Encyclopedia Titanica

True Course

An explanation of the use of magnetic compasses, how to plot courses and how these procedures on the Titanic compared to their use other ships in 1912


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The use of magnetic compasses, how to plot courses and how these procedures on the Titanic compared to their use other ships in 1912 is something of a mystery to many observers. Yet an clear understanding of the equipment and procedures is crucial to correctly interpret testimony in the American and British Inquires. This article shall endeavour to clarify the issues.

True Course

A ship’s true course is determined by the direction from the ship to the geographic north pole (also called true north).Navigation charts andthe compass are labeled with true north, but setting a ship’s course is not merely a matter of steering in relation to the north pole. The magnetic compasses, like those on Titanic, point to the earth’s magnetic poles. Unfortunately the magnetic poles move around with time and do not line up with the earth’s geographic poles. Currently the North Magnetic Pole is just north west of Baffin Island in Canada and the South Magnetic Pole is just north of Australia. In 1912 navigators relied on magnetic compasses so they had to calculate the difference between magentic north and true north in order to determine a ship’s true course.

Magnetic Compasses

Magnetic compasses have existed since the 11th century, according to article 111 of Bowditch’s American Practical Navigator, 1995 Edition (2). They function because a magnetized needle floating freely will line up with the earth’s magnetic field, which lines up with the earth’s magnetic poles. The difference between true north and magentic north is called compass error. There are two kinds: variation, the difference between magnetic north and true north, and deviation, which is caused when the steel of the ship affects the magnetic compass. Both kinds of compass error must be taken into account when calculating a ship’s course.


Variation is the difference between the direction from a ship to geographic north and from a ship to magnetic north. It is named East or West depending on the ship’s position relative to these two poles.In theNorth AtlanticOcean variation is westerly, because when looking towards the North Pole, the North Magnetic Pole is to theleftof the North GeographicPole. Refer to Fig. 1Illustration of Variation. If a ship’s position were directly in line with both these poles then there wouldn’t be any variation.

Figure 1 Illustration of Variation (by R. Pundt)

The amount and name of the variation in any location can be picked off the chart for that area. Because the magnetic poles are always moving, variation changes from year to year. The amount of variation is indicated on navigation charts each year. Refer to Fig. 2 Charting Variation.

Figure 2 Charting Variation (NOAA Chart 13288)

Variation can not be corrected, but must be taken into account when figuring the actual course to steer. To compensate for variation one adds the value of the variation to the true course to get the magnetic course.

Capt. Lord testified on the 7th day of the British Inquiry that the Variation in the area of the sinking at that time was 24 degrees W (question 6782).


The other error found in a magnetic compass is called Deviation, which is caused by ferrous metal in close proximity to the compass. Deviation wasn’t a problem until the advent of iron and steel ships. Because the amount of steel varies, deviation varies from ship to ship, and from one magnetic heading to another.

There are a couple of ways to reduce deviation error when calculating what course to steer. First, one can reduce the amount of steel in close proximity to the compass so it will give the most accurate reading. This is why ships like Titanic had a compass on the top deck, away from the steel of the ship. That compass was called the Standard Magnetic Compass. Refer to Fig 3 Magnetic Compass in its Binnacle and Fig. 4 Close Up of Magnetic Compass with Azimuth Circle. The other magnetic compasses onboard (such as the Steering Magnetic Compass in the Wheelhouse) were checked against it.

Figure 3 Magnetic Compass in its binnacle (Photo by C. Weeks).
Magnets go in the open door. The red and green iron spheres are Quadrant al Correctors. The magnets and Quadrantal Correctors correct for deviation.

Figure 4 Close Up of Magnetic Compass with Azimuth Circle (Photo by C. Weeks). The sun light is reflected off the mirror on the right intothe prism on the left which bends it down onto the compass card. Note the thin light line on the compass card, that indicates the bearing of the sun.

Second, a compass adjuster could, while swinging the ship on shoreside range marks, as depicted in Fig. 5 Shoreside Range Marks, arrange magnets and soft iron spheres around the compass to offset the effects of the ship’s structure, then note the residual error (remaining deviation) when he was finished.


He then made a chart (Deviation Card) of this residual error, which was posted in the chartroom or wheelhouse so that the appropriate value could be picked off and used in figuring the course to steer by applying the deviation from the Magnetic Compass heading.

