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Message |
    
Jim Currie
Member
Username: sailorjim
Post Number: 429
Registered: 4-2008
| | Posted on Sunday, May 24, 2009 - 4:30 pm: | 
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Afternoon Sam,
Of course I have! (ideas that is).
The time of 1750 to alter course was entered by Smith into the Captain's Night Order Book. (I think.
As I've said before; Smith had a very bad but unfortunately very common (then as now) habit of keeping his subordinates in the dark.
You are probably correct about the speed he used to come up with this alter course time but obviously he did not share it with the Navigators - what an arrogant twit! It is even possible that he paid slight attention to the ice reports and thought the late turn would take him south of the pack ice. One would have thought that Boxhall and co. would highlight this in their evidence to support Smith, but they didn't so they didn't know about it.
One would think that if lowly Captain James Moore of Mount Temple had the savvy to disregard company direction and continue further south past The Corner to avoid the ice - the mighty Captain Smith would have done even better.
This time thing and Boxhall's CQD still intrigues me.
David; think about this:
A vessel travelling on a course of 266T will increase her westerly longitude as follows:
@ 21.0 knots.....28 minutes/hour.
@ 21.5 knots.....28.4 minutes/hour.
@ 22.0 knots.....29.5 minutes/hour.
@ 22.5 knots.....30. minutes/hour.
At an average speed of 22.3 knots it is 29.95.
If for instance, Titanic turned at 1750 hours when she was at say; 47 degrees,04minutes west.
and Boxhall reckoned she was at 50 degrees,14 minutes west at time of impact - this would mean she increased her westerly longitude by a total of 3 degrees, 10 minutes in the time it took.
That's 190 minutes of longitude. Divide this by the relative hourly rate of change as shown above (Boxhall used 22.0 knots) and you get this:
190/hrly.change @ 22.0 knots = 6Hr.26min.
In other words; Boxhall reckoned Titanic had travelled a total of 141.7 miles since she turned.
Now: If we add 6hrs 20 minutes to the time of turn i.e.5:50pm we get a time of impact-12:16am on Monday morning on an unretarded ship's clock. Retarded clocks would show 11:42pm on Sunday night.
However don't get excited! Remember, the second DR CQD Longitude was based on Titanic having travelled 141.7 miles since 5:50pm. We now know she only travelled about 128 miles after she turned in the vicinity of The Corner.
I know Boxhall worked his CQD from the 7:30 sights. If the clocks had been retarded 24 minutes before impact and impact took place at 12:16 then Titanic had steamed for a total of
4 hours 46 minutes and 105 miles since time of sights. This would place her 36 miles from when she turned at 5:50 - again, a total of 141 miles.
I therefore conclude that Boxhall never made a mistake in his navigation.. he just read the wrong clock. Everything fits too well! |
Samuel Halpern
Member
Username: cmdrsam
Post Number: 2539
Registered: 3-2003
| | Posted on Sunday, May 24, 2009 - 8:31 pm: |
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Jim, what clock are you taking about? Boxhall was quite clear about the time he used when working up the CQD position. 11:46 p.m.
If you work that back to 5:50 at a speed of 22 knots along the reciprocal of 266 true, you come to an a/c point about 41-55N, 47-19W which why he said at the BI that ship ran to south and west of the corner before turning. It's the only thing he could come up with since he believed his position was accurate, which we know it was not.
You know what I believe was the cause of his position being so far west of the wreck site. The same common denominator which caused the initial CQD to also be far off to the west. It had nothing to do with planned clock changes or expected midnight positions. It's a CQD OM.
Sam Halpern
TITANICOLOGY
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Jim Currie
Member
Username: sailorjim
Post Number: 430
Registered: 4-2008
| | Posted on Monday, May 25, 2009 - 5:06 pm: |
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Afternoon Sam.
Boxhall's 11:46 time coupled with a speed of 22 knots does not make sense.
In the following, I disregard the erroneous CQD position and work things back from a known position i.e. that of the wreck or close to it.
The first calculation uses Boxhall's impact time of 11:46pm and the second, the official time of 11:40. Perhaps Boxhall used the time of the final 'stop' order ?
By my reckoning: using speed: 22.0 knots, course: 266T, DR sinking point:41:45'N - 49:57'W and lapsed time of 5hrs 55 minutes; Titanic altered course on the 14th when she was at 41:54'N. - 47:02'W. This puts her 5 miles in the direction 195T from The Corner.
All else remaining the same but changing the time of impact to 11:40pm puts Titanic at 41:54'N.,47:05'W when she made the turn. This alternative position is 7 miles in the direction 237T. from The Corner.
You remark:
"If you work that back to 5:50 at a speed of 22 knots along the reciprocal of 266 true, you come to an a/c point about 41-55N, 47-19W".
That position is 15 miles in the direction 250T from The Corner.
