RFIX) position at the 22:35:23UT sight?
    > --  ---------------------------------------------------------------
    
    Which is wrong, this time or the  22:45:23 above?
    
    At 22:35:23, I get a Ho = 12d 31.7' at the DR.
    At 22:45:23, I get a Ho = 10d 14.0' at the DR.
    
    Something is way off. Was the time actually 22:25:23?
    
    > Checking our Running FIX against the position of MOP2(05d 00.0'N  080d
    > 00.0'W) it seems we have passed MOP2. So we alter course to our original Mid-
    > Ocean Point which we re-name MOP1(03d 00.0'N  110d 00.0'W).
    
    > Speed 10.5 Kts. Current Set 285, Drift 0.6 Kts. Var 1dW Dev 2dE.
    
    > 7)  What is the TC and Dist to the MOP1(03d 00.0'N  110d 00.0'W)?
    >     What is the Compass Course(CC)/Course-to-Steer?
    > --  -------------------------------------------------------------
    
    Form DR 3d 50.7'N    80d 09.6'W to MOP1:
    
    dLat = 50.7'
    dLo = 29d 50.4' = 1790.4
    dep = 1790.4 * cos 3.5 = 1787.1
    arctan(50.7/1787.1) = 1.6
    
    C = 268.4T = 269.4M = 267.4C
    D = sqrt(1787.1^2 + 50.7^2) = 1787.8
    
    Correcting for current (plotting sheet):
    
    C = 267T = 268M = 266C
    

       
    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