Capt. Lord testified onthe 7th day of the BritishInquiry thatthe Variation in the area of the sinking at that time was 24 degrees W, with a Deviation of 2E, making a [compass] error of 22W (question 6782). 24W – 2E = 22W.

As an example of how Deviation varies from ship to ship, notice that Californian’s Deviation was 2E; Titanic’s was 1E.

Applying Variation and Devation

Courses laid down on navigation charts are labeled by their true heading, that is, their heading as regards Geographic (True) North. This is also represented by the meridians printed on the chart and the outer ring on the compass rose (refer to Figure 2 Charting Variation). By applying Variation, True plus Variation, one gets what is called the Magnetic Course (True adjusted for Variation). This would be the compass course in a vessel that had no metal in it.

Next, one applies Deviation to the Magnetic Course to get the Compass Course, i.e., Magnetic with Deviation applied. This is the heading on the magnetic compass that indicates a certain Geographic heading on the chart.

For a chart to calculate Variation and Deviation, refer to Figure 8 Titanic's Variation and Deviation Matrix.

Titanic’s Compass and Procedures

Standard procedure on Titanic was for the junior officer on watch to measure the sun’s azimuth bearing on the standard compass once per watch. This measurement was compared to the calculated bearing to determine compass error.

According to the International Mercantile Marine’s 1907 company book of regulations, captains were to “steady the ship on her course by standard [compass] every half hour, and must compare the compasses every Watch” (253). That meant the senior officer on watch had to compare the Standard Magnetic Compass (the most accurate) to the Steering Magnetic Compass every four hours.

Because Titanic’s Standard Magnetic Compass was on a raised platform between the second and third funnels, comparing it to the Steering Magnetic Compass in wheelhouse was not easy. Refer to Fig. 6 Titanic's Boat Deck, which shows the distance from the magnetic compass to the bridge (approximately 230 feet). The officer had to walk to the compass platform and indicate when the course was correct by pulling a bell which would ring in the wheelhouse. When the helmsman heard the bell, he knew the ship was on True Course and noted what course to steer on the Steering Magnetic Compass to maintain that course.

This procedure was not only very tedious and rife for error, but may have played a part in events on Titanic just before the accident by drawing an officer and spare helmsman away from the bridge where they could have been watching for ice.


Figure 6 Titanic's Boat Deck (Photo by C. Weeks) The distance from the compass platform to the bridge is approximately 230 feet.

The compass arrangement on Olympic class ships was different from other ships which had the Standard Magnetic Compass on the top of the Wheelhouse, fairly convenient to the Wheelhouse. Refer to Fig. 6 Titanic’s Boat Deck, which shows the distance from the compass platform to the bridge, and Fig 7 Titanic and Lusitania, which shows Lusitania’s magnetic compass on the flying bridge and Titanic’s magnetic compass platform between the second and third funnels.

Figure 7 Titanic and Lusitania (Photo by C. Weeks) Lusitania’s Magnetic Compass on the Flying Bridge (between brown barrels). Compare to Titanic, behind Lusitania. Also compare to Fig. 6.

Navigation After 1912

Just before World War I the gyroscopic compass appeared on the scene. The gyro compass is an electro mechanical device which basically functions like a gyroscopic top. When spinning and lined up with the meridian it holds that position regardless how the the ship moves around. It is not affected by deviation and variation and there is only one error, called gyro error. It is determined periodically by use of shoreside ranges or bearings of celestial bodies. These bearings are called Azimuths or, in special circumstances, Amplitudes. In either case one must compare the bearing as observed against the bearing as calculated. The difference is the gyro error. It is named East or West and has an amount, usually less than a degree. Thus the gyro compass comes closest to indicating Geographic North.

The RoyalNavy Battle cruisers,HMSInvincible andthe HMSInflexible had gyro compasses in December of 1914 when they fought at the Falklands; however, due to cost, most merchant ships did not have gyro compasses until after World War II.

Unfortunately, Titanic didn’t have a gyro compass, only magnetic compasses. As a matter of fact, in addition to the Standard Magnetic Compass she had three Steering Magnetic Compasses: one in the Wheelhouse, one on the Captain’s Bridge, and one at the Emergency Steering Station on the After Docking Bridge. It needs to be understood that a more accurate compass would not necessarily have prevented the accident, which was primarily caused by not seeing the iceberg in time to avoid it.