Since we have two 'fixes' - The Corner and Noon on the 14th as well as other evidence; we can be fairly confidant that Titanic was heading close to 240T just before she turned at 5:50. She would have been on this heading when passing the position of The Corner and would bear 240T from it [The Corner]at the point and time of turn. This suggests to me that the DR position of the turn calculated using an impact time of 11:40 is more realistic and closer to fact. If so there is a difference of 8 or 9 miles between your back-calculated DR and the one in which I used an impact time of 11:40 .
At 22 knots Titanic would have taken between 22 and 24 minutes to cover that distance.
I have no idea what clock Boxhall was using but I am fairly sure there is a constant time error running through this part of the tale.
That error relates too closely to half the planned clock change to be a coincidence.
You sum things up yourself when you remark :
"It's the only thing he [Boxhall] could come up with".
This little exercise has exposed another anomaly.
It has been agreed that the distance from Noon on the 14th to The Corner was 126 miles. If this was so and Titanic over-ran The Corner by 7 miles then she ran a total of 126+ 7 = 133 miles from Noon before she turned at 5:50. So what was her average speed from Noon on the 14th?...22.8knots?
At the UK Enquiry Boxhall remarks:
"15672. If she was going 22 knots and ran past the corner for 50 minutes that means she?
- I did not say 50 minutes.
15673. No, I know you did not?
- I do not remember what time it was but it was some considerable time; the difference I make between my time and the time that was given in the book - well there was such a big difference that I considered it worth mentioning to the senior Officer of the watch".
? What the heck was going on here?
126 miles from Noon to The Corner plus 'Some considerable time' which required special comment should surely have caused alarm bells to ring.
If Boxhall was using 22 knots from Noon then Titanic would have been at the corner at 5:44pm. Did Smith allow his ship to run on a mere 6 minutes or just a little over 2 miles? Somehow I don't think so. I prefer to think that Boxhall expected Titanic would be at The Corner closer to 5:30pm.
I am also becoming convinced that Titanic was indeed 'speeding'. I wondered why, since the engine revs. pointed to a speed a little over 21.5 knots - Boxhall was thinking closer to 22 knots. Perhaps Captain Lord of Californian unintentionally provides a possible answer here:
"Senator SMITH.
Does the log indicate the direction of the wind?
Mr. LORD.
The hour 11 to 12, was calm; no wind at all. Previous to that, in the early morning it was west-northwest and north-northwest; and after noon, until 10 o'clock, it was north".
The good captain was answering questions about weather throughout Sunday the 14th.
A vessel with such a superstructure as that of Titanic would benefit greatly from a 'tail-wind' not to mention any slight surface current that such a wind might have generated.
Normally, Titanic should have been stemming a slight northerly current east and north of The Corner but things were certainly not normal at that time. |
Samuel Halpern
Member
Username: cmdrsam
Post Number: 2540
Registered: 3-2003
| | Posted on Tuesday, May 26, 2009 - 2:09 am: |
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Hello Jim.
You said:
>>If so there is a difference of 8 or 9 miles between your back-calculated DR and the one in which I used an impact time of 11:40<<
You may want to check that distance again, I get closer to 10.5 miles which almost 29 minutes at 22 knots. The thing is you and I are using different starting points in addition to a different collision time. Boxhal did say that he thought the ship struck about 11:45, but he used 11:46 in his calculations, a 10th of an hour beyond the 11:40 time Hichens reported. Boxhall never explained exactly why 11:46 instead of 11:45 or even 11:40, but if Pitman was right about the sights being completed at 19:40, then Boxhall's 11:46 would make it exactly 4.1 hours beyond the star fix. But you know, I think the star fix was 15' too far west because of a misreading of the difference between chronometer and hack watch times by Pitman before the star sights were taken. A systematic error that would affect all sights taken. The red flag would have been a large difference between the fix and the ship's DR. In later years, Boxhall would claim a 20 mile difference. Errrrr!
Anyway, I got to go. I've been through all this before. Have fun with it.
Sam Halpern
TITANICOLOGY
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Jim Currie
Member
Username: sailorjim
Post Number: 432
Registered: 4-2008
| | Posted on Tuesday, May 26, 2009 - 12:50 pm: |
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Morning Sam,
Of course there's going to be a difference in the outcome of our calculations because they are dead reckonings using different arguments.
I've heard you on this 'hack watch' thing before.
I never ever heard that term used in the UK MN. Perhaps it's a US military term?
As far as I can determine the Hack Watch was developed around 1800 with the medical profession in mind. It was superseded by the Chronograph( stop-watch) before the end of that century.
The normal practice on a UK merchant vessel including passenger ships was for a junior to stand over the chronometer during the taking of sights and to note the time when the senior officer actually taking the sight to shout either 'time' or 'mark'.
In many cases, a specially ruled note book called a 'Sight Book' was used to record all sight work information when the sight or sights were completed. Either that or the junior would hand a note to the senior officer which showed the name or number, altitude, chronometer time and chronometer error of each actual sight.
