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    Re: SOA vs SMG
    From: Irv Haworth
    Date: 2009 Nov 4, 14:00 -0800

    Hello Joe..
    Sorry for confusion, but I did briefly cover this SOA vs. SMG in an earlier
    post. Given this I guess I'm taking a bit of a liberty in re-hashing the
    issue. Hopefully not too many members will take issue !
    Background: Basically I'm following the position of a large cruise ship,
    which has crossed the Pacific Ocean and is currently near Australia. This
    vessel like many others provide metrological data , wind speed, dir/ sea
    conditions etc. to the World Meteorological Org.(WMO) every few hours. At
    time of reporting it also (naturally) gives its position. ...say from point
    A (Lat and � )to point B. The speed of the vessel is stated as SOA ( which
    is the speed intended to be made good as you would do in plotting a DR
    track) In the reports the vessel submits (appears) to take the Rhumb line
    distance between position A and B which divided by the elapsed time interval
    to yield SOA, which they (system ?) reports.
    My contention is that the correct term to use is either SMG (speed made
    good- dist. between two positions divided by elapsed time ( a single
    resultant speed)) or SOG (speed over good...the speed from A to B).(recall
    the effects of wind dir, speed , whether she is sailing in a following seas
    More currently the "system" (computer-GPS or navigator ?) erred by suddenly
    reporting the ship in the wrong hemisphere resulting in a SOA of over 500
    kts.. then hours later corrected its self (got back on station) and reported
    a (SOA) speed of over 900 kts. 
    By means of an email I contacted the webmaster of the particular site, (ship
    positions)but despite being a former USN man was not able to offer any
    reasons . I then sent an email to a staff member (?) of WMO ,on or about 1
    Nov/09 but just rec'd an auto reply that he was out of office until Oct 15
    (presumably 2009...hi...hi). While I am retarded or is it retired ...I will
    try to sort this out before "slipping the lines:. 
    In a few words I also wonder just how this report was generated/approved
    and what .if any, correcting measures are in place at WMO to catch such
    errors.(WMO supplies ,free , to all ships which volunteer (VSO)to support
    their studies..this includes training).
    Hopefully this brings you up to speed (sorry but could not resist the
    temptation) And last the "plot' thickens..hi..hi
    Kind regards
    -----Original Message-----
    From: navlist@fer3.com [mailto:navlist@fer3.com] On Behalf
    Of joseph_schultz@rrv.net
    Sent: Tuesday, November 03, 2009 8:40 PM
    To: NavList@fer3.com
    Subject: [NavList 10418] Re: SOA vs SMG
    Hi Irv,
    Could be that thick-headed Joe doesn't understand your questions.  Ask away
    and perhaps others will answer better than I can.
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