Greenwich Time

[B-rad]

Perhaps someone can help me with this. I am looking for the Greenwich time, purely (and I stress purely) based on Titanic's wreck site (aka boiler field). I have looked up several ways of calculating this, and I don't know if any are correct. So below is my calculations. Thanks.

NY is 5hrs behind Greenwich


Titanic wreck is 49° 56.8W

49/15 (degree of arc in 1 hour) = 3.3 (.3x60= 18)

- 3hrs 18 min Greenwich, + 1hr 42min NY


OR


49x4= 196/60 = 3.26 (.26x60=15)

- 3 hr 15 min Greenwich, + 1hr 45min NY



For the 56.8 I keep coming up with around 3 minutes. I defiantly don't know if I'm doing this right, so forgive me. The site I found states 20 min W is 1/3 a degree (which means there are 60 degrees), and there is 1 degree every 4 minutes. So 4x60/3= 180 or 1 min & 20 seconds. For Titanic I did

60/56.8 = 1.1

4x60/1.1= 218.2/60= 3.6

.6x60 = 36

So 3 minutes 36 seconds



Which means (I'm leaving off the seconds)

- 3hr 21min Greenwich, + 1hr 39min NY

or

- 3hr 18min Greenwhich, + 1 hr 42min NY



Hope I did this right, if not, hopefully someone can learn me good! If so, which way is more accurate?
Obviously these times don't correlate with either the 1hr 33min, 1hr 50min (though pretty close to this one), 1hr 39min nor the 2hr 2min time differences for NY time, stated in various texts. Again, I'm just basing the time off the wreck site, so perhaps this is not a good site to reach any of these times.

The sites I used are:

Astrology: Calculating the Chart - Greenwich Mean Time GMT

https://www.quora.com/If-it-is-12-n...n-the-following-longitudes-69°E-30°W-and-12°E



Thanks again!

 

[Jim Currie]

Hello Brad.

You should refer to the time at any place as being so many hours and minutes FAST ....AHEAD of GMT or SLOW...BEHIND GMT.
Places East of Greenwich are FAST of GMT. Those to the WEST are SLOW of it. Thus Eastern Standard Time is 5 hours SLOW of GMT. Actually, Mariners did not use EST for Navigation, they used GMT and they also used a New York Time which was 4 hours 55 minutes SLOW of GMT, not 5 hours SLOW of GMT. Eastern Standard Time is an arbitrary choice for reasons other than navigation.
EST was/is used by ships when they entered east coast ports. Otherwise the clocks on board ship in port were/would be 5 minutes faster than local time which has been standardised and bears no relation to the actual longitude of the place.

The sun crosses 15 degrees of longitude every hour and a meridian(line) of longitude every 4 minutes of time. Additionally: 60 seconds of time = 15 minutes of longitude. This means that local time at the longitude of Titanic's wreck is a fraction under 3 hours, 19 minutes, 48 seconds. SLOW of GMT. Therefore when it is Noon at the wreck site, it is already almost 3-20pm at Greenwich.

Hope I made this clear?


Jim C.

 

[B-rad]

LOL. We must have been posting at the same time for as soon as I was about to hit post yours popped up. Thanks, it does help and it confirms the time I found. Below is my new post.

So I did some other calculations, based on the longitudes given on Pg. 78 of Sam Halpern's 'Report into the loss of the SS Titanic: A Centennial Reappraisal'. The coordinates are:

44° 31 W (Titanic's noon position for April 14th)

56° 22W (Titanic's projected noon position for April 15)

The calculations are:

44x4=176/60=2.93
.93x60=56

2hr 56

31x4=124/60=2.1
.1x60= 6

2 min 6sec

Equaling 2:58

56x4=224/60=3.73
.73x60=44

3hr 44min

22x4=88/60=1.5
.5x60=30

1min 30 sec

Equaling 3:45

These times match Halpern's times, and are 47 min apart, which takes into account the time change. These corrdenates also lead to 2hr 2min time ahead of NY.

This leads to a second question... When redoing my last calculations for Titanic's boiler field: 49° 56.8

49x4=196/60=3.26
.26x60=16

3 hr 16min

56.8x4=227.2/60=3.8
.8x60=48
3min 48 sec

Equaling 3hr 19min

This gives us a 1 hr 41min difference from New York, or a time difference of 21min between Sam's 2hr and 2 min. Can we explain these minutes? Would Titanic have drifted 21 minutes worth of time? Or (for kicks), lets say the time difference is the fabled 1hr and 50 min from New York, which still leaves us a 9 min. difference, would Titanic have drifted a 9 min difference?

With a current of 1.25 (GLTS | Collision Point), in 2hr 40 min Titanic could have drifted 3.44 nautical miles SE. I don't know how much this would change the time, if it would at all.

Of course these questions don't take into account how far Titanic drifted to a stop or traveled after striking the iceberg, as we don't know how long it took Titanic to drift to a stop, or how long the engines were put ahead or reverse after the collision.

I want to make clear, that in no way saying Sam is wrong, or trying to attack his wonderful work. In fact having the coordinates written in his book helped me understand the math better. I just want to try and understand these differences.

Thanks!

 

[Jim Currie]

The times used by Sam check out fine. I disagree with is Noon 15th Longitude but for this purpose it makes no difference.

