NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: How Many Chronometers?
From: Frank Reed
Date: 2009 May 11, 00:06 -0700
From: Frank Reed
Date: 2009 May 11, 00:06 -0700
Jeremy Allen, you wrote: "I've used the Stark Lunar tables with good results. As long as you know the hour and a decent DR, you can use the tables to determine GMT via Lunars to the accuracy of your shooting ability. They take a while to reduce the sight however." There is nothing "special" about Bruce's lunar tables except (and this exception is important!) the fact that they were published by him at a time when lunars were almost unknown to practical navigators. He almost single-handedly re-introduced lunars back in the 1990s. Apart from that, the tables offer no particular benefit, though they are certainly very clever. From the early 19th century onward, there was a mis-conception among many commentators on navigation proposing that the problem with lunars, and the reason that they were not used more often, was the difficulty of the math. This was reputation, not reality. While there were some poor tables published, any of the common methods available worked very well and did not entail significantly different levels of mathematical skill or effort. You also asked: "What I wonder is what ships did in the age of steam before the age of common time ticks (say the early part of the 20th century). I haven't seen any ships with more than 2 chronometers on it, but my shipping experience is relatively short. When I worked with chronometers, we kept an error and rate log. The chronometers were serviced periodically and reset at that point. Nothwithstanding the early age of chronometers, what was the time solution in a more modern age? Does anyone have any data on this?" Just the things that have already been mentioned. Time balls and other signals in many ports which were frequently provided by synchronizing with a local observatory. Spotting a known headland, even a tiny island, with a known longitude. Speaking other ships was also extremely common. And in the age of radio (in the few years before the official time signals) speaking other ships by radio extended the range of this time-honored method from a few hundred yards to hundreds of miles. "What time is it?" (meaning GMT usually) was such an important and common question that it was assigned a Morse shorthand at a very early date. Gary Lapook told the list back in October of 2007 that the signal was "QTR". But just so we're clear, the real solution was multiple chronometers. The other checks are rarely necessary when you have a set to compare one against the other. -FER --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---