All Apprentices, Cadets and Mid-shipmen had four years extensive and monotonous training at this particular part of navigation 'sports'.
I would have thought a competent navigator with an Extra Master's certificate would be able to pre-set his sextant to the approximate altitudes and would know azimuths of any heavenly bodies he intended using in a multiple sight. In that way he would not take ten minutes to actually take all his sights - more like two minutes - even reading a verier sextant. I know this myself, having used one for many years. The vernier scale was engraved silver and was read using a small magnifying eye-piece mounted on a swivel attached to the main arc support.
These were very experienced navigators who could read the night sky as easy as we read a newspaper. They knew all the principal stars and planets that would be visible during their particular times on watch. They would automatically make allowances for the slow change of heavenly bodies relative to the horizon and meridian. They knew that stars rose, culminated and set 4 minutes earlier each night.
Most senior men had this down to a fine art. To have taken ten minutes to perform such a task in the most perfect of conditions is highly unlikely. I would have had serious staff replacement thoughts myself.
Pitman probably meant that all preparations for commencing the actual working of the sights were completed by 7:40hrs.
A stop watch is not a good idea taking sights - too many opportunities for error. I suppose that's why we never used them. Better to go directly to the 'horses mouth' so to speak - the chronometer.
As a foot-note: navigating in the N. Atlantic where the opportunity to get any kind of celestial observation is a usually a brief shot between clouds from a rolling deck -is an art in itself. Navigators learn to make very quick observations. Navigators on quick ships also know to make quick multiple observations. |
Samuel Halpern
Member
Username: cmdrsam
Post Number: 2541
Registered: 3-2003
| | Posted on Tuesday, May 26, 2009 - 6:12 pm: |
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Good afternoon Jim,
If you have a chance to find or have a copy of: 'The Practice of Navigation and Nautical Astronomy' by Henry Raper, Lieut. RN, FRAS,FRGS, 19th Ed., Revised and enlarged by Cmdr Thomas A. Hull, RN., [Pub. by J.D.Potter (sole agent for the sale the Admiralty Charts) Poultry & 11 King St., Tower Hill, 1891.], go to Ch III, 'Taking Observations'. There is a section (III) in that chapter called 'Employment of the Hack Watch', pp. 202-203. The hack watch was a portable chronometer or good watch used during the taking of observations, and was supposed to be compared to the standard chronometer before and after observations were taken. They detail the procedure that was supposed to be used so that the time of the observations were correctly adjustment for all errors. On Titanic, the standard chronometers were kept in the chart room behind the wheelhouse. Not exactly close to where the observations would have been taken out on the bridge wings. It was Pitman who said the taking of the sights were completed about 20 minutes to 8. He would have been the one taking down the times while Lightoller took the sights, and recorded all the results.
Sam Halpern
TITANICOLOGY
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Jim Currie
Member
Username: sailorjim
Post Number: 433
Registered: 4-2008
| | Posted on Tuesday, May 26, 2009 - 9:31 pm: |
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Evening Sam,
I don't have the luxury of access to old RN publications where I live but since the edition you refer to is the 19th one, I can only assume that a great deal of what was in the original one was retained. The original 'hack watch' supplied to the Navy was really the fore runner of the stop watch. Not a portable chronometer.
A mechanism inserted a wire into the gearing to temporarily stop the clock as it were. (very crudely described I must add).
These were manufactured up until 1820 I understand. Perhaps the name 'Hack' was retained to describe watches which could be stopped and started at will.
I do know that Dent and Company of London supplied such watches to the RN for their old warships but the oldest of these was de-comissioned after WW1.
As I stated before, this is obviously a military term and was still in use with the armies, air forces and navies well after WW2. Hence the reason I have never heard of it used on an MN ship. Nor have I seen a stop watch used on such ships.
I would be interested to see how a 'Hack' watch would work with multiple sights. I would imagine that when the sight-taker shouted 'time' the watch would be started and the the person with the watch would walk to the chronometer and when he was ready - stop the watch and note chronometer time at that moment. he would then subtract watch time from chronometer time to get the exact time of the sight. That's fine for one sight although a bit clumsy to say the least and very vulnerable to error. Perhaps that's why the RN anchor badge shows a fouled anchor and the MN never adopted the practice?
In every ship I served on, the chronometer was usually kept in gimballed, rose-wood box, the inside of which was lined with dark blue velvet. The box was normally kept in top-opening cabinet which would be incorporated into the end of the chart table. The inside-top of this cabinet was of glass and the wooden covering lid fitted flush with the chart table.
When it was time for sights the wooden lid would be raised and hinged back.
When it was time time to wind the chronometer(s) both lids would be raised.
From what you tell me about Titanic - she had much the same arrangement.
We always had a man at the chronometer with the sight book and the sight-taker on the bridge.
