NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: ex-meridian sights - further question
From: Steven Wepster
Date: 2001 Feb 14, 7:13 AM
From: Steven Wepster
Date: 2001 Feb 14, 7:13 AM
Most interesting. The Ex meridian method stems from ancient times before the good Marc. Ste. Hilaire position line method. However it appears to be time honoured especially with DOT examiners. What has always interested me is why not simply use a sight taken 10 or so minutes before or after noon ( up to 30 or so minutes allowed by ex-merid tables) as a simple P/L. It can be used with future or past P/L's to give a position. Historically the idea of the ex-merid. was that commercially it was most important to have a noon position so that distance run and distance to go was known and course fuel consumed, slip and the rest of it calculated. Commercially of course the noon pos. is still important although usually worked from GPS. I dont want to knock the users of the ex. merid. its just that I have never had a use for it. Regards Barrie Actually the ex-meridian latitude was invented by the Dutch teacher Cornelis Douwes in the 1740s, ie before the steam-driven steel vessels. The method was considered very useful because those were the days before accurate chronometers were available for use at sea, there was no notion of an altitude line of position, and Marc St Hilaire wasn't even born yet. The ex-meridian method allows the navigator to obtain a latitude fix on days when it is quite cloudy and the sun just visible for a few seconds close to, but not at, local noon. _Steven.