Speed measurements/indicators


Georges Guay

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Ok Jim, I’m gonna give you my trick but don’t tell nobody. I was standing in the corner of the bridge by the very first window; remembering that I was docking the beast. I was then protected from the door wind draft in the same manner as the crow’s nest canvas windshield. As I am an expert with flies as being a sport fisherman, I lit up and pumped out vigorously a big stinky Malboro cigarette. But I must admit that there was a few on my PPU screen, keyboard and in my coffee cup. But they just add taste to that infect instant Nestlé coffee they serve. :)

Jim, if you divide the distance by the time between two celestial fixes, it gives the speed over the ground. It was a concept widely used at the time. They were probably using both method and compare them to find out if they had applied the proper current effect on the log. For daily average and general speed log inscriptions, they were using speed over the ground. If they couldn’t take any sights for days, they probably had to figure out a calculated speed over the ground derived from a current corrected speed in the water, compare to the average rpm/pitch/slip and or from previous voyages. If not, there would land up with large differences in day to day speeds which could have to be justified. Even in that era, I guess they were trying everything possible to keep away the office nose from the ship’s business.
 

Jim Currie

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Ok Jim, I’m gonna give you my trick but don’t tell nobody. I was standing in the corner of the bridge by the very first window; remembering that I was docking the beast. I was then protected from the door wind draft in the same manner as the crow’s nest canvas windshield. As I am an expert with flies as being a sport fisherman, I lit up and pumped out vigorously a big stinky Malboro cigarette. But I must admit that there was a few on my PPU screen, keyboard and in my coffee cup. But they just add taste to that infect instant Nestlé coffee they serve. :)

Jim, if you divide the distance by the time between two celestial fixes, it gives the speed over the ground. It was a concept widely used at the time. They were probably using both method and compare them to find out if they had applied the proper current effect on the log. For daily average and general speed log inscriptions, they were using speed over the ground. If they couldn’t take any sights for days, they probably had to figure out a calculated speed over the ground derived from a current corrected speed in the water, compare to the average rpm/pitch/slip and or from previous voyages. If not, there would land up with large differences in day to day speeds which could have to be justified. Even in that era, I guess they were trying everything possible to keep away the office nose from the ship’s business.
The method of navigating in 1912 was the same right up until RADAR became common on all merchant ships. That didn't happen until well after WW2. In fact, formal qualifications as a Radar Observer on UK Merchant ships did not come into force until mid to late 50s. That's when I got my first one (still have it).
In fact, the navigation on ships such as the Titanic was much more precise than on a lowly cargo vessel, because she had dedicated Navigators... officers whose soul purpose in life was to provide the Master with minute by minute updates on the ship's navigation. Every MN Navigator (myself included) used the Patent Log and we knew it's error at any time throughout the voyage. On Titanic, it was read and the reading recorded every 2 hours throughout the voyage.
We know what the reading was at 6 am on April 14 and immediately after impact with the iceberg. It was 125.7 at 6 pm and 260 at the time of impact. This means she covered a log distance of 134.3 miles on her 265 True track from 6 pm until about 49-56'w. This in turn means that Titanic was at about 46-57 West...about 2,2 miles eastward of The Corner at 6 pm and at about 46-51.5'W ... 3.5 miles more to the East. at 5-50 pm when she turned . i.e. at least 5.7 miles east (and about 3 miles southward) of it. I'm sure you can calculate a position for where she turned.(and point out my errors)
The foregoing only holds good if you understand why 5th Officer Lowe was able to confidently state the speed was.."Twenty-one knots or under; it was really 20.95, about. If the speed had been increased or reduced during the interval when I was off duty, I would have been informed of it. " And you also accept QM Rowe's evidence that "As soon as the berg was gone I looked at the log and it read 260 miles.
 

Georges Guay

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In fact, the navigation on ships such as the Titanic was much more precise than on a lowly cargo vessel, because she had dedicated Navigators...
They were amongst the greatest dedicated ocean navigators in the whole universe, as they pretend, but they succeeded to deduce a 20 nautical miles soon corrected by a 13 nautical miles offset on their CQD positions, that located Titanic on the west side of the icefield!!! That's what we call precision ... :oops:
 
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Georges Guay

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What does mean 260 miles or 45 miles «over the water by patent log» between 8 and 10pm, when a vessel is steaming across chaotic eddies engender by the collision between the Labrador Current and the Gulf Stream?
 