It's very quiet on the bridge of a ship. The shouted word 'time' can very easily be heard behind the curtain of the wheelhouse door even from the bridge wing of a VLCC almost twice the size of Titanic - believe me! |
Samuel Halpern
Member
Username: cmdrsam
Post Number: 2542
Registered: 3-2003
| | Posted on Wednesday, May 27, 2009 - 1:58 am: |
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The reference described the hack watch as a portable chronometer or good watch used during the taking of observations. Nothing like what you describe.
Sam Halpern
TITANICOLOGY
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Dave Gittins
Member
Username: gittins
Post Number: 4055
Registered: 4-2001
| | Posted on Wednesday, May 27, 2009 - 10:41 am: |
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After Sam raised the idea of a one minute error caused by the use of a hack watch, I ran the idea past a modern master.
He told me that in his youth the possibility of just such an error was known. To prevent it, his line made sure that the chronometers were always within earshot of the bridge, so the times could be taken as Captain Jim describes. So Sam's idea is possible, but perhaps unlikely.
Dave Gittins
Titanic: Monument and Warning.
http://users.senet.com.au/~gittins/Book.html
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Charles B. Weeks Jr.
Member
Username: charles_weeks
Post Number: 254
Registered: 8-2002
| | Posted on Wednesday, May 27, 2009 - 9:42 pm: |
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Sam,Dave & Jim:
Once in my career, I saw a Hack Watch used, it was on the training ship. You can imagine 30 cadets trying to get into the chart room at once. Otherwise we always used a stop watch to measure the time from when the sight was taken until the chronometer was read. Our chronometers were as Jim describes them, except the velvet was green not blue.
Regards, Charlie Weeks |
Dave Gittins
Member
Username: gittins
Post Number: 4057
Registered: 4-2001
| | Posted on Wednesday, May 27, 2009 - 10:12 pm: |
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So timing sights in the way Captain Weeks described could produce a one minute error if the chronometer was not read correctly, but it would only affect that particular sight. It wouldn't give an error of 15 minutes in a whole set of sights. When the sights were reduced, the error would be obvious.
Dave Gittins
Titanic: Monument and Warning.
http://users.senet.com.au/~gittins/Book.html
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Samuel Halpern
Member
Username: cmdrsam
Post Number: 2544
Registered: 3-2003
| | Posted on Thursday, May 28, 2009 - 3:51 pm: |
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Gentlemen:
I'll be happy to privately email you the described procedure for taking the time of sights using a portable chronometer or hack watch as it was also called. It's all in two pages.
The proper correction procedure described involves a before and after comparison to the standard chronometer. If only one of the two comparisons were taken, and that correction used, it is very possible for a 1 minute systematic error to come into play. That 1 minute error in time would affect all the sights taken, not just one, by 15 minutes of arc. The lines of position of all sights would be equally affected and shifted the same way. They would all cross close to each other and look like perfectly good fix. Comparing the fix to the DR should give the navigator a clue that something is very wrong because an unusually large gap between fix and DR would show up. Then they would have decide which was in error, the fix or the DR.
Pitman said they finished with the sights about 19:40 and he started to work them up in the chart room when Boxhall arrived at 20:00. How far along did he get before handing them to Boxhall is not said. But it seems if a misreading of the chronometer had taken place, it most likely would have been Pitman who did that. Boxhall may have simply taken the correction given to him and used it in his subsequent work. As you all know, there are many correction errors that must be taken into account. Some that are sight specific such as refraction errors, others like height of eye and index error, that affect all sights taken.
By the way, seaman Albert Horswell referred to one of the portable chronometers before the Wreck Commission.
12429. Did you go straight to No. 1 boat then? - No. I was ordered to the port emergency boat. I was ordered to put the lantern in the boat and a chronometer. I did that and came out again, and I was sent to the starboard boats. Then I was ordered into No. 1 boat.
Sam Halpern
TITANICOLOGY
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Jim Currie
Member
Username: sailorjim
Post Number: 434
Registered: 4-2008
| | Posted on Thursday, May 28, 2009 - 4:30 pm: |
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Good Afternoon Lads (I use the term advisedly)
I have been wracking what brains I have left to try and find out where I heard or read about the 'hack' mechanism I described to Sam.
I think is was in the journal of the British Horlogical Institute. It described a watch which had a wire with a hooked end which temporarily interrupted the escapement movement. They were in vogue between 1800 and around 1820 when the new portable chronograph watch replaced them. I understand they were still described by some as a 'hack watch'. These chronographs were used by the RN right up to 1907 when several commanders complained to the Admiralty about errors in the minute and second hand readings. The then chronographs were corrected and modified and renamed as 'hack watches'. They were little better than an accurate stop watch. The last of them went to the scrap yard with the old ships which had them shortly after WW1.
The more modern chronograph was set to the chronometer and checked against it before use for celestial observations. At other times it was used for manoeuvring, timed execution of orders and synchronisation between ships at sea.
Merchant ships had little or no need for such sophisticated instruments. Their conning and command position plus chart room and steering position were all located within the same area.
