A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Sextant development:was Re: Sextants in Little Rock
From: George Huxtable
Date: 2010 Jan 9, 10:35 -0000
From: George Huxtable
Date: 2010 Jan 9, 10:35 -0000
Henry (hch) raises several interesting points about sextant development. I wasn't aware that during the earlier years of World War 2, drum sextants were so hard to get, outside the military, in the US. How long before that did drum sextant manufature in the US start, then, and by which firm(s)? We can imagine why supplies were so short. Each new vessel would be replacing another that had been sunk by a U-boat, and gone down, most likely, with its navigators and their sextants. When he bought his Husun sextant in Glasgow during the war, was that a new instrument? I wonder if the sale of such sextants was then restricted, and whether Henry had to show any documents to buy it? Perhaps, in those days, his American accent was enough... It would be quite a feat of memory to recall such details, from 60-odd years back; unfair to ask, perhaps. And it's interesting to learn that after experience with both Vernier and drum instruments, Henry settled on a Vernier Plath, because of its superior optics. That, it seems, was more important to him than the easier-reading of the modern drum. The main trouble with a Vernier instrument, it seems to me (after very limited practical experience), is the difficulty in getting precise readings from the Vernier scale for twilight observations, particularly in poor lighting. Would there always be electric lighting available on the bridge in Henry's early days, or were some oil lamps still in use? I can remember a passage on a steam coaster, from Liverpool to Belgium, around 1950, in which all lighting was still by oil lamps. I am aware that bright lighting is to be avoided, to preserve night vision, but I wouldn't relish reading a Vernier under oil-light, even in the days when my eyes were much sharper than they are now. I remain puzzled by one aspect of the transition from Vernier to drum sextants. The first Plath drum instruments were in their catalogue from 1907. However, they didn't appear in the catalogues of Heath, or Hughes, until the late 1920s. Even if the Germans were ahead with their machine tools, I find it hard to explain the 20-year gap.Even if Plath had the patents sewn up, patents don't last that long, and German patent rights were unlikely to be given much respect during a World War. Were the new-fangled, foreign, drum instruments distrusted by non-German mariners? Was there any basis for such distrust? Were they eagerly accepted by German navigators? Did those early Plath drum instruments achieve the same precision as their Vernier counterparts? I wonder if opinions, around that time of the 1910s, can be found in pages of the nautical journals. Once Heath had introduced the "endless tangent screw" to their Vernier sextants, it might be imagined that they were most of way towards the drum sextant. All they had to do next, it seems, was to replace the simple knob by a graduated drum, and make the screw-pitch correspond to exactly 1 degree on the scale. That last requirement , however, called for extreme precision of both rack and worm. Was Heath's technology simply not up to the job? George. contact George Huxtable, at email@example.com or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. ----- Original Message ----- From: "hch"
To: Sent: Saturday, January 09, 2010 3:26 AM Subject: [NavList] Re: Sextants in Little Rock Hi Frank, I believe it safe to say that by the mid-1940s transition from vernier to micrometer drum sextants was well underway, if not actually completed. It as just that the micrometer drum sextants were not generally commercially available in the USA – certainly the military, both Allied and Axis, had them and they were being issued to new built merchant ships by the Maritime Administration, but over the counter sales were non-existent or, at least, very limited, thereby extending the life and availability of older vernier sextants which could still be found on the 2nd hand market The opposite situation prevailed in Great Britain where you could walk in and by a Husun “three ring” micrometer sextant over the counter most anytime after 1943, or thereabouts – IMHO this latter simple sextant contributed materially to the winning of the Battle of The Atlantic, and most Allied Seamen that I knew aspired to owning one. Micrometer sextants apparently were around, although not plentiful, since at least the 1920s, facilitated by the incorporation of the rack and pinion drive arrangement for movement of the index arm – I personally have never seen such an instrument without this drive arrangement, which was also incorporated into the vernier type sextant by Plath in later years, thus doing away entirely with the old style index arm clamp and friction fine adjustment arrangement in which the tangent screw could come “two blocks”. My first “sextant” was actually a John Bliss & Co. octant, purchased second hand (more likely third to fifth hand) at their establishment on Pearl Street in New York City in late 1943 – it was then probably in the order of 60 to 80 years old, had the old style index arm clamp and limited run friction fine adjustment device for a 15 second vernier, and was encrusted with a dark green coating of verdigris, making it a real “salty old dog”. Well sir, this old dog navigated me over a good part of the world and competed favorably in every day sights, including stars, with any modern sextant it came up against; it stared my lifelong affinity fort vernier sextants – I still have it today. Subsequently, I did join the crowd. While lying on the hook in the convoy anchorage off Gourock, Scotland, I got enough time off to catch the AM train to Glasgow, where the Winfred O. White establishment was located directly across from the Station, purchase a Husun “three ring” sextant for about $60.00, and return to my ship by way of the PM train. I have since owned and used German, Japanese, and British micrometer sextants of every description, but finally settled on a relatively simple Plath, certificated in 1946, fitted with a 10 second double spaced vernier, and endless tangent screw, i.e., rack and pinion drive. My preference for the Plath resides primarily in the telescope, which I simply find to be personally more comfortable in use. Sorry to offend those who don’t like sea stories, but you did ask. Regards, Henry --- On Fri, 1/8/10, FrankReed@HistoricalAtlas.com wrote: From: FrankReed@HistoricalAtlas.com Subject: [NavList] Re: Sextants in Little Rock To: NavList@fer3.com Date: Friday, January 8, 2010, 11:27 AM Henry, you wrote: "The term "endless tangent screw sextant" was a common expression for the sextant sub-type possessing such a device, prior to the common usage of the endless or geared tangent screw - it it recognized as a sextant sub-type by definition in HO 220."So then, circa 1940-45, it still would have been "new enough" that a sextant would specifically have been referred to as "endless tangent screw" as a novelty? Was your first sextant a micrometer sextant? And was this distinct from an "endless tangent screw" sextant? Or were all micrometer sextants also "endless tangent screw" sextants?You added: "The abbreviation ETS is not, however, a recognized or, at least, defined abbreviation except in the imagination of the originator. Today, folks seem to make up abbreviations as they go along and everybody else is expected to understand - apparently a requirement of the electronic age. "This bugs the hell out of me, too. It's the era of acronyms. Linguists say it started around 1925. Before then, you will almost never find acronyms (famously, this is one of the reasons why you can be sure that "POSH" was not an abbreviation for "port out, starboard home" as in the popular 'folk etymology'). Acronyms are now everywhere. But it's not going to change, so I guess we better "learn to love and live with acronyms" -- a policy which I call "LLLWA" or in print "L3WA" (so there's no misunderstanding... I am kidding).-FER ---------------------------------------------------------------- NavList message boards and member settings: www.fer3.com/NavList Members may optionally receive posts by email. To cancel email delivery, send a message to NoMail[at]fer3.com ----------------------------------------------------------------