Keeping Track of a Maiden Voyage

¹ In 1880 the legal time for Great Britain was made Greenwich Mean Time (GMT) by Act of Parliament. In the same act the legal time for all of Ireland was made Dublin Mean Time (DMT) and was not changed till 1916 to be the same as GMT. Dublin is at longitude 6° 15' W, which meant that DMT was 25 minutes behind GMT. [For a more detailed history of events up to this point, see Derek Howse, Greenwich Time and the Longitude (National Maritime Museum / Philip Wilson Publishers, 1997).] However, according to the rules and regulations of the International Mercantile Marine Company (owners of the White Star Line) that were in effect in 1912, departure and arrival times when entering or leaving English or Irish waters were always to be recorded in GMT. Once out to sea, time was kept according to where the ship would be at local apparent noon, the instant of time when the true sun would reach its highest point in the sky. Time being kept this way was known as Apparent Time Ship or ATS. When arriving or departing points in the United States or Canada, ship’s time would be changed to the mean time for the 75^th meridian of longitude which was exactly 5 hours behind GMT.

² A Great Circle track is the path you would get if you took a tightly stretched string and used it to connect any two points on a globe. It is the shortest distance that connects those two points.

³ A rhumb line track is the path that you would get by following a fixed compass direction without change. If the compass direction you followed was due north or due south, you would also be following a great circle track on one of the earth’s meridians. You would also be on a great circle track if you happened to be on the earth’s equator and went due east or due west. Any other direction to the north or south of due east or due west will eventually spiral in toward one of the earth’s poles.

⁴ This route was known as the southern track taken by steamers heading westbound across the Atlantic leaving Queenstown. It was in effect from January 15^th through August 23^rd. The point called “the corner” marked the end of the great circle part of the westbound voyage. Eastbound steamers on the southern track would reach a corner point 60 nautical miles to the south of the westbound corner point before they would take to the great circle part of their eastbound voyage. From August 24^th through January 14^th these routes were shifted northward by about 120 nautical miles, and were know as the northern track. A voyage taken on the northern track made the passage across the Atlantic about 110 nautical miles shorter. After the Titanic disaster the southern tracks were shifted further southward.

⁵ The Daunt’s Rock light vessel was located at 51° 43’ N, 08° 16’ W from 1905-1938. (Ref: “A Directory of Hydrographic and Atmospheric Datasets for the North East Atlantic and UK Shelf Seas,” Science Series Tech. Report No. 113, Centre for Environmental, Fisheries and Aquaculture Science, 2001, App. 1 – MAFF Coastal Sea Temperature Stations.) The location of the rock itself is at 51° 43’ 30’’ N, 08° 17’ 30’’ W (Ref: www.traveljournals.net).

⁶ We take the turning point to be about 3.3 miles south of the Old Head of Kinsale lighthouse. The lighthouse itself is located on the coast at 51°36.3' N, 8°31.9' W (Ref: The Commissioners of Irish Lights at www.cil.ie).

⁷ Fastnet lighthouse itself is precisely located on a rock island at 51º 23.3’ N, 09º 36.1’ W (Ref: The Commissioners of Irish Lights at www.cil.ie).

⁸ Following the Olympic’s second voyage of 1911, we will take this point to be about 2 miles south of the Nantucket Shoals light vessel. The light vessel itself was listed in the US Coast Pilot Part III for 1912 at 40° 37’ 05’’ N, 69° 36’ 33’’ W.

⁹ The Ambrose Channel light vessel was listed in the US Coast Pilot Part IV for 1909 at 40° 28’ 02’’ N, 73° 50’ 01’’ W. Before passing Ambrose the ship would also pass the Fire Island light vessel located at 40° 28’ 40’’ N, 73° 11’ 26’’ W. But it was the Ambrose Channel light vessel that marked the end of the Atlantic crossing and entrance to lower NY harbor.

¹⁰ Although there were several errors in the memorandum submitted by Pitman, the distances provided for each day’s run can be confirmed from other testimonies and sources. (See American Inquiry, pages 420-421.)

¹¹ Confirmation of the run for Day 1 of 484 miles comes from testimony of J. Bruce Ismay.

¹² Confirmation of the run for Day 2 of 519 miles comes from Ismay and 2^nd class passenger Lawrence Beesely. In his book, The Loss of the SS Titanic, Beesley wrote that the purser had mentioned to him that the 519 mile run for day 2 was a disappointment.

¹³ Confirmation of the run for Day 3 of 546 miles comes from Ismay, and passengers Lawrence Beesley, Henry Stengel and Archibald Gracie.

¹⁴ Photographs of the Old Head of Kinsale and Fastnet lighthouses presented in this article are by permission of Philip Plisson (www plisson com).