You will note that 5th Officer Lowe of Titanic had a watch but it was set to GMT as would be the Chronometer. I suspect that all his and the other navigating officers worked in GMT and converted their results to ship's time as and when necessary. If you're looking for a timing error; try that for size!
Reading their accounts; it seems they seldom marked DR positions on the chart except when coasting. (navigating in sight of land).
In addition; although they did have traverse tables, I suspect they were purists and used 'The Sailings' as opposed to the quick Traverse Table methods. Actually I preferred that way myself - helped to pass the time when way out at sea. (Apprentices were very useful then!).
Using GMT as standard time had its advantages as well. There was no need to play with time until some result or other had to be noted in the logbook.
As for using a 'hack' or 'stop' watch - what would be the advantage if it had to be re-set each time? If Lowe was using his watch set to GMT during the taking of the six or seven observations around 7:30hrs on the evening of the 14th - he would merely have read his watch and noted the GMT of each sight - like having a wrist chronometer. If he had set his watch a minute fast or slow of the ship's chronometer then he would have had the same error with every observation.
For Latitude, he worked about three stars near or on the meridian. Since the latitude was not differing very much, an error in time would not be significant.
I've been thinking about the effect of using a wrong clock reading in the case of star sights.
My memory of this is very dim - it's over 30 years since I had a sextant. You'll forgive me all you nav. experts and math geniuses if I don't get it quite right.
The observed Longitude found by star sight is the difference between the Local Hour Angle (LHA) of the star and it's Greenwich Hour Angle. To find the latter you need to have the GHA of Aries and the Sidereal Hour Angle (SHA)of the particular star at the moment of taking the sight. These are obtained from the Nautical Almanac, using the exact GMT of taking the sight.
You will note that the GHA (Greenwich Hour Angle) of the first point of Aries changes about 15 degrees of arc every hour equal to 4 minutes of arc every minute of time.
Therefore a 1 minute error of time would produce a resulting error of 4 minutes in the GHA of the star and consequently in the calculated longitude. If I'm right then to have a 16 minute error in Longitude; there had to be an error of close to 4 minutes between the ship's chronometer and the clock used to record time of sights. That is not the kind of error easily missed by a professional navigator. |
Samuel Halpern
Member
Username: cmdrsam
Post Number: 2545
Registered: 3-2003
| | Posted on Thursday, May 28, 2009 - 5:27 pm: |
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>>You will note that the GHA (Greenwich Hour Angle) of the first point of Aries changes about 15 degrees of arc every hour equal to 4 minutes of arc every minute of time.<<
15 degrees per hour divided by 60 minutes per hour of time is 1/4 degree per minute of time. A 1/4 degree is 15 minutes of arc (15'). Therefore, a 1 minute time error produces an error of 15', not 4'.
>>You'll forgive me all you nav. experts and math geniuses if I don't get it quite right. <<
Forgiven!
Sam Halpern
TITANICOLOGY
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Arun Vajpey
Member
Username: zekenwolf
Post Number: 200
Registered: 4-2009
| | Posted on Thursday, May 28, 2009 - 6:04 pm: |
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This is getting to be quite a Hol(e)y War! |
Jim Currie
Member
Username: sailorjim
Post Number: 435
Registered: 4-2008
| | Posted on Thursday, May 28, 2009 - 6:53 pm: |
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I just knew you'd spot that one Sam! - All 60's 4's and 15's! Why do you think I wrote the following:
>>You'll forgive me all you nav. experts and math geniuses if I don't get it quite right. <<
Hell! you can't win 'em all.
So now you've 'marked my paper' - what about the rest of it? Was it Boxhall or Lowe who remarked that they thought the ship was way ahead of where she should have been? Obviously Lightholler thought he would be up with the ice around 9-30pm while Moody, on the same watch thought it would be much later. Both Lowe and Pitman thought Titanic had turned late in terms of time. Obviously there was a problem of time running throughout the period. Perhaps the chronometer had developed an error? It would have been spot-on 4 days earlier but they did not have a means of checking it at sea at that time. Even then; a cumulative error of over 1 minute in less than a week was most unusual - even in those days. |
Samuel Halpern
Member
Username: cmdrsam
Post Number: 2546
Registered: 3-2003
| | Posted on Thursday, May 28, 2009 - 11:26 pm: |
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I believe the Titanic was equipped with two chronometers. Now where did I read that?
I agree that it would highly unlikely for that much of an error to accumulate over that short a period. The delayed turn of the corner first came up at the British inquiry. There Pitman said he thought the ship should have turned the corner about 5 p.m. But a few weeks earlier, he said the ship turned the corner at 5:50. Neither he nor Boxhall said anything about a delayed turn in America. I think they both were searching for some logical explanation of how the ship could get as far west from the corner as Boxhall's CQD if the turn was made at the corner 5 hours 50 minutes earlier. They of course couldn't cover the 145 miles from the corner to Boxhall's position in that amount of time at only 22 knots.
