NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Sight Reduction method accuracy
From: Henry Halboth
Date: 2004 Apr 4, 15:34 -0400
From: Henry Halboth
Date: 2004 Apr 4, 15:34 -0400
Thought I might add something regarding the comparative accuracy of the various sight reduction methods spoken of here from time to time. Over the years, I have experimented under all conditions at sea with most methods, at least through HO 249 - specifically this is meant to include the Longitude Time Sight, Marc St. Hillaire, Ageton, Dreisenstok, Martelli, several British Admiralty methods, HO 214, and HO 249 - and never found any significant discrepancy as respects positions found, with the possible exception of HO 249 in the use of which "rounding off" errors seemed to tend to multiply and result in more than the usual number of "cocked hats". As a matter of convenience, especially in cramped small vessel navigation, I favored Dreisenstok (HO 208) over most other methods and could match speed of calculation, as well as accuracy, with most any other method - for pre-computation of altitude and azimuth, I found HO 249 a handy accessory tool. I became at one time enamored with (and still am) Martelli's Tables which constitute one of the first short tabular methods for solution of the Longitude Time Sight, although in recalculating, I have found several errors or misprints in my copy. These tables are simple and easy to use, and with a little manipulation can serve for intercept calculation. Unfortunately they do not provide for the computation of azimuth, for which other tables or formulae must be employed. As respects the age old discussion of utilizing a DR position, as opposed to an assumed position, in any intercept method, there never seemed to be any significant or practical difference in positions established by whatever method was used. This of course does not refer to utilization of the Time Sight solely for longitude, in which case an accurate Latitude must be employed - the more so as the body moves out of the prime vertical toward the meridian. Someday I will share with you my experience with Lunar Distance observations at sea, which date back to the 1940's before the apparent current renewal of interest. Regards. Henry