More recently the use of GPS (Global Positioning System) has taken over for the compass. Because GPS receives fixes so frequently and compares them to the direction to the next waypoint it effectively shows what direction to head in. When hitched up to the steering control it will alter the ship’s heading to be headed towards that next waypoint automatically. This is what most modern ships do, although the officers do know how to correct True Course to Compass Course.

Modern Courses vs. Quadrant Courses

In 1912 Quadrant Named Courses were used; now 360 degree courses are used. Readers who are familiar with 360 degree courses might not understand the testimony of Titanic’s surviving officers regarding her course.

For example, in questions 13498 – 13501 of the British Inquiry Second Officer Lightoller said Titanic’s True Course was S 86 W, and that corresponded to N 71 W per the steering compass.

Quadrant Named Courses named their course first, fromNorth (000 degrees) or South (180 degrees), then East or West

Quadrant CourseConversion360 Degree Course
N 45 E000 + 45045
S 45 E180 – 45135
S 45 W180 + 45225

Therefore, Lightoller’s S 86 W is 180 + 86 = 266 degrees, so Titanic’s officers were steering 289 on the steering compass to make 266 true.

When a mariner wants to convert the True Course on the chart to his compass courses he uses a matrix like this to calculate the algebraic sum of deviation and variation:

W+   W-
-->   <--

Figure 8 Titanic'sVariation and Deviation Matrix (calculated by C. Weeks)

The top line of figures is the course before the course change at the “The Corner” (Lat. 42 N, Long. 47 W, where Titanic altered course from a Great Circle to head directly toNY); thesecond lineis from after The Corner. The headings across the top indicate:

True The course laid down on the chart

Var. Variation

Magnetic Magnetic = True plus Variation

Dev. Deviation

Compass The Steering Magnetic Compass (directly in front of the Helmsman) = Magnetic minus Deviation

Compass is what Titanic’s officers were actuallysteering. Compass error is the algebraic sum of deviation and variation. Specifically:

266 (Standard Magnetic Compass = True plus Variation)
- 265 (Steering Magnetic Compass = Magnetic minus Deviation)
1 East (Titanic’s Deviation)

To summarize, in orderto understand the testimony of Titanic’s deck officers, readers need to understand the difference between the Steering Magnetic Compass and the Standard Magnetic Compass, how to account for Variation and Deviation, and the difference between Quadrant Named Courses and 360 degree courses.


Bowditch, Nathaniel. American Practical Navigator: an Epitome of Navigation. Washington: Defense Mapping Agency Hydrographic Center, 1995. Internatiional Mercantile Marine Company. Ship's Rules and Uniform Regulations. Issued July 1st, 1907. “Chart 13288: Monhegan Island to Cape Elizabeth.” Washington: NationalOceanographic and Atmospheric Administration, Aug. 17, 1985. Pundt, Ralph, Capt. Assistant Professor of Marine Transportation and Nautical Science. “Illustration of Variation.” Maine Maritime Academy. Castine, MA, Sept. 8, 2003. “Wreck Commissioners' Court Proceedings.” Titanic Inquiry Project. Rob Ottmers, ed. Copyright © 1999-2002: Titanic Inquiry Project. 5 Sept. 2003

© Cathy Akers-Jordon & Captain Charles Weeks 2003-12-06 Accepted for Publication 9 December 2003

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  1. David G. Brown

    David G. Brown said:

    This paper is a succinct discussion of compass navigation in the 1912 era. As such, it is "must" reading for anyone trying to de-mystify the various courses and headings given in the testimonies. However, this paper has a much more important aspect. Under the heading "Titanic's Compass and Procedures," it contains the underlying cause of the accident. Titanic's fatal flaw was not brittle steel nor sulfur inclusions in the rivets. The fatal flaw had nothing to do with bulkheads or watertight doors. Titanic's sinking was the direct result of the design of the ship's bridge with regard to the standard compass. More than a year ago, Captain Erik Wood and I were able to deduce that Titanic was involved in a maneuver of some sort at the time of the accident. It was only when Nate Robison placed a copy of the IMM handbook in our hands that we found proof of our supposition. Based on the requirements for the ship to be steadied every half hour on the standard compass, it is

  2. Bill Wormstedt

    Bill Wormstedt said:

    David - forgive my confusion. Where was Wilde was all this was going on? I don't recall if at some point you thought he was also on the bridge, or if I ran across this comment elsewhere. How did Murdoch 'turn over' control of the bridge to Boxhall, if Boxhall was back at the compass?