Sam Halpern
TITANICOLOGY
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Charles B. Weeks Jr.
Member
Username: charles_weeks
Post Number: 255
Registered: 8-2002
| | Posted on Friday, May 29, 2009 - 1:25 am: |
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Jim:
If my faded memory serves my right, it was Boxhall who commented on being ahead of their DR, in his 1962 radio talk on the BBC. Somewhere in the world of ET is a transcript of that show that Cathy Akers-Jordan and I produced, and it is in it.
I believe this topic began with us looking for an answer to why Boxhall's CQD position is approximately 13 miles west of the wreck. Sam and David Brown and I have discussed this topic many times, and Sam has done further research on the subject. This lead Sam to write his article "A Minute in Time". The minute in time is just one of the possible answers to the question about Boxhall's CQD position. I find it interesting that in testimony, Boxhall couldn't remember the Lat. & Long. of the star fix, but he told how he advanced it along the track line to 2340 to get the CQD position, and no one asked him to do it for the hearing. I have worked it backward from the CQD to the star fix and I know Sam has too. I just can't find my plotting sheet at this moment.
Which brings up another point, as I read the testimony of Titanic's officers I understand them to say that they did a lot of DR calculations in their heads, where as we would step it off on the chart. I don't know about your mental arithmetic but with me its better stepped off on the chart.
Regards, Charlie Weeks |
Dave Gittins
Member
Username: gittins
Post Number: 4060
Registered: 4-2001
| | Posted on Friday, May 29, 2009 - 9:51 am: |
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"I believe the Titanic was equipped with two chronometers. Now where did I read that?"
Maybe in my e-book. It comes from the Report of Survey of an Emigrant Ship, completed before the voyage.
I think that as Titanic approached the 'corner' Boxhall and Pitman were simply 'out of the loop'. Wilde was navigating and there's a report of him conferring with Smith. A little reflection would have told Boxhall and Pitman that the ship couldn't possible reach the 'corner' by 5-00pm. That required 25 knots or so.
By the way, the Board of Trade methods of the time were intended to minimise plotting on the chart. Navigators used methods that gave Lat and Long in figures. Important positions, such as the noon position, were marked on the chart, but the actual working was strictly arithmetic. Sumner's position lines were known and were required by the extra master's certificate, but purists didn't approve, because they involved plotting.
Dave Gittins
Titanic: Monument and Warning.
http://users.senet.com.au/~gittins/Book.html
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David G. Brown
Member
Username: brown
Post Number: 2276
Registered: 12-2000
| | Posted on Friday, May 29, 2009 - 12:54 pm: |
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Discussion about chronometers and hack watches is interesting, but pointless with regard to the so-called 7:30 p.m. star sights. The reason is that absolutely not historic record exists of the lat/lon coordinates created from these sights. In fact, there is no contemporaneous record that the resolving of the sights was ever completed. Thus, any attempt to re-create the fix obtained (or not obtained) from these sights is simply making guesses about assumptions and is thus twice removed from historic reality.
What is obvious by inspection of the available hard data is that the first set of CQD coordinates sent by Titanic were for the ship's predicted midnight location. To navigators, "midnight" always refers to the start of the new day and never to the end of the old. Therefore, the first coordinates predicted the ship's position at 0000 hrs April 15th. That converts to 2447 hrs in April 14th time.
The second set of coordinates which Boxhall admitted to working out are 20 minutes of steaming at 22 knots retrograde from the first set. That is, they are for midnight minus 20 minutes. In everyday street language, that would be "11:40," which is the most-often quoted time for the accident.
(The 22 knot speed is based on Boxhall's testimony that he used it for his calculations.)
Actually, because it was back-computed from midnight, the time of the accident must rightly be stated as "minus 11:40." This gets confusing because a minus o'clock time is neither a.m. nor p.m. So, sticking to the 24 hour system of time reckoning makes more sense.
It is a given that midnight is 0000 hrs of the new day. This means that all of those 47 extra minutes needed to keep Titanic's clocks in sync with the sun were added to the end of April 14th date. So, 2400 hrs was not the end of April 14th. It would have continued until 2447 hours, or midnight when April 15th was to have begun.
0000 hrs Apr 15/2447 hrs Apr 14 = midnight.
-20 minutes = -2340 hrs Apr 15 or 2427 Apr 14
We know for a fact that the accident did not take place at 2447 hrs using April 14th time. Quartermaster Hichens stated he was on duty until 2423 hrs April 14 and that the accident occurred before he was relieved.
From numerous crewmembers we know that the accident took place just before the wakeup bell rousing out the watch below. This puts it at about 11:40 p.m. prior to midnight. But, that time cannot be in April 14th hours. If it were, then the crew change of watch would have come at 2400 April 14th and the oncoming Port Watch would have served all 47 extra minutes. There was no doubt among surviving crewmembers that those extra minutes were to be split between the two crew Watches. To do so meant that the change of watch had to have been scheduled for 2423 hrs April 14th, just as Hichens testified.
