NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: SOA vs SMG
From: Irv Haworth
Date: 2009 Nov 4, 14:00 -0800
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 etc) 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 Irv -----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. Joe --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList+@fer3.com -~----------~----~----~----~------~----~------~--~---