  3. David G. Brown

    David G. Brown said:

    Bill -- Wilde was off duty and (presumably) in his room at the time of the accident. He played no role in events until immediately following the iceberg. Your question about "turning over command" is right on the money. The man doing the steadying of the ship on the standard compass worked from the platform. (At 11:30 p.m. that would have been Boxhall.) A one-way bell pull was used to signal the wheelhouse to turn left or right until the ship was on the specified course. Then, another signal would synchronize a "hack" of the compass readings. The wheelhouse compass would always be different from the standard compass, but things were OK as long as the difference remained the same (assuming the heading did not change). During the process of steadying on the standard compass all helm instructions came from the platform. For practical purposes, the officer on the platform was conning the ship even though he had no view of dangers forward. Quite obviously, the senior

  4. Bill Wormstedt

    Bill Wormstedt said:

    Thanks for the explanation, David. Would they still have done this, *if* they had know they were in amongst the icebergs? My wondering where I heard that Wilde was on the bridge during the collision, may be just confusion. I though I had read it in Stormer's newer Murdoch bio, but checking, I see she thinks Capt. Smith was on the bridge, but I can't find anything about Wilde.

  5. David G. Brown

    David G. Brown said:

    Bill -- Captain Smith was "on the bridge" per Boxhall's testimony. In particular, Boxhall said that the captain never left the square defined by the two chart rooms, the wheelhouse and the forebridge between when he returned from dinner and the accident. Further, Boxhall stated that the captain was beside him in the forebridge so quickly that the berg could not have been past the docking bridge after the accident. Wilde appears to have come onto the bridge voluntarily almost immediately after the accident. There is virtually no direct testimony about his actions, only "ghost" information. He was forward on the forecastle very quickly after the accident, investigating air hissing out of a vent pipe, etc. It would appear that he took it upon himself to do a physical examination of the ship. This is the probable explanation of why Boxhall's first trip forward was focused upon the condition of the 3rd class passengers. There was no need for two officers to do the same work, yet

  6. Bill Wormstedt

    Bill Wormstedt said:

    No argument about Boxhall's statements about Smith. Keep this up, and I may be seeing you in Maine!

  7. monica e. hall

    monica e. hall said:

    "Captain Smith was "on the bridge" per Boxhall's testimony. In particular, Boxhall said that the captain never left the square defined by the two chart rooms, the wheelhouse and the forebridge between when he returned from dinner and the accident. Further, Boxhall stated that the captain was beside him in the forebridge so quickly that the berg could not have been past the docking bridge after the accident." Now I'm confused. If Boxhall was away aft, doing his stuff with the compass, how does he know where Capt. Smith is just before the accident?

  8. David G. Brown

    David G. Brown said:

    Monica-- excellent question. Boxhall had seen the captain on the bridge at various times during the time period in question. In fact, the two worked closely on navigational matters. Naturally, while on the compass platform Boxhall could not have known the captain's whereabouts. That's why his comments about the captain being next to him immediately following the iceberg are important. The timing indicates that Smith could not have been farther away than the officer's chartroom at the moment of impact, which supports Boxhall's general statements about the captain's whereabouts. There are other bits and pieces of information which corroborate this. A correct interpretation of Hichens' testimony indicates the captain went through the wheelhouse just as the ship was touching the ice. And, the timing of the ALL STOP engine orders on both telegraph systems is strong evidence the captain was on the bridge for that event. It took the four hands of two men to operate both systems.

  9. monica e. hall

    monica e. hall said:

    OK, David, got that. Even more confused now - if there are no survivors from the bridge area except Hitchens, and he says the Capt. passed through the wheelhouse just as the ship was touching ice, then where on earth did the idea come from that Smith was asleep (not that it matters that much IMO in blame terms - skippers do have to sleep after all...) Sleeping captains seems to be a bit of a motif in the whole business.

