Keeping Track of a Maiden Voyage

[Tad G. Fitch]

Good point. As Sam has demonstrated, the methodology he used matches the distances in the Olympic log, and that speaks volumes, especially when the other method does not work out this way.

 

[L. Marmaduke Collins]

Samuel Halpernosted Posted on Thursday, May 24, 2007 - 1:33 am:

Distance from Daunt's Rock to corner = 1504+173.6 = 1677.6 miles.

Samuel Halpern: Posted on Sunday, May 27, 2007 - 11:02 pm:

...if you take the data reported on Olympic's log for the distances the ship ran for the first three days and then add the distance from the third day's noon location to the corner you get the total that I gave above. ...
For the Titanic I got a distance to the corner of 1675, a number consistent with those distances to the corner for the Olympic taken from three separate voyages

Why do you insist on posting erroneous information? Not until I sent you a private email explaining your error did you acknowledge it in your post of:

Samuel Halpern: Posted on Thursday, May 31, 2007 - 2:32 am:

Finally, the rhumb line distance from the noon position for June 18 to the corner is 173.6 nm. Total distance adds up to 1680.4 nm.

What I did is add up the distances reported in the log for the first three days to the noon position for June 18, which was 428+534+542=1504. I then added to that the 173.6 nm from noon to the corner to get 1504 + 173.6 = 1677.6 nm. The difference between the two methods is 2.8 nm.

I am amused by your armchair cohorts trying to support you. If Olympic or any ship runs 1680.4 nautical miles, and it is shown as 1677.6 miles that is incorrect. Also, if the course from off Kinsale is 256 degrees true, that is an error that puts the ship on a grounding course on Fastnet. When a distance is 131 nautical miles, fudging it to be 126 is incorrect.

 

[Tad G. Fitch]

And frankly I am amused by your failure to explain how the methodology Sam used matches the distances recorded in Olympic's log, while the methodology you claim the crew would be using doesn't match what they recorded in the ship's log. The debate is not which method is more accurate, but which was actually used.

 

[Samuel Halpern]

Dear Capt, Collins. With all due respect, I did NOT acknowledge an error in my post of May 31. To remind you, in your post of May 30, 2007 - 2:43 pm you wrote:

Sam, as a marine navigator you disappoint me. Believe me taking the data reported on Olympic's log for the distances the ship ran for the first three days and then add the distance from the third day's noon location to the corner you get the total = 1680.4 nautical miles.

In my post of May 31, 2007 - 2:32 am I was kind enough for the benefit of the readers (who I'm sure are quite amused by all of this by now) to explain to them how YOU were able to derived a distance of 1680.4 nautical miles.


To repeat what I wrote (this time with little emphasis in bold face):

What Capt. Collins did, using meridian parts calculations throughout, was to start from Daunt's Rock LV and go to a point south of the Old Head of Kinsale and then to a point 3 miles south of Fastnet Light. That gave him a distance of 56.1 nm. From there he took a rhumb line course (constant course angle) to the reported noon position for June 16, which by meridian parts calculation, is 372.3 nm. The total distance for the first day was given by adding these two distances together which gave 428.4 nm, which is close to the 428 nm written in the log card. The distance for the second day was given by taking a rhumb line from the noon position for June 16 to the noon position for June 17. That gave 535.7 nm by meridian parts calculation, compared to 534 nm that was written in the log. The next distance was given by taking a rhumb line from the noon position for June 17 to the noon position for June 18. This gave 542.7 nm by meridian parts calculation, compared to 542 nm written in the log. Finally, the rhumb line distance from the noon position for June 18 to the corner is 173.6 nm. Total distance adds up to 1680.4 nm.

The method I used to get the distance from Daunt's Rock to the corner made use of the run data from the log card itself. As I explained, I simply added up the distances reported in the log for the first three days to the noon position for June 18 (the 3rd day out), which was 428+534+542=1504. I then added to that the remaining 173.6 nm from noon to the corner to get 1504 + 173.6 = 1677.6 nm. It can't get much easier than that.

