A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Jeremy C
Date: 2011 Jun 20, 11:53 -0400
On November 30 last year, in Navlist post number 14566, George Huxtable made some kind comments about my book "The Nautical Sextant", and concluded his remarks by writing:
"Bill makes no pretense to be anything other than a landsman. I
would love to take him to sea, as a shipmate in a small craft in brisk
weather, with a few sextants to try out, to discover whether his
assessments survive that school of hard knocks."
I have a daughter and three grandchildren living near Houston in Texas and my wife and I try to visit them about once a year, so largely in response to George's challenge, instead of flying direct to Houston from Auckland, I booked a passage on the M.V. Natalie Schulte from Auckland to Oakland via Papeete (Tahiti) and Ensenada (Mexico), departing mid April this year. Although I have handled many types of sextants, most of my observations have been made on dry land, using a sea horizon where available and an artificial horizon when it was not. We have a 14 ft fishing dinghy and occasionally I have taken sun shots from it with results within 2 miles of my position as determined by transits (ranges in American), but the voyage was an opportunity to do some concentrated celestial navigation.
I had a choice of over forty sextants, and decided to take my favourite, an SNO-T, equipped with a 6 x 30 prismatic monocular by Beck Kassel, borrowed from a 1953 C Plath sextant. I was not sure whether the ship would in these times have a nautical almanac, so I took my own, and a scientific calculator completed the outfit. In the event, the ship had two completely unused Freiberger Trommel sextants, an almanac, a full set of marine and aeronautical sight reduction tables and pilots for various parts of the world. However, none of these was ever used, as there were duplicated GPS systems, each with battery backup power and two independent radar systems, again with battery backup. However, the course was plotted on paper charts and the position, derived from GPS was plotted hourly. The clocks that looked like chronometers turned out, on closer examination, to have the same movement as my kitchen clock at home. I never saw anyone use the gyro repeaters on the bridge wings, though I was shown their alidades, but of course there was no need, as pilots guided the ship in and out of the various ports. On a couple of occasions, one of the GPS units refused to work, so the mates and the Electrical Officer puzzled over the innards with the aid of a very fat manual written in English rather than their native Russian.
My approach was to take sights, solve the astronomical triangle with the help of the calculator and use the GPS position as the assumed position, correcting for the ship's motion (usually at 20 kt), so that the intercept directly gave me an indication of how well I was doing. There weren't really any surprises as I made all the mistakes I had anticipated making: taking the GHA and declination from the wrong page of the opening of the almanac, misreading the watch time by a minute, taking GHA Aries instead of that of Venus and failing to remember on one occasion that the longitude, while of a similar magnitude, had changed from East to West. At least I had no difficulty with the time and date, as I set my watch to UT and left it there for the whole voyage. I had bought a cheap digital watch with internal lighting, that I fastened to the rear end of the sextant with some Velcro, but in practice I found it much easier and quicker to take the time straight off my analogue wrist watch and in practice found that it took me about a second to do so.
Again, at first I wrote down the results in a small notebook and this meant that I had awkwardly to set down the sextant on the deck to do so. I had experimentally glued a plastic note tablet to the handle of the sextant (see posed attachment) and quickly found that this was much easier to use, as it meant that I had simply to slip my left hand beneath the handle and steady the heel of my right hand against the finger tips of my left in order to make notes in soft pencil. In this way, I was able to make an observation single handed in less than a minute, provided that the clouds cooperated. One of the other passengers said that he had been a Fleet Navigator in the US Navy when young. Though he was not especially talkative about the subject of navigation, he did tell me that on his ship, three people took sights simultaneously and they had a writer to take down their results.
According to a retired sea captain friend, in days gone by the height of eye on the bridge was always placarded somewhere. If it was placarded on the bridge of my ship, I could not find it and the officers were not able to tell me either, so I took a series of nine careful sun sights, noting the GPS position at the beginning and the end of the series. By this means, I was able to work back to the height of my eye on the bridge wing, together with an unknown amount of "personal equation." This gave me a height of 20 metres that I was later able to adjust to 24 metres when I discovered a scale drawing of the ship in the corridor leading to the ship's office.
I very soon discovered that instrumental error was unimportant compared to the effects of a poor or false horizon. When the horizon was clear, an average of five sun shots generally gave me an intercept of less than an mile, increasing to up to three miles when it was indistinct. On one occasion, when it was impossible to say quite where the horizon lay, the intercept was 21 miles, unimportant in the middle of the Pacific Ocean, but critical if expecting to come upon land. Formerly, of course, the navigator would be able to assess the goodness of his celestial navigation only at departure and landfall, at other times relying on large discrepancies between his observed and calculated position to warn him of error. Captain Kryachko, the only officer to have had practical experience of celestial navigation, said that he became suspicious when the discrepancy exceeded ten miles and found an error of three miles perfectly normal and acceptable.