  10. monica e. hall

    monica e. hall said:

    Don't answer that - me being stupid. Lightoller, of course, when they completed their discussions about sea conditions during his watch earlier. So if what you are saying is correct, nobody actually knows the exact responsibility for orders/actions on the bridge. How much could Hitchens see / hear from the wheelhouse? Seems odd the Capt. passing through the wheelhouse (from which direction?) as it was 'just touching ice' as per your interpretation of Hitchens's evidence. Surely he would have heard and felt the effects of Moody's manoeuvre before that (telegraph clanging, vibration etc.), like so many others, and shot onto the bridge as soon as he did if he were awake, and therefore been there during the 30-something seconds while they waited for the ship to turn?

  11. David G. Brown

    David G. Brown said:

    Monica -- you are probing right into the heart of the matter. In fact, you are dangerously close to discovering the "heart" of my new book. The 3-strokes on the lookouts bell would not hve caused any concern for Captain Smith. It was a normal event for the lookouts to report dangers around the ship--that was their job. Smith would certainly have noted the sound, but not taken any action. Responding to a report by the lookouts was Murdoch's job. By the way, the lookouts did not "warn" the bridge of the iceberg. Rather, they reported a sighting dead ahead. I make this observation because modern readers tend to believe the lookouts were pre-computer warning buzzers. They were not to warn the officer of the deck, just to report any sightings. In 1912 it was the officer's job to warn himself by keeping a sharp lookout. My conclusion from reading the testimony is that Murdoch was probably aware of the berg before the lookouts sounded their report. The thing that would have

  12. Erik Wood

    Erik Wood said:

    I was unprepared for the emails I got regarding Dave's posting, but let me add and repeat that he and I agree on the subject as a whole. The problem with recontructing an event of this type after 90+ years is that all the key players are gone. There are several key questions that do not add up. Those questions have be repeated over and over and don't need to be repeated here. Captain Week's event in Maine will be the highlight of a about 4 years worth of research. I would be happy to and have answered all questions that I have recieved and I most definitly look forward to the coming debate.

  13. monica e. hall

    monica e. hall said:

    David, well, I certainly don't want to pre-empt your new book! I've actually bothered to read Hitchen's' testimony to both Inquiries since your last post, and I agree it is rather at odds with the given ideas. I also have to say that Lord Mersey's attempts to clarify things to his mind unfortunately has the effect of obscuring issues to mine. He seems to have got on the Attorney General's nerves a bit too. Seems to me the Capt. was somewhere to the rear of Hitchens, but really cannot have been asleep. Also there seems far less time between events than popularly suggested - 3 bells, followed almost immediately by simultaneous hard-a-starboard and the crushing noise, and then it stopped, and the Capt. being there during the crushing noise. Of course, people's estimates of time during crises is often unreliable. And H. says a crushing noise, not a scraping one, but you've dealt with that one before haven't you? Thinking it over, I think Lord Mersey simply didn't ask the right

  14. Parks Stephenson

    Parks Stephenson said:

    Unfortunately, I have to finish one project before I can move to another. The timing of my current project is such that I can't attend the meeting in Maine, much as I would like to. I have some distinct problems with the scenario played out here. First of all, let me state that I share Dave's belief that Smith was not asleep and that the telegraph bells are probably what first caught his attention. I also share in the belief that Murdoch was probably the first to see the berg and that Titanic's compass platform was not in the best location. I do not, however, see justification in the testimony for the claim that Boxhall was in the compass platform just before the accident. I think we can all agree that Boxhall was away from the bridge on appointed rounds about that time and it could be that he was on the platform at some point to help calibrate the steering compass. But there's not a hint of his being on the platform during the critical time discussed here in either his

  15. David Haisman

    David Haisman said:

    Re David Brown and others. ''The three rings on the Lookouts Bell would not have caused any concern to Captain Smith '' Totally wrong! ''It was a normal event for Lookouts to report dangers around the ship- That was their job.'' Wrong again! ''Smith would have certainly noted the sound, but not taken any action'' Wrong again! ''Lookouts did not warn the bridge of the iceberg'' Comment: Dear Old Fred Fleet would have liked to have heard that one! ''Lookouts were not to warn the officer on the bridge?/deck? to report any sightings'' Really! ''Murdoch was aware of the berg before the Lookouts'' Well I'm buggered! Finally, for anyone to rely on Hitchens,no more than a glorified AB on navigational expertise reveals just how little is understood on the bridge of a British Merchantman Over to you ''book worms'' and testimony digesters! I look forward to some salient and experienced comments, David

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