When Titanic sank, her Watch Keeping clocks (bridge) would register the time set on them. This time would have nothing to do with where the ship sank. They would have been 2 hours and 58 minutes or 3 hours and 22 minutes SLOW of GMT depending on whether a partial clock change had or had not taken place before impact.

The difference of 21 minutes you refer to is the difference between the time showing on the ship's clocks ( apparent time at ship) according to Sam and the actual mean time of the location where the wreck lies. Because Sam does not subscribe to a partial clock change,the first time is the time for longitude 44º 31 West and the second at 49º 57'West. When Titanic hit the sea bed, her clocks would show a time of either 2 hours 58 minutes SLOW of GMT or 3 hours 33 minutes SLOW of GMT. Current or actual longitude would have nothing to do with it I don't believe there was such a current, anyway

Jim C.

 

[Alex F]

NY is 5hrs behind Greenwich

If one counts from Greenwich.

Look at the map and find a reference point!

All ports had different local time

BR
Alex

 

[Samuel Halpern]

Brad,

The simplest way to convert longitude to what is called Local Mean Time (LMT) is first to convert the longitude to decimal degrees, then divide by 15 to get decimal hours, and then convert decimal hours to hours, minutes and seconds east or west of GMT.
e.g., From Ballard, the longitude to center of boiler field is 49° 56' 49'' W = 49° 56.817' W = 49.947° W.
Now 49.947/15 = 3.330 hours = 3 hours 19 min 48 sec behind GMT.
But LMT has no real bearing on time kept at sea back then because ship's were carrying Apparent time. Apparent time takes into account the exact time when the real sun reaches the local meridian of the vessel. When that happens, clocks if set properly, should read 12:00. Assuming Titanic was precisely at 44° 31' W at local apparent noon April 14, the time difference from GMT would have been 2 hours 58 min 29 sec. If you do the conversion to LMT as above for that noontime longitude you will find a 25 second difference. That has to do with what is called the equation of time, the difference between the position of the real sun and the fictitious mean sun used for LMT and GMT calculations. The equation of time just happened to be close to 0 around April 16.

 

[Jim Currie]

A lot easier using the Haversine Tables, Sam. That's how they would have done back in 1912.

Jim C

 

[B-rad]

Thanks everyone (Jim, Alex & Sam) for your help. Jim, it took me a second to understand what was meant by, " Current or actual longitude would have nothing to do with it..." But I got it now & makes total logical sense. They set their clocks at the time changes done at or around midnight to reflect the apparent noon of the following day (with a slight adjustment if needed at noon as well). Therefore the clocks, if set to be 2hr and 02min ahead of New York, after the adjustments made at 12am April 14th, would remain 2hr & 02min ahead regardless of where the ship was. Only the time adjustments made at midnight the 15th would alter the time, if they occurred, but only to reflect the apparent noon of the 15th. The clocks weren't adjusted every hour to reflect their current position.

I am carious as to where you, Jim, think the noon position for the 15th would be. If there is a thread in which this was discussed, feel free to just point me to it.

Thanks again

 

[Jim Currie]

Hello Brad.

Glad to be of assistance.

You declare : "I am carious as to where you, Jim, think the noon position for the 15th would be.".

I think that if the weather had remained calm until Noon 15, Captain Smith and Co would have been very pleased with the performance of Titanic. She seems to have been averaging 22.5 knots after 8pm on April 14 without any increase in engine rpm. This means that on a course of 265 True, she would have increased her westerly Longitude by about 30.3 minutes every hour and her latitude would have decreased by about 2 minutes every hour.

At ship time Midnight on April, 14 it was 15d-02h-58min. GMT. At that moment, first adjustment would be made and the clocks would be set back 24 minutes as the first part of the planned clock change. At that same moment ,the bridge clock would show 11-36 pm and the date would still be April 14 for Log Book entry purposes. Four minutes later, at 11-40pm adjusted time for Log Book April 14th, impact took place. At that moment the GMT would be 15d- 03h-02min

Now at Noon ship time April 14, the equivalent GMT was 14d-14h-58 minutes. Since Captain Smith planned set back the ship's clocks by 47 minutes between ship Noon April 14 and Ship Noon April 15, he obviously planned for a run time between these two Noons of 24 hours 47 minutes. If we add that run time to the GMT time of Noon, April 14 we get the estimated GMT of Noon for April, 15, 1912. It is 15d-15h-45 minutes. To arrive at my idea of the position for Noon, April 15, I subtract the GMT of the moment of impact from the estimated GMT for Noon April 15. This gives me a run time at 22.5 knots from a position 1 mile north and 1 mile west of the Wreck site. I use that start point because that's where I think Titanic hit the iceberg. I do not subscribe to a south-setting current. Here's my calculation:

Arguments: Course 265 True. Speed 22.5 knots. Run time 12 hours 43 minutes.

Impact position: Latitude 41-45.0' North..............Longitude 49-56.0' West.

D. Lat. 25.4' South....D. Long. 6-25.0' West

April 15 Dr Noon position, Latitude 41-19.6' North.Longitude 56-21' West..

I believe that Captain Smith expected Titanic to be at about the longitude of 56-15' West and to average a speed of about 21.7 over the day's run.

Hope that helps.

Jim C.