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    Re: SOA vs SMG
    From: Joe Schultz
    Date: 2009 Nov 5, 02:59 -0800

    Hi Irv,
    I think I get it.  Here's how the US Navy trained me, pertaining to surface vessels:
    
    SOA = speed of advance.  Labeled with letter "S" prefix on the dead reckoning 
    (DR) track.  The planned speed through the water, ignoring anything that 
    would affect the vessel, such as wind or current.
    
    SMG = speed made good.  Calculated from fix to fix, using the fix time 
    interval divided into the distance between fixes.  The AVERAGE speed over 
    ground, as the vessel can change direction and speed up or slow down at any 
    point between fixes.
    
    SOG = speed over ground.  Considered an INSTANTANEOUS speed for a surface 
    vessel, and was usually only used when planning a DR track.  Say, for 
    example, the speed limit in a traffic separation scheme is 12 kts and we 
    determine that we'll have a following current of 4 kts.  We'll then plan for 
    a SOA of 12 - 4 = 8 kts in order to have a SOG of 12 kts.
    
    The Navy owned the ships so they had the final say in what the words were and 
    what they meant.  "Your way, the right way or, if you like your pay, the Navy 
    way."
    
    WMO runs their program so they have the final say as to what the words mean.  
    Looks to me, from the US handbook that I refered to earlier, that WMO and US 
    Navy agree on the definition of SMG.
    
    If I was a betting man (not more than a friendly cup of coffee) then I'd say 
    that the web site you're referring to (sailwx.com ??) is downloading batch 
    files from WMO, then doing a bit of computer processing before you see what 
    you see.  They own their web site so they get to say what the words mean, 
    regardless of the confusion they may create.
    
    As a department head on my second ship I had message release authority.  If I 
    signed it then the radiomen sent it.  I signed for exactly one mistake in two 
    years on that ship, a mistake small enough that I can't remember what it was. 
     But you'd think the sky had fallen - I remember that.  Your cruise ship made 
    (and corrected) a small mistake in the scheme of things - don't sweat it.
    
    Keep us posted on your communications with these folks.  I like my coffee hot, 
    black, and with a pinch of salt.
    
    Joe
    
    
    
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