Your problem I'm afraid is not with me or the method I used. It is with the distance data in the abstract logs taken for Olympic's three westbound voyages in 1911 while she was on the southern route. Using the very simple method of adding the remaining distance from noon to the corner to the sum of the distances reported in the log for the first three days out, we get total distances to the corner from Daunt's Rock of 1677.6, 1674.6, and 1676.2 for those three westbound voyages. And in my work on estimating Titanic's positions, I got a calculated distance to the corner of 1675.5 nm (or 1675 if you add just the rounded numbers up) which matches well with the above.

So why don't you just come out and say it. Those officers who worked out the distances on those Olympic crossings were not very good marine navigators because they posted numbers that don't agree with your much more precise method?

 

[L. Marmaduke Collins]

Your problem I'm afraid is not with me or the method I used. It is with the distance data in the abstract logs taken for Olympic's three westbound voyages in 1911 while she was on the southern route.

Sam: I agree with you entirely. Although, we do not always agree, I do have the utmost respect for you and your ET posting.

The method I used to get the distance from Daunt's Rock to the corner made use of the run data from the log card itself.... It can't get much easier than that.

That is, also, a fault of too many deck officers, " the easy way"


Reference, Olympics Maiden Voyage Log Card and WT message : On Board Olympic, via Cape Race, 9:30 A. M., June 19, 1911,}

There are too many discrepancies between the two versions which, from a professional perspective, suggest these documents are not authentic.

Example Log Card :

4th day (June 19th): day’s run 525? Mid lat distance is 501.16 nm.

On Board Olympic, via Cape Race, 9:30 A. M., June 19, 1911
Up to this hour the Olympic has exceeded the speed promised by her builders, her average from noon Saturday to noon Sunday being 21.89 knots. Since passing Daunt’s Rock at 4:22 P. M. Thursday she has done the following: To noon Friday, 458 [sic] knots; to noon Saturday, 524 knots; to noon Sunday 542 knots. Weather fine. Present weather outlook less favorable. At this writing all going smoothly.

 

[Samuel Halpern]

Captain, this time I'm afraid, as a marine navigator, you have disappointed me.

Example Log Card:
4th day (June 19th): day’s run 525? Mid lat distance is 501.16 nm.

What you failed to take into account Capt. Collins is the route the ship was following. Before 8 pm on June 18 they were following the great circle track toward the corner. A little before 8 pm they would have altered course to follow a rhumb line toward Nantucket LV. If you add the two separate distances you will see that they should get a noon-to-corner-to-noon distance that is close to the number entered on the log. I'm afraid you made a very basic mistake here by taking a direct rhumb line between those two noon positions.

A far as the distances reported in the wireless message sent out that Monday morning, there were errors in the middle digit for the noon Friday distance (message had 458 which should have been 428) and in the middle digit for noon Saturday distance (message had 524 which should have been 534). The speed reported in the message for noon Sunday appears correct. The point here is that you cannot trust data in wireless messages all time since they are subject to transmission or reception errors or in the transcription process. If you add up the numbers on the log card, the total comes out right.

Cheers.

 

[L. Marmaduke Collins]

Captain, this time I'm afraid, as a marine navigator, you have disappointed me...I'm afraid you made a very basic mistake here by taking a direct rhumb line between those two noon positions.

Thanks! Sam . I make no excuse. I should have known better.

 

[Samuel Halpern]

No problem. It happens to all of us.

