NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: The Noon Fix
From: Ralph Clampitt
Date: 2009 Apr 8, 13:49 -0800
From: Ralph Clampitt
Date: 2009 Apr 8, 13:49 -0800
Just like to add, as a list follower, that this kind of thread is of great interest to those amateurs among us. I will be crewing for my son-in-law in a few weeks for an off shore passage from San Francisco to San Diego and will use this as an opportunity to work on my noon sights while probably running mostly downhill, North to South. I've ordered Jim's book from Amazon. Thanks, RC S/V Wayfinder -----Original Message----- From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Hewitt Schlereth Sent: Wednesday, April 08, 2009 1:30 PM To: NavList@fer3.com Subject: [NavList 7885] Re: The Noon Fix Frank, here's a second to your remarks re Jim's method. Jim, your book sounds very apt for today's realities - Celestial is bound to be in the 'if all else failz' category. I'm off to Amazon to buy a copy. Hewitt On 4/8/09, frankreed@historicalatlas.comwrote: > > Jim, you wrote: > " It is not a running fix, since no lines of position are advanced or retarded. Or even determined." > > > If you're adjusting the sights for motion of the observer, that is equivalent to a running fix. So unless you're explicitly reserving the expression "running fix" for the case of plotted LOPs, I don't think there's any problem calling it a running fix, and that may be helpful explaining the method to navigators who already understand that concept. > > This whole business of generating a fix by a series of sights around noon is a subset of a general case which I have labeled (in the absence of previous terminology) a "rapid fire fix". If you take a series of multiple Sun sights, oner after another, over a fairly short time interval so that the Sun's azimuth changes by a moderate amount (let's say twenty degrees), then you can reduce these sights, perform a least squares analysis, and get a fix that is surprisingly accurate. This is a type of running fix since each sight has to be advanced/retarded based on the observer's motion. > > In a general "rapid fire fix", the position is clearly more accurate in the direction of the Sun's azimuth just as the particular case of sights around noon yields a latitude that is more accurate than the corresponding longitude. The accuracy in the perpendicular direction is lower but increases rapidly either by multiplying the number of sights or by allowing for a larger change in azimuth. > > -FER > > > > > > > > --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---