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Georges Guay

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I sailed around Cape of Good Hope many times on board gigantic crude oil carriers. We had all the GPS, DECCA, Satellite Transit, you could dream of. On a few occasions, I got stuck in these colossal eddies without having real knowledge of them. None of these eddies are specifically shown on Pilot Charts. Nobody really knew their existence before NASA produced this visualization using NASA/JPL's computational model called Estimating the Circulation and Climate of the Ocean, Phase II or ECCO2.

The vessel was absolutely impossible to be kept on track. She was drifting from one side to the other very rapidly. My speed over the ground was going up and down. At the end of my watch I had to annotate the logbook with the miles run but in this case, I had to enter the vessel’s progression toward its destination during the course of my watch. I had such a difference with the other mates that the captain asked me later what happened, like traffic. I explained him; he smiled and never heard about it again.

So through eddies, how could you estimate any reasonable distance run over the ground with a patent log to find out where you are on a chart … if I didn’t have any idea of my distance run with all the electronics ? Just good luck !

P.s. My record is 6 miles off track in one hour while crossing the Gulf Stream abeam ... I can tell you that I did not earn a navigator medal that day!!! :)
 

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Jim Currie

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The only log readings given in evidence was 260 miles at the time of collision, and 45 miles run between 8 pm and 10 pm. We were also told the the log was reset at noon. That's the evidence.
Yes Sam, the only log readings actually stated were as you say, but you know very well that Lowe gave that precise speed when asked and that the only way he could have come up with such a speed was by dividing the patent log reading as noted on the Scrap Log by 6. Truth be known... you do not want to see this because it completely upsets the time of impact theory.
It is not good to ignore evidence or make a preferential selection. Lowe had no reason to make such an exact observation regarding speed except that he was being closely questioned on the matter of ship speed.
You have claimed in the past that Lowe's 162 miles to go from Noon to the 5-50 turn was a typo and should read 126 miles. In fact, if you calculate the GC distance, and subtract the distance already sailed to Noon from Fastnet Rock, you will find that the distance to go from Noon to The Corner was 124 miles , not 126 miles..
Would you be surprised to know that if you take the time to actually plot the evidence of Boxhall and Lowe, rather than dismiss it out of hand, you will find:
A ..That Titanic turned at a point about 6 miles on a bearing of 105 True from The Corner .?
B: That Captain Smith guessed this and altered course to 266 True to bring her back on the line at or near to 7-30 pm?
C.. That the patent log would be reading close to 162 at 7-30 pm

Boxhall did not alter course to 266 True... he found that the ship was on that course when he went on Watch at 8 pm. Only Smith would order such an adjustment and he would only do so if he believed his ship was south of the line.
According to Pitman, the ship was right on the line at 7-30 pm sights. Smith did not know where his ship was at 7-30 pm until well after 9 pm. If he did not order a course change before impact, then Titanic would have hit the iceberg north of the line.
 
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but you know very well that Lowe gave that precise speed when asked and that the only way he could have come up with such a speed was by dividing the patent log reading as noted on the Scrap Log by 6.
It seems he came up with that by dividing the distance the ship was from the corner at noon by 6 hours. Nothing to do with log readings unless they reduced rpms from 75 down to about 71 for six hours.
 
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Or try this one.
Suppose the log reading at 6pm was written down as 135.7 miles and Lowe read the 3 as a 2. That gives him a speed by log of 20.95 knots through the water. But the reality was that it was 135.7/6=22.6 knots, or a two hour average of 45.2 miles, which is in line with Hichens' 45 miles by log between 8 and 10pm. The ship was carrying 75 rpms all day.
 

Georges Guay

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If a vessel steers 266°T at 22.6K by patent log and there is a current setting to 196°T at 1.3K, the course and speed over the ground would be something like 263°T at 23.1K. :)
 
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So? It all depends how long you were in that particular current. If the the average current was setting 070°T at 0.5K for several hours earlier, then the course and speed over the ground would be something like 266°T at 22.1K during that period of time. No big deal. :)
 

Doug Criner

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Time out. This discussion reminds me of something from my ancient naval experience in an old destroyer.

There was something called a dead-reckoning tracer. It kept a graphical plot of own-ship's track along with target's track - very handy when maneuvering violently back and forth, attacking a submarine (not for plotting a steady course over time), and deciding when to turn hard left or right, and when to drop depth charges. So, where did the DRT get its dead-reckoning inputs? For ship's course, from the gyro compass. I can't remember where the speed input came from - maybe just from the engine rpms? Or from the engine-order telegraph? But, of course, ocean current was not important, nor was travel over ground! We were all about trying, or more like playing like trying, to kill someone.
 
