by David Barrie
4 R. Ch. Duval, “Admiral Marcq de Blond de St. Hilaire,” Journal of Navigation, vol. 19 (1966) 209–12.
5 Cotter (1968) 293ff.
6 The exact steps are as follows: First draw a line through the assumed position along the bearing of the computed azimuth. Then compare the observed altitude with the computed altitude; if the observed altitude is greater than the computed one it follows that your actual position is closer to the GP of the observed body than the assumed one—and vice versa. Then convert the difference in altitude into a distance in nautical miles (this is called the “intercept”—one minute of arc equaling one nautical mile), and mark this on the azimuth line, either toward or away from the GP. At this point draw a line at right angles to the azimuth line. This represents a tiny segment of one of the equal-altitude circles discussed earlier, and you are somewhere on it: it is a “line of position.”
7 C. H. Cotter, “A Centennial Tribute to Marcq St. Hilaire,” Journal of Navigation, vol. 28 (1975) 449ff.
8 Real professionals (like hydrographers) need also to know the biases that they bring to the task of taking a sight. Most of us cannot, even with long practice and in ideal circumstances, measure a sextant angle (or record the exact time of a sight) with complete accuracy, and our errors tend to follow a pattern. Once these biases are known, they can be allowed for by applying a “personal equation” to the sights we take.
9 Quoted in Cotter (1968) 306
10 The merchant service was much slower to adopt it, however, long remaining faithful to the old “longitude by chronometer” method.
11 Lecky 462.
12 Wolff 79–80.
13 Ibid. 93–94.
14 Ibid. 96–97.
15 Ibid. 97–98.
16 Ibid. 100–111.
17 Slocum 22.
18 Ibid. 15.
19 Ibid. 24.
20 Ibid. 96.
21 Ibid. 98–99.
22 Ibid. 100.
23 Ibid. 101–102.
24 South America Pilot II.167.
25 Slocum 102.
26 FitzRoy III.307.
27 Slocum 102.
28 Ibid. 142.
29 Ibid. 144–45.
30 Ibid. 146–47.
31 Ibid. 148.
32 Ibid. 149.
33 Bowditch iv, 233.
34 Wolff 206–209.
CHAPTER 16: ENDURANCE
1 Thomson 22.
2 Thomson 37.
3 Shackleton 7.
4 Ibid. 32–33.
5 Ibid. 39.
6 Ibid. 52.
7 Ibid. 57.
8 Ibid. 63.
9 Ibid. 67.
10 Ibid. 71–72.
11 Ibid. 72.
12 Ibid. 79–80.
13 Ibid. 81.
14 Ibid. 82.
15 Ibid. 83.
16 Worsley 24.
17 Ibid. 25.
18 Ibid. 27.
19 Ibid. 30.
20 Ibid. 32–33.
21 Ibid. 41.
22 Ibid. 44–45.
23 Ibid. 46–47.
24 Ibid. 50.
25 Ibid. 54–55.
CHAPTER 17: “THESE ARE MEN”
1 Worsley 60–61.
2 Ibid. 62.
3 Shackleton 174.
4 Worsley 64.
5 Shackleton 181.
6 Worsley 67–68.
7 Ibid. 82.
8 Ibid. 74–75.
9 Ibid. 86.
10 Ibid. 88.
11 Ibid. 92.
12 Ibid. 93–94.
13 Ibid. 95–99.
14 Ibid. 120.
15 Ibid. 125–26.
16 Ibid. 128–29.
17 Ibid. 139–41.
18 Ibid. 145.
19 Ibid. 144–46.
20 However, the members of Shackleton’s expedition who were sent ahead to establish a depot for him on the other side of the Antarctic did not fare so well. Two men died and four others only narrowly survived: see Shackleton 265–66.
21 FitzRoy I.557–58.
22 See Lewis 1994. David Lewis was an intrepid single-handed sailor, and his account of the navigational skills of the Pacific islanders is full of fascinating details.