 

[Michael Kestner]

The Olympic did not follow a single rhumb line course from one noon position to the next while on the great circle track to the corner. From detailed data that I looked at from several 1931 Olympic crossings, the logbook shows that they changed true course headings mostly about every 6 hours. (Sometimes as little as 5 hours or as much as 7 hours, but most changes appeared to be about every 6 hours or thereabouts.) This means they were changing course about every 3 degrees in longitude more or less. The distances between two noon positions along the GC track would therefore be less than the single rhumb line distance between the two noon positions because they tried to follow the great circle track fairly closely, more so than what I expected they would do. I believe this is why the distances recorded on those three log cards consistently resulted in a somewhat shorter distance to the corner than what those straight rhumb line distances would give.

Many apologies for resurrecting such an old thread, but I was very interested to read this. Where can I find this information on Olympic's crossings? Is it available online, or in a book?

 

[Samuel Halpern]

Where can I find this information on Olympic's crossings? Is it available online, or in a book?

Neither. It was shown to me from a private source. The data came from compass course books that were kept. In the 1930s they were using a gyro compass to steer by, thus the ship would steer true courses. But they also recorded the magnetic headings in the columns for the steering and standard magnetic compasses and as well as their deviation errors.

 

[Michael Kestner]

That's a bummer.

 

[Lancastrian Navigator]

Sorry to reopen this (very) old thread, @Samuel Halpern , but having read through it a couple of times I've noticed the following inconsistencies:

The Olympic did not follow a single rhumb line course from one noon position to the next while on the great circle track to the corner. From detailed data that I looked at from several 1931 Olympic crossings, the logbook shows that they changed true course headings mostly about every 6 hours. (Sometimes as little as 5 hours or as much as 7 hours, but most changes appeared to be about every 6 hours or thereabouts.) This means they were changing course about every 3 degrees in longitude more or less. The distances between two noon positions along the GC track would therefore be less than the single rhumb line distance between the two noon positions because they tried to follow the great circle track fairly closely, more so than what I expected they would do. I believe this is why the distances recorded on those three log cards consistently resulted in a somewhat shorter distance to the corner than what those straight rhumb line distances would give.

That is consistent with the methodology which I was taught by a Royal Naval instructor in 1977, recalculating the course from a fix or EP every four to eight hours. The chosen interval would depend on the speed of the vessel, between 15 and 30 knots, to make segments of ~120 miles. That appears to be completely in line with the 20(ish) knot Olympic altering course every six hours.

Since Capt. Collins brought up the Olympic maiden voyage distances, lets take the reported run for the second day as an example since we have the starting and stopping coordinates from her log to work with, and therefore, we don't have to assume anything.

Starting coordinates were 50° 22'N, 19° 17'W. Ending coordinates were 47° 51'N, 32° 20'W.
Using Meridian parts we get a rhumb line distance of 535.652 miles (which rounds off to 536 miles) as Capt. Collins showed. (This result can easily be obtained from several on-line java scripts for those interested in doing so.)

Now let's use the mid latitude method to find the rhumb line distance.

What I did was 1st convert all degrees to minutes of arc.

Starting Lat coordinate is 50*60+22 = 3022' N
Ending Lat coordinate is 47*60+51 = 2871' N

Starting Lon coordinate is 19*60+17 = 1157' W
Ending Lon coordinate is 32*60+20 = 1940' W

The difference in latitude, dlat = 3022-2871 = 151' which is also the distance in nautical miles from north to south that the ship ran.

The middle latitude is the mean of the starting and ending latitude, or (3022+2871)/2=5893/2=2946.5' which expressed in degrees becomes 2946.5/60=49.11°

To get what is called the departure (east-west) distance in nautical miles, we first take the difference in longitude, dlon = 1940-1157 = 783'

and then multiply by the cosine of the mean latitude. This gives us 783*cos (49.11°) = 512.58 nautical miles in westward steaming.

We therefore have a southward distance 151 nautical miles, and a westward distance of 512.58 nautical miles using this method.

The total distance run is then found by taking the square root of the sum of the squares, or sqrt ( 151^2 + 512.58^2 ) = 534.36 nautical miles.

The difference in milage between the two methods is 535.62-534.36 = 1.29 miles.