So, if the accident took place 20 minutes before the crew's "midnight" change of watch, then the on-duty Starboard Watch must have already worked off its 23 extra minutes. This would have required retarding the crew clocks by 23 minutes sometime during the 8-to-12 watch. To get the time of the accident in April 14th hours it is therefore necessary to add back the 23 minutes, yielding a 2403 hrs April 14th for the time of the accident.
Note that Boxhall's coordinates were for 2427 hrs in April 14th time. Because they were back-computed from midnight (2447 hrs), they included 24 extra minutes never served by the off-duty Starboard Watch. Subtracting those never-served minutes yields a now familiar time:
2427 – 24 unserved minutes = 2403 hrs April 14th.
The obvious conclusion is that both sets of Titanic's CQD coordinates were off for the same reason – improper use of "midnight." The first set was based upon the true midnight marking the predicted position where Titanic would have started April 15th date and time. The second (Boxhall) position is for 20 minutes earlier, but still based on April 15th midnight.
-- David G. Brown |
Jim Currie
Member
Username: sailorjim
Post Number: 436
Registered: 4-2008
| | Posted on Friday, May 29, 2009 - 1:09 pm: |
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I'm really enjoying this now guys!
I've been playing around with figures (stand-by in case I need you Sam!).
To determine the effect of chronometer error on latitude sights, I carried out an exercise involving a star near the meridian (Canopus(17) Az.about S6E).
Anyway, to cut a long story short - I found that a one minute error on the chronometer resulted in an increase of 1.9 minutes in the intercept away from the DR position, placing the vessel north of her true position. There would also be a distortion of the position line(s) due to change in azimuth resulting in a very distorted 'fix' from multiple sights.
I cannot believe that Pitman did not use Polaris on such an east west course. The result of that sight in itself should have caused him to question the latitude results of his other sights.
Hi Charlie!
I read somewhere that Smith actually plotted the 1930 hrs sights and that he 'pricked' them off on his chart. I also read that the Navigators did all their work in nav. work books. These were the fore- runner of of our Sight Books - you may remember you could by a proper ruled -out hard batter version from any good nautical Publisher.(Brown Son & Fergusson).
Dave,
I think Sumner's Position Line method was superceded by the Marc St Hilair method later in the 19th. Century. As you know it involved calculating the Azimuth.
I think you'll find the officers of Titanic used that method. They might also have used a plotting system called the 'Aquino's Protractor Diagram' I think I have a copy somewhere I can let you have if you don't already have one. What is almost Certain is that those of them who were trained after 1903 would have used Nicholls's Concise Guide Volumes 1 and 2. They taught, among many other methods of navigation; the Marc St Hilair intercept method. These guys were highly skilled in the art of navigation mathematics. As I've said before in these pages; 'they ate, slept. drank, talked and dreamt the subject. The competition between them would have been immense. To make such a fundamental error of reading a chronometer wrongly would be Like forgetting the wife's birthday! |
Jim Currie
Member
Username: sailorjim
Post Number: 437
Registered: 4-2008
| | Posted on Friday, May 29, 2009 - 1:34 pm: |
|
David,
You write:
"In fact, there is no contemporaneous record that the resolving of the sights was ever completed."
I' sure you well know the meaning of the word 'contemporaneous' so what on earth was Boxhall waffeling-on about when he gave the following answers to questions put to him at the enquiry?
15626. As to the stellar observations that were worked up for the 7.30 position, did you work them up?
- Yes.
15627. Did you get them from Mr. Lightoller?
- Mr. Lightoller took the observations at half-past 7, before I went on deck.
15628. That is what he told us; he took the observations and gave them to you, and you worked them out?
- Yes.
15629. And the Captain put the position at 7.30 on the chart at about 10?
- Yes.
I presume Boxhall was talking about stellar observations taken during the evening of 14th.April,1912? |
Samuel Halpern
Member
Username: cmdrsam
Post Number: 2547
Registered: 3-2003
| | Posted on Friday, May 29, 2009 - 7:06 pm: |
|
The Marcq St. Hilaire method was first published in 1875. I understand it was introduced in RN in 1886, and into the MN about 1908. But that doesn't mean it was widely practiced at that time.
Sam Halpern
TITANICOLOGY
|
Charles B. Weeks Jr.
Member
Username: charles_weeks
Post Number: 256
Registered: 8-2002
| | Posted on Friday, May 29, 2009 - 10:29 pm: |
|
Jim:
I agree that Capt. Smith probably did plot the star fix on his chart, and very possibly Boxhall plotted it on the officer's chart. However I don't believe Lightoller, saw this, it would have ruined his night vision. Murdoch should have seen it when he relieved the watch. Also Lightoller did mental calculations to get a time when he should be up to the ice. I would have stepped it off on the chart. The fact that he and Pitman came up with different answers is I believe due to they're working from different radio messages.