23 Lewis 313ff.
24 Quoted in ibid. 176.
25 Ibid. 280ff.
26 Ibid. 127.
27 Comparable skills are exercised by the Inuit in the northern Canadian Arctic. Relying on close observation of a complex array of natural cues, including stars, winds, snowdrifts, tides and animal behavior, they can find their way across wide expanses of sea, ice, and land with complete confidence—in almost all weather conditions. But it takes years of “quiet tutoring and experience” to gain these skills, and there are concerns that increasing reliance on GPS will erode them. See Claudio Aporta and Eric Higgs, “Satellite Culture: Global Positioning Systems, Inuit Wayfinding, and the Need for a New Account of Technology” in Current Anthropology, vol. 46, issue 5, December 2005, 729–53.
28 The Polynesian Voyaging Society, for example. See their website: http://hokulea.org/vision-mission.
29 See, for example, Gooley; Huth.
30 See Gooley. 158ff.
CHAPTER 18: TWO LANDFALLS
1 Howse 111–12.
2 Ruskin V.370–71.
3 Conrad 2.
EPILOGUE
1 See Edward M. Lassiter and Bradford Parkinson, “The Operational Status of NAVSTAR/GPS,” Journal of Navigation, vol. 30, issue 01, January 1977, 3–47.
2 Solar pressure alone can displace a satellite by almost 40 meters each day.
3 Strictly speaking, spheres, since GPS operates in three dimensions.
4 Modern estimates of the accuracy of celestial fixes obtained at sea suggest that an error radius of about two nautical miles is to be expected—if the observer is experienced, the conditions are good, the time is precisely known, and the sextant is reliable. (See, e.g., N.L.A. Bovens, “Position Accuracy of Celestial Fixes,” Journal of Navigation, vol. 47, issue 02, May 1994, 214–20.) Multiple observations at a fixed point on land can, however, reduce this to a few hundred yards.
5 For a much fuller discussion of the vulnerabilities of GPS and other satellite navigation systems, see Dr. Wolfgang Schuster, “Protecting the Future,” Navigation News, The Magazine of the Royal Institute of Navigation (September–October 2013) 22–24.
6 “Ships’ navigators go back to the future as white van man gets them into a jam,” Times, March 30, 2013.
7 New Scientist, December 12, 2012.
8 Matthew Crawford has written very interestingly about this subject—though in a slightly different context. See Crawford esp. 59–61.
9 For an interesting overview of this subject, see Alex Hutchinson’s article “Global Impositioning Systems—Is GPS technology actually harming our sense of direction?” in Walrus, November 2009 (http://thewalrus.ca/global-impositioning-systems/). See also Nicholas Carr, “All Can Be Lost: The Risk of Putting Our Knowledge in the Hands of Machines,” in Atlantic, November 2013 (http://www.theatlantic.com/magazine/archive/2013/11/the-great-forgetting/309516/).
Glossary
Azimuth: the bearing of a celestial body’s geographical position measured in degrees either from the north or south pole (whichever is nearer the observer).
Beam: the width of a ship at her widest part; also a term for the transverse members on which a ship’s deck is laid.
Beam ends: A ship is on her beam ends when she is heeled over by ninety degrees.
Binnacle: the housing for the steering compass, which usually includes a small lamp.
Bosun’s chair: a board on which someone can be hoisted aloft to carry out repairs or inspect the rigging.
Broach-to: A vessel running before a strong wind broaches to when the helmsman loses control and she turns sharply to windward. She may then be “knocked down” by the pressure of the wind in her sails.
Cable: a distance of two hundred yards.
Careen: heaving a ship over onto her sid
e to expose her bottom for purposes of repair or maintenance.
Chains (or “cheans”): a small platform on either side of a ship from which the lead-line is heaved.
Cockpit: a well in the deck of boat—usually close to the stern and uncovered—from which she is steered, either by tiller or by wheel.
Declination: the angle of a heavenly body north or south of the equator as measured from the center of the earth.
Embayed: A sailing vessel is embayed when blown by onshore winds into a bay from which it cannot escape by tacking.
Fathom: six feet.
Genoa: a very large triangular sail set on the main forestay of a yacht.
Geographical position: the point on the earth’s surface vertically beneath a heavenly body.