By the way, the log card of the Olympic listed the run for the 2nd day as 534 miles. I got 534.36 which rounds off to 534. Meridian parts gives 535.65, which rounds off to 536.

Using this mid latitude method as described above, I get a distance for the 3rd day's run of 541.54 miles (which rounds off to 542 miles). The log card listed 542 miles. Meridian parts gives 542.681, which round off to 543.

Finally I got a distance from that noon to the corner of 173.22 miles, while meridian parts gives 173.616 miles.

Whereas the above calculations take a single segment of over 24 hours (being between apparent noons when steaming west) rather than four shorter ones, in line with the practice used by both Olympic's officers and me.

The difference from what I did and what Capt. Collins did in the mid lat calculations is that he used a "mid-lat correction" factor to get an adjusted number for the departure distance. He claims that this would be consistent with 1912 practice, and that is where I have to differ.

Let's look at the data.

For the run posted for June 17:
Log showed 534, I got 534.36 (534), Capt. Collins gets 536.675 (537)

For the run posted for June 18:
Log showed 542, I got 541.54 (542), Capt. Collins gets 542.719 (543).

Another example, take the rhumb line from noon June 19 (41-33N, 54-47W) to noon June 20 (40-41N, 66-50W):
Log showed 548, I get 547.2 (547), by meridian parts you would get 549.260 (549).

Take Voyage #2 westbound on rhumb line from noon Jul 17 (41-15N, 57-26W) to noon Jul 18 (40-35N, 68-49W):
Log showed 518, I get 517.7 (518), by meridian parts you would get 519.671 (520).

So is is clear, at least to me, that the method used by those officers working out the distances on the Olympic were not worried about such things as mid-lat correction factors in computing the middle lat. This is not even mentioned in Bowditch. Is is likely that they used transverse tables to get their results which require some interpolation of the data to be performed. I doubt they would have bothered to use a mid-lat correction factor even if they had those available.

In any event, the values that I obtained using the mid latitude method as I described in detail in the above post of Thursday, July 5, 2007 - 5:26 pm, produce results which agree quite nicely with the distances recorded in the log. To me, that is what counts.

Without the precise details from the logs which you were shown, I would have to make assumptions to calculate the exact distances by mid-lat of a four segment daily run. Given that caveat, I would still expect them to be closer to the Olympic's recorded figures than the ones determined from a single rhumb line per day with only a noon course change.

That, of course, implies that many of the discussions about Titanic's actual route (and especially the distances made good) need to be revisited as they are probably quite a few miles in error.

David.

 

[Lancastrian Navigator]

Unlike practicing mariners, we enthusiasts have domestic activities to distract us from our navigation. I've only had chance to do the first of the four segments for the day's run considered in the previous post.

Given the information presented in this thread, RMS Olympic was in position 50°22·0'N 19°17·0'W at 13:17:08 GMT on 16 Jun 1911 (12:00:00 ATS).

On a course of S77°W (257°T) for the next 6h 32m 20s, Olympic would have reached a DR position of 49°52·0'N 22°35·3'W at 19:30:11 GMT (18:13:03 ATS) having made good 133·5 NM at an average of 21·47 knots.

I'll try to get the other three segments done during my lunch break and after work tomorrow.

 

[Lancastrian Navigator]

From 49°52·0'N 22°35·3'W at 19:30:11 GMT, on a course of S74°W (254°T), Olympic would have reached a subsequent DR position of 49°15·2'N 25°52·8'W at 01:43:14 GMT having made good 133·5 NM at an average of 21·47 knots.

At this point, Olympic's ATS would be set back by 52 minutes 12 seconds from 00:26:06 to 23:33:54 to align with ship's solar noon on 17 Jun 1911.

 

[Mike Spooner]

Whilst on the subject of Olympic crossing. Did captain Smith face an icefield on his last crossing with Olympic before Titanic?