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Georges Guay

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So? It all depends how long you were in that particular current. If the the average current was setting 070°T at 0.5K for several hours earlier, then the course and speed over the ground would be something like 266°T at 22.1K during that period of time. No big deal. :)
No big deal for sure … one has just to «cherry pick» one of the 32 compass rose points as a set, a unique force vector as a drift and an estimated period of time, to stretch a vessel’s position a on a chart where it best suit his own presumptions. And not only that, as set and drift is also subjective to lateral wind leverage and hydraulic forces acting upon a vessel.

Questions:

The lateral windage centroid of a tramp ship is located at the rear of her center of flotation. The vessel is located in the center of an ocean gyre where the current is zilch. She is steered by hand through a fresh breeze on the Port beam. Being steady for hours, in which direction the vessel may well set; up wind, downwind or no effect?

A tramp vessel is propelled by a left hand propeller. She is steered steady by hand for hours in flat calm weather. In which direction the vessel will tend to set; toward the Port side of the route, the Starboard side or no effect?

How can we determine by eyesight alone, no glasses needed in that case, if a vessel is drifting and in which general direction?

So, if someone attempt to deduce from the parallelogram forces law where a vessel will land from a magnetic steering compass and a patent log considerably influence by wind, current, time, lateral wind leverage, propeller transverse trust, the ability of her wheelsman, the accuracy or her quarter master to properly record the patent log register vs. time, the age of her master… he will soon find out that these influences can knock out all common rules into a meaningless cocked hat vectors structure!
 

Jim Currie

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If a vessel steers 266°T at 22.6K by patent log and there is a current setting to 196°T at 1.3K, the course and speed over the ground would be something like 263°T at 23.1K. :)
As you know, the Patent Log was not a speedometer, Georges... it simply measured the apparent distance that the device had been towed through the water. In theory, it is a little turbine. much like the turbine in a hydro plant. The device in question rotated 9000 times per mile of distance it traveled through the water i.e. the number of rotation were directly related to the speed of the water flowing past it. In theory, a head current would increase the pressure on the rotator blades and the rotator would turn faster. thus indicating a greater distance over the ground or water and consequently an exaggerated speed.
However, as a ship handler, you will know that the patent log normally is located in the neutral zone within the wake pattern. Consequently, the log error was normally very small. You might be interested to know that HMS Cumberland which was scrapped in 1959 (The year I got married), recorded an error of less than 5 miles over a voyage of 3000 miles.
 

Georges Guay

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Jim, you’re in command of a brand new passenger liner, on a great circle passage from Bermuda to the English Channel Light Vessel. The distance is 2,800 nautical miles. Your cruising sea trial speed is registered as 22 knots, in dead calm weather and no current whatsoever. The general average Gulf Stream current along the route is estimated at 2 knots by Pilot Book and the Weather Routeing agency forecasts light winds all the way.

Once on Full Away of Sea Passage, the perfectly rigged patent log starts reading, the Doppler Log Water Tracking push button is depressed and the GPS Distance Run Over the Ground is activated, so that all instruments starts reading and recording the distances run through the water and over the ground at the exact same time.

At End of Sea Passage, all instruments arrived at the same time or after 117 hours and are compared. Since everything went according to the voyage plan, the difference in distance between the patent log and the Doppler log water tracking is nada zero zilch! But compared to the GPS, it seems that something went wrong. The recorded distance over the ground is effectively 2,800nm but the distance run through the water from the patent log and the Doppler log is only 2,567nm or a difference of minus 233nm against the GPS.

On your way back, in the exact same conditions and route, the GPS still shows 2,800nm. The difference between the patent log and the Doppler log water tracking distances are still nada zero zilch. But now, it took 140 hours to cross and the distances recorded by both water logs are 3,080nm or plus 280nm against the GPS.

Eastbound Log (2,567nm) + GPS Difference (233nm) = 2,800nm
Westbound Log (3,080nm) - GPS Difference (280nm) = 2,800nm

The least we can say is that these results are absolutely astonishing, aren’t-they!!! How can that be possible?

Now Jim, do the same exercise only westbound but in that existing chaotic current system, while crashing into a few gales low along the run and under an overcast sky all the way through and tell me how you are going to manage to reach Saint George’s Cut by magnetic compass and by patent log alone. Please be advised that there are many hundreds of shipwrecks all around Bermuda Island … might is well you provide the lookout with a good set of glasses! :)
 

Jim Currie

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Georges, that was a saga worthy of Jules Verne or Captain Maryatt. However, you are not comparing like for like. I suggest you start with Difference Between GPS and DGPS and take it from there.
Incidentally your example tracks are way of "base".