Star shots gave me disappointing results as most mornings the skies were either completely overcast or the stars darted in and out of view in patchy overcast. As often as not, the horizon was indistinct until only the brightest stars and Venus remained for observation. As I was not familiar with the northern constellations and they were in any case seldom fully visible, I made a polar diagram of their bearings and altitudes to lay across the wing compasses, but even so, some results were so preposterous that it was plain I had misidentified the body. Astern, the ships funnel gasses had sometimes a disconcerting effect on the observations. When I correctly identified the body, the intercepts varied from less than a mile with a good horizon to nine miles with an indistinct one, with most clustered around four or five miles.
Before I set out, someone, I think it might have been Jeremy (Anabasis75), remarked on Navlist that I should have a stable platform for observations on a medium sized container ship. I certainly anticipated that it would be so, as the ships length was 207 metres, its beam nearly 30 metres and its displacement was 33,400 tonnes, with a maximum draught of 11.40 metres. There is, of course, a "however" : on the Auckland to Tahiti leg of the voyage the top containers, loaded with produce and goods for Tahiti, were necessarily on top. This resulted in a small metacentric height, roughly speaking the distance between the centre of mass and the centre of bouyancy. I think the Chief Mate mentioned a figure of 0.96 metres, which is about 3 percent of the beam. The effect of a small metacentric height is to make the vessel very "tender", that is to say it rolls a lot but slowly, no bad thing one might think, as the opposite case, where the ship is "stiff", it makes short, sharp rolls, which can be quite damaging to cargo.
In the South Pacific, the length of swells varies between 180 and 300 metres, similar to the ship's length. As we quartered the swell on the way to Tahiti, the ship rolled up to 12 degrees, taking over 20 seconds to complete a cycle, the meanwhile pitching occasionally as the swell and the ship's period seemed to coincide. On one particular morning all the officers were complaining about the discomfort of the rolling having prevented them from sleeping, as their bunks, like mine, were fore and aft, and the Captain averred that he was going to sleep on his (athwartships) couch that night. The behaviour of the ship meant that it was not easy for this tyro navigator to manage his sights. I had at times to wedge myself into a corner of the bridge wing in order to stay upright. When moving from one wing to the other it was inconvenient to undog heavy doors and in any case, if the opposite door was already open, the wind threatened to send paperwork flying, so my route lay behind the funnel, with only a railing between me and a fall five decks below to the poop deck. I was very careful! After Tahiti, where only empty containers were loaded, the ship's motion was much more comfortable.
The wind could cause me other problems too. At 20 knots and sometimes heading into a 30 knot wind, gusts would sometimes whip into the corner where I had wedged myself and threaten to tear the sextant away from my face or to bump it against my eye socket. Old salts may tut tut and say that it serves me right for preferring an aluminium sextant, but at nearly 2 kg, with the monocular, the SNO-T is no lightweight. When heading into the wind, a surprising amount of spray found its way up to the bridge. Sometimes it was obvious, when the ship dipped its bows into a swell, but even when it was not obvious to the senses, it showed itself as a fine encrustation of salt on the mirrors and on my spectacles. I always took care to inspect the mirrors and to wash off the salt with a swab soaked in fresh water.
As to what to do with spectacles, I did consider Bruce Bauer's suggestion of leaving out one lens of a spare pair, so that one could look through the scope through one eye without a lens and view the reading of the instrument and watch with the other eye aided by a lens. If you keep your spectacles on, you lose a lot of the field of view and this can make stars hard to find and, once found, to bring them down to the horizon. I found it much easier to whip the specs off and grip one arm ("temporal" to opticians) between my teeth, as I have enough residual vision without the glasses to be able to see objects close-to.
Though my primary purpose was to practice celestial navigation, the voyage was interesting on several other counts: I got to see the workings of a large ship and how it was loaded and unloaded; I had a guided tour of the engine room by the Chief Engineer and was then allowed to wander around on my own to take photographs with the admonishment to "be very careful"; passengers were allowed free entry to the bridge at any time as long as they did not interfere with the ship's working (the main interest of some of them seemed to be in the coffee machine). The captain, a Ukrainian in his mid-forties was unfailingly friendly, polite and helpful and treated his Filipino crew with kindness and respect. The other officers were also friendly and, within the limitations of language (Russian, Spanish and Filipino), chatty and helpful.
To others who might be contemplating a similiar voyage I would recommend it as an experience. You should not expect cordon bleu food, but will find it plentiful and wholesome, nor should you expect the crew to act as your servants, so if you don't know how to make up a bunk or keep your cabin tidy, get some lessons beforehand. It was not a cheap exercise, costing about 110 Euros a day, so I could have flown twice from Auckland to Houston and back for what I paid for the one way voyage. I would gladly repeat the experience - if someone else pays!
Finally, many thanks for many things to George Huxtable.
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