NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Chronometers
From: Henry Halboth
Date: 2008 Mar 29, 11:21 -0700
From: Henry Halboth
Date: 2008 Mar 29, 11:21 -0700
Hi Alex, Although these references do not contain technical details on chronometer construction, you will find more information in the various editions of Dutton's Navigation texts. The later edition of 1985 broaches the subject of Quartz Chronometers ... "capable of maintaining an excellent rate, with the better models having a deviation of less than 0.01 seconds from their average daily rate that should not exceed 0.2 seconds per day. Many models have a sweep second hand that can be advanced or retarded electronically in increments of 1/10 or 1/100 second while the chronometer is running." These instruments are battery operated, thus obviating the need for winding. This edition also broaches the use of atomic clocks for ultra-accurate navigational systems and missile guidance purposes, however, does not go into detail. I have used the commercial models of the so-called "atomic" clocks for sight purposes ashore and have found them to be satisfactory, but have no personal experience in their use at sea; I seem to recall having read that these commercially available time pieces are accurate to only withing 4-seconds, however, am unable to quote a reference. Older editions of Dutton, specifically that of 1934, which was my initial navigation text, details the older 20th century methods and procedures as followed by the US Navy. At that time well run ships, with presumably well heeled owners, carried at least two, if not three chronometers, and there was advocated a method of Chronometer comparison whereby the regularity of of daily rate could be demonstrated - using three chronometers it is possible to identify the chronometer whose rate has changed, while with two chronometers it is possible only to identify that the rate has changed. This comparison procedure of course presumes that a time signal is not regularly available; it is a boring procedure which at one time we had to learn. There are other texts that include commentary on the chronometer, Bowditch, Norie and Mixter being three that come immediately to mind, however, none that go into technical detail as to construction. To obtain any detailed specifics as to construction one would necessarily have to refer to watchmaking manuals, some of which deal in great detail with the chronometer and the methods of its manufacture. To increase the accuracy of reading the 1/2 second beat, I have sometimes used a 1/100 second reading mechanical stop watch running simultaneously with and synchronized with the chronometer second hand. Regards, Henry --- Alexandre E Eremenkowrote: > > > Henry, > Thank you for your interesting information. > > > I suppose there might be some argument with > respect to > > methodology if the time between determination of > > errors was particularly great, > > Strangely enough, I do not find any instructions on > determining the chronometer rate in the navigation > manuals that I have. > > I would imagine the following procedure (before the > use of radio). While a ship is in a harbor, the > correction > would be determined daily by the time signals > (gun shots, falling ball). From this the daily rate > will > be derived. And then used until the next harbor with > time > signals. > > > daily rate of 1.5 seconds losing. From a practical > > Very close to my chronometer: my one is loosing 1.37 > sec > per day so far, and this is constant within a > second. > > Here is a difficulty by the way: how do I determine > the correction with say 1/2 second accuracy? > The chronolmeter clicks and shows every 1/2 second. > But my electronic watch (and Internet) clicks with > only 1 second frequency, so errors of comparison are > sometimes more than 1/2 second. > > > point of view, it was customary to request a new > > chronometer be set slow so that the error be > additive > > -I guess true sailors didn't subtract too well. > > That's a very good point! > Now I know why my chronometer is 1.2 sec slow:-) > > By the way the factory certificate I have contains a > lot > of information from which I can infer how they were > tested. > I can post the details if there is interest. > > I cannot repeat this test because it involvs > five 5-days periods > running under given constant temperature:-) > > Alex. > > > > > > ____________________________________________________________________________________ Like movies? Here's a limited-time offer: Blockbuster Total Access for one month at no cost. http://tc.deals.yahoo.com/tc/blockbuster/text4.com --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---