You waffled -on about ocean currents around The Cape. You haven't lived, pal until you have taken loaded bulker or worse still, a light one through the Pentland Firth or the Messina Straits. Or for a real thrill... try the Corryvrecken.

As for the idea that the Labrador Current at the Titanic wreck site? I suggest you consult oceancurrents.rsmas.miami.edu/atlantic/slope-jet... If you do, you will discover that unless that particular current was turned-off during the month of April, 1912, there was no way that the Labrador Current could have flowed over warmer water in a southerly direction in the vicinity of 42 North, 50 West . I suggest you play the animation.
 

Georges Guay

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Jim, do you know the nautical adage; «When the pilot points to the leading lights … the cadet looks at the finger»? :)

My example was regarding a simple way I would adopt to make a cadet understanding the difference between the distance run through the water from the distance run over the ground of a vessel proceeding in a non-static liquid. You can change the current from a ¼ of a knot to Gulf Stream 6 knots, the final outcome will all proportions guarded be the same. But I understand that you could’ve forgotten the basics since your maritime academic degree, if you ever held any, was conferred since ages. Serving ashore as an insurance clerk would certainly not help either.

Jim, when you sailed back and forth through the Pentland Firth, the Messina Strait's, the Strait of Corryvreckan or the Niagara Falls, did you compare the patent log with your DGPS WAAS? Have you kept any «evidences»? How can you understand those distance run differences if you’re not even able to make the distinction between an Ocean Current from a Tidal Current?

Being almost always on the defensive, even about what might seem like the most insignificant things, bring some people to enjoy arguing just for the sake of arguing. ;)
 
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So, where did the DRT get its dead-reckoning inputs? For ship's course, from the gyro compass. I can't remember where the speed input came from
I would assume Doug that the destroyer had what was called an underwater pitometer log system. It works very much like an airplane's airspeed indicator by measuring the difference between dynamic and static pressure heads using a rodmeter which projects through the vessels hull in the forward part of the ship. They used that system on submarines as well to plot their DR course through the water even when submerged.
 

Jim Currie

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It seems he came up with that by dividing the distance the ship was from the corner at noon by 6 hours. Nothing to do with log readings unless they reduced rpms from 75 down to about 71 for six hours.
Your selectivity regarding the evidence of 5th Officer Lowe is astonishing, Sam. You pounce on his "15825. Did you look for any lights at this time at all.
Answer ...........-I glanced over in that direction casually and I saw a steamer there." and turned that "casual glance" into a swinging bow.
Yet you ignore the most obvious pointers as to how the man navigated between 6 pm and 8 pm. I remind you:
Senator SMITH.
In order to ascertain the ship's position accurately at 8 p. m. you must know her speed at 8 p. m., must you not?
Mr. LOWE.
If you take the average speed from 12 to 6 - that is giving her a run of six hours - she will not jump up in two hours, from 12 to 6 o'clock, from that average speed. You have six hours in there to take a mean on.
Senator SMITH. :But you had means, had you not, of ascertaining definitely how fast the ship was going?
Mr. LOWE: In what way, sir? We have the log -
Senator SMITH. (interposing) Between 6 and 8 o'clock.
Mr. LOWE.
We have the log.

I should think that it would be obvious - even to Long John Silver with both eye sockets covered, that Lowe was using Patent Log readings and dividing them by the time interval between them to obtain a speed to use in the calculation of Dead Reckoning positions.

It would be equally obvious to LJS that since Lowe did not arrive on the bridge until 10 minutes after Titanic was assumed to have been at The Corner, he could not calculate an 8 pm DR before he had calculated a 5-50 pm DR. The work would be in two stages. (It would be recorded on the "Day's Work" sheet.).
Stage 1: Course and distance from Noon to 5-50 pm using the known course and an estimate of the speed derived from the 6 pm Patent Log reading divided by 6. This would give him a DR for 5-50 pm
Stage 2: Course and distance from 5-50 pm to 8 pm using the same speed derived at 6 pm (because as Lowe thought "she will not jump up in two hours".
The foregoing is the reason why Lowe was able to the following answer:
Her speed from noon until we turned the corner was just a fraction under 21 knots.

Sam. you cannot ignore the foregoing or waffle around it with suggestions of Patent Log inaccuracies. The Bottom line is that Lowe got that speed from a reading of the Patent Log .The man would have been very particular about speeds, given that his main task that evening was the construction of Slip Tables. You are very much aware of that since, in the past,you have written extensively about the subject.
I can well understand your reluctance to accept this part of Lowe's evidence. After all, you have also written extensively about the question of time change, and if you accept the evidence of Lowe, concerning speed, you will have to go back to the drawing board.
 

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