Great circle: a circle on the surface of the earth that has its center at the center of the earth. The equator is one example, and all meridians are parts of great circles.
Greenwich Hour Angle: the angle between the Greenwich meridian and the meridian over which a heavenly body is passing at any given moment.
Jib: a generic term for triangular sails set on a forestay of a ship or yacht.
Larboard: the old term for “port” (as opposed to “starboard”).
Lead-line: a specially marked rope to which is attached a lead weight for measuring the depth of water and for taking samples of the sea bottom (using a bit of sticky grease or tallow).
Leeward: downwind, as opposed to upwind or “windward.” Hence lee shore.
Local Hour Angle: the angle between the observer’s meridian and the meridian over which a heavenly body is passing at any given moment.
Log: any device for measuring a ship’s speed through the water. The traditional “chip log” consisted of a weighted, wooden quadrant that, when thrown overboard, pulled out a carefully measured “log-line” marked—literally—with “knots.” By counting the number of “knots” that passed in a given interval of time (usually determined by the “log glass”) it was possible to estimate the vessel’s speed in “knots” or nautical miles per hour.
LORAN: short for LOng RAnge Navigation, a radio-based navigation system developed in the United States during the World War II for military purposes. By measuring the time intervals between pulsed transmissions from shore-based radio stations, it is possible to fix a ship’s position on a special chart. An enhanced form known as E-LORAN is being developed as a backup to GPS.
Main (or mainsail): the principal sail of any sailing vessel. In most yachts it is attached to the mainmast and extended by a long horizontal spar known as the “boom.”
Meridian: half of a great circle joining the north and south geographical poles, otherwise known as a line of longitude.
Nautical mile: the length of one minute of arc of a great circle at the earth’s surface, or approximately 6,080 feet. It is 15 percent longer than a statute mile.
North: true north marks the direction of the geographical north pole; magnetic north marks the direction of the magnetic north pole.
Offing: a safe distance offshore, avoiding all dangers.
Paying off: The bows of a sailing vessel “pay off” when they have passed through the eye of the wind and start to drop off to leeward, typically when tacking.
Quarter: The after part of a ship is divided into two quadrants on either side of the midline—the port and starboard quarters. Hence quarter gallery: a small gallery on each quarter of a ship connecting with the stern cabin often accommodating a lavatory, and quarterdeck, the after part of the upper deck of a ship, usually reserved for the captain and officers.
Schooner: typically a two-masted sailing vessel in which the foremast is lower than the mainmast.
Scuttle (or “Skuttel”): a circular port or window in the side of a ship, commonly called a porthole.
Shrouds: the fixed (or “standing”) rigging used to support the mast of a ship laterally. The “stays” by contrast provide fore and aft support.
Staysail: a triangular sail set on one or more of the forestays of a ship or yacht.
Steerage: a large cabin below the quarterdeck and just forward of the great cabin.
Stream anchor: a spare anchor, often deployed from the stern of a ship.
Tacking: the process of bringing the bows of a sailing vessel up into the wind and then allowing the sails to fill on the other side or “tack” when going to windward.
Tender: a small vessel serving in support of a larger one.
Tiller: a long bar attached to the head of the rudder by means of which a boat is steered. Larger vessels are steered with wheels.
Tonnage: Originally a measure of cargo capacity, a ship’s tonnage was estimated in the days of sail by a formula taking into account the length and breadth (“beam”) and depth (“draft”) of a vessel. This is not a measure of the weight of a vessel, which is known as its “displacement.”
Whaleboat: a rudderless open boat, propelled by oars and pointed at both ends. Modelled on those used for hunting whales, they were steered with an oar and could easily be beached. They were particularly useful in coastal survey work.
Yard: a spar on which sails are carried; in a square-rigged ship the yards cross the masts horizontally.
Yawl: a two-masted sailing boat in which the smaller, after mast (or “mizen”) is mounted (or “stepped”) very close to the stern.
Zenith: the point in the sky vertically above the observer.
Zenith distance: the angular distance between a heavenly body and the observer’s zenith.
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