Shooting six stars is fine, but three for Lat. and three for Long. seems a bit much. I'd try to space them around the compass about 60 degrees apart in Azimuth, and yes Polaris definitely would have been one. I'd be looking for a pinwheel when they were plotted.
Yes I still have my Nav. Notebook where I worked out my sights and the resulting fix.
Regards, Charlie Weeks |
Dave Gittins
Member
Username: gittins
Post Number: 4061
Registered: 4-2001
| | Posted on Saturday, May 30, 2009 - 10:11 am: |
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I don't have the book about the extra master's exam on hand, but I'm pretty sure it didn't include Marcq St. Hilaire. It certainly included Sumner lines. Quite a few things were around that were not part of the official methods. There were even some slide rules, but I don't know if they were used for celestial navigation.
The Board of Trade exams were slow to change. Until 1906 the extra master had to be able to find longitude by the lunar distance method! The six star fix was about par for the course.
The Board of Trade method didn't give the pinwheel described by Captain Weeks. It gave latitude and longitude in figures, without plotting. Stars bearing about north or south gave latitude, using a method called latitude by reduction to the meridian. (Not the same as the more recent ex-meridian tables). Longitude needed stars bearing roughly east or west. The could be quite a considerable way from a westerly or easterly azimuth. In the example in my e-book, the longitude was obtained from a sun sight at around 3-00pm ATS.
The Board of Trade methods were all based on spherical trigonometry. Even a Polaris sight was far more complex than it later became.
To add to the fun, in 1912 the tables gave trigonometrical functions for hours, minutes and seconds, instead of degrees. The last step in the longitude sight was to convert the longitude from time into degrees.
As Captain Jim says, the officers of 1912 were very much into navigation and were very good at it, which makes Boxhall's little lapse very mystifying. One of my suggestions is that he used a log of a sine instead of a log of a cosine at a critical point.
Dave Gittins
Titanic: Monument and Warning.
http://users.senet.com.au/~gittins/Book.html
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Jim Currie
Member
Username: sailorjim
Post Number: 438
Registered: 4-2008
| | Posted on Saturday, May 30, 2009 - 3:19 pm: |
|
The reason I believe they used Marc St Hilair was that the BoT recommended the use of both volumes of Nicholls's guides for MN training establishments very soon after it was published in 1903. My very first copy of Volume 1 (for Apprentices and 2nd Mate's Certificate) was published before 1921. It was given to me by it's first owner who retired around 1950.
Don't know about slide rules in 1912 but I do know they were banned from exam rooms in the early 50s.
I agree with Charlie about the number of stars 'shot' that night. Personally I would have been more concerned about westerly progress-
especially when on a course a few degrees south of due west and in a ship travelling at around 22 knots toward a north-south trending ice barrier. I would most certainly have known the rate at which my westerly longitude was increasing as would have done Lightholler and any other navigator worth his salt.
I also think you're right,Charlie about Lightholler and Moody - they were not 'singing from the same hymn sheet' Either they were using different 'targets' (reported positions of ice)or were working from different starting points.
Lightholler was using an easterly boundary (target) of 49W for the ice and thought he would be up with is around 9:30pm
Moody calculate they would be at the ice around 11:00pm.
If Lightholler reckoned they would be up at the ice by 9:30pm that had to be 3hrs 40 minutes after turning onto the 266T course.(he made his calculation after 6:pm). Working back from 49W points to Titanic having turned when she was somewhere between 12 to 15 minutes of longitude west of The Corner - 11 or so miles past it. I think it was Pitman who thought they were 10 miles past it when they turned!
Let's look at Mr. Moody's work.
He reckoned the ship would be up with the ice at 11:00PM. what were his references?
Let's assume he started from approximately the same base as Lighholler. However his 'target'was 1 hour 30 minutes in time further west. Converted this time to degrees of Longitude, it would be about 43 minutes further west...i.e. at 49 degrees,43 minutes west.
40 Minutes later, Titanic would have been at about 50 degrees west - not much further west than where the wreck is now!
It would seem therefore that you are right Charlie and they were not using the same 'targets' or ice reports.
(By the way David; this is all in real time and I suggest, helps to confirm the actual steaming time from turn to impact - no room here for an extra 23 or 4 minutes).
Dave, you wrote:
"I don't have the book about the extra master's exam on hand, but I'm pretty sure it didn't include Marcq St. Hilaire."
Actually it wouldn't. The exams for Master and Extra Master did not include much practical navigation which included the various position line methods - that was all done in the 2nd Mate and 1st.mate exams. The higher exams dealt more with theory and construction as well as- in the case of Extra Master -in depth examination of the mathematics involved in navigation.
Extra Master in my day was split into part A and B.
Sam,
The RN used the Admiralty Manual of Navigation.
There are quite a few examples of MN navigators having their 'feathers ruffled' by ex RN navigators over the comparisons made between the two. There was always a great though friendly rivalry between the two services. The MN reckoned the RN were amateurs who only went to sea occasionally or during hostilities! |
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