NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Coastal Plotting Sheets
From: Michael Bradley
Date: 2007 Mar 26, 17:58 +0100
From: Michael Bradley
Date: 2007 Mar 26, 17:58 +0100
Peter P F wrote: 'What this coastal nav course proposed was taking the same three corrected bearings but plotting from the fix position onto clear material from a point on the plastic sheet representing the side opposite to the land � the seaward side. So three position lines radiating outwards.' I left it a week, but no-one else has jumped in. Regardless of the tool used for the plotting, such as 'clear sheet', a station pointer, or a Douglas Protractor, what has been suggested to you in that technique is downright dangerous. There are two reasons for this. From three LOPs gained from the hand bearing compass, suitably corrected, plotted normally, you produce on the plot a cocked hat which warns by its size if one of the LOPS is inaccurate. If you use the horizontal sextant angle station pointer type method of plotting that same data, it does not indicate any error, it just generates an apparently ambiguity free dot on the plot which is almost certainly wrong. Furthermore, the horizontal sextant angle station pointer type method itself is notorious for a poor angle of cut built into its geometry, particularly if the 'middle' object sighted is further away than the two 'side' objects sighted. Don't be tempted by what you've been told - a tidy plot is not the same thing as an useful plot. Michael Bradley ___________________________________________________________ All New Yahoo! Mail � Tired of unwanted email come-ons? Let our SpamGuard protect you. http://uk.docs.yahoo.com/nowyoucan.html --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---