¹⁵ Although the course of the ship was usually set at noon each day, it appears that the Titanic’s course was changed about 5 hours 36 minutes past LAN (which was at 1:24 PM GMT) on the 12^th of April. This 7:00 PM GMT position, which was transmitted from the Titanic to the La Touraine at 7:45 PM GMT, is about 6 miles north of the great circle track at the reported longitude. It is interesting to note that in the log of Olympic’s second voyage to New York (in July 1911), the last two out of three noontime positions along the great circle part of her route were 10 and 8 miles to the north of the great circle track line, respectively. Additionally, the first noontime position for the part of Olympic’s route from the Corner to the Nantucket Shoals light vessel was 6 miles to the north of the rhumb line track that she was to be on.

¹⁶ From testimony given by the Titanic’s 5^th Officer Harold Lowe (American Inquiry, p. 381), the course from noon to the corner was 240.6° true, and the distance was 126 nautical miles (after correcting what appears to be a transposition error of two digits in the transcript of his testimony). Working back from the Corner at 42° N, 47° W, and going 126 nautical miles along the reciprocal heading (060.6° true) gets us to a noon position of 43° 02’ N, 44° 31’ W. This position is a total distance run of 1549 miles from Daunt’s Rock over the course that was traveled.

¹⁷ Since the Earth makes one complete rotation with respect to the sun in 24 hours, and since there are 360 degrees in a complete rotation, each 15 degree change in longitude corresponds to an hour change in time. Traveling westward, for example, you would need to reset your clock back by 1 hour for every 15 degree change in longitude that you make. However, this 24 hour day that we are all so used to is measured with respect to a fictitious sun called the mean sun. The earth’s rotation with respect to the true sun, also called the apparent sun, is not exactly 24 hours. This difference arises from two separate causes. The first is that the plane of the equator is not the same as the plane of the earth's orbit around the sun, but is offset from it by the angle of obliquity, the tilt of the earth’s poles. The second is that the orbit of the earth around the sun is an ellipse and not a circle, and the apparent motion of the sun is not exactly equal throughout the year but appears to be moving fastest when the earth is closest to the sun. Even standing on the prime meridian at Greenwich, this difference can cause the true sun to be overhead several minutes before or several minutes after the clock strikes 12:00 PM GMT, depending on the time of the year. This difference is what is called the Equation of Time and must be added or subtracted from the mean time when calculating local apparent noon for any point on the surface of the earth.

¹⁸ Rhumb line distances shown here are based on a mid-latitude calculation method for a spherical earth. One minute of arc in latitude is equal to one nautical mile.

¹⁹ Rounded off to the nearest degree.

²⁰ Samuel Halpern, “A Minute of Time,” THS Commutator, Vol. 29, No. 171 and 172, 2005.

²¹ Although the clocks were adjusted the night before to read 12:00 for local apparent noon the next day, a minor adjustment up to a minute if needed was made in the forenoon when they obtained a more accurate longitude for their noontime position (American Inquiry, p. 294.) If the Titanic’s clocks were adjusted back by 25 minutes the night before her arrival at Queenstown to Dublin Mean Time (which was kept throughout Ireland in 1912) as some people have suggested, then the total clock setback (including adjustment in the forenoon) for the first day out from Queenstown would have been 59 minutes. There is some indirect evidence that suggests that the clocks might have been set back about 58 minutes at midnight during the first night’s run since departing Queenstown as this number appeared in a memorandum prepared and submitted by 3^rd Officer Pitman to the American Inquiry (pp. 420-421). That memorandum had in it the distances run for each day and the departure time at Daunt’s Rock. As pointed out before, departure times in English and Irish waters were always recorded in GMT by White Star Line rules. A 2:20 PM GMT departure can also be check against the speed she was making carrying 70 revolutions per minute. Other setback times in that memo, however, can be shown to be completely unreliable, and cannot be verified by any other available evidence.

²² American Inquiry, page 451.

²³ American Inquiry, page 294.

²⁴ The time interval from LAN one day to LAN the next day is just 24 hours plus the amount of time the clocks were set back. This hold for all days except the first day out. Because they took departure in the afternoon at 2:20 PM GMT off the Daunt’s Rock light vessel, the time of the first day’s run is 24 hours minus the difference between their departure time in GMT on April 11 and the time of LAN in GMT on April 12. That difference was 2:20 – 1:24 = 0:56. Therefore 56 minutes from 24 hours leaves 23 hours and 4 minutes, the time interval from departure at the Daunt’s Rock light vessel on April 11 to local apparent noon on April 12.

²⁵ Speed over ground is not the same as speed through the water. Ground speed is the vector addition of speed through the water plus the net affect of current and wind.

²⁶ American Inquiry, page 3.

²⁷ British Inquiry, 965.

²⁸ Samuel Halpern, “A Minute of Time,” THS Commutator, Vol. 29, No. 171 and 172, 2005.

²⁹ British Inquiry, 17608.