Bismarck at DS after the second turn

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northcape
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Re: Bismarck at DS after the second turn

Post by northcape »

Antonio Bonomi wrote: Thu Nov 22, 2018 10:43 am

First I think we need to agree about the fact that talking about bearings and distances, ... the difference between navigational range and gun range in this case will be, ... given speed, course and relative distances, ... in the range of 0,5 degrees, … so well below the +/- 1 degree tolerance as far as the bearing goes, … and below the 1.000 yards every 10 sea miles for the distances, … so inside the tolerances I was proposing and that seems to be acceptable as far as I have read above.

Comments and an agreement about the tolerances I think are needed at this point.

As outlined before in more detail, I disagree on the tolerances of the bearings. Given the fact that the reading error in the best case maybe is +/-1 degrees, and that we have to account for the unknown gyrocompass calibration (and different unknown calibrations at each ship), I would be more conservative and suggest +/- 5 degrees as long as we don't know more about the settings of these instruments in 1941.

Also, in the quoted paragraph, there is a comparsion between gun ranges (or navigational ranges transverse to course directions) and bearings in that direction. I don't understand how this should be compared, e.g. an error in a gun range is perpendicular to an error in the directional bearing towards the target (if we are talking about bearings to targets). Further, how do you translate gun ranges to errors measured in degrees?
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Alberto Virtuani
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Re: Bismarck at DS after the second turn

Post by Alberto Virtuani »

Hello everybody,

while I agree with Antonio and Mr.Jurens about the selected set of "first class" evidences/documents and with the chosen "starting point" at 6:00 (milestone), in order to merge information and build a battlemap,

regarding tolerances, as already said, they may vary depending on instruments: when taken by a lookout hand binocular the tolerance may be even up to +/- 5 degrees (much less if the binocular is fixed and has degrees marks mounted on its pedestal), when taken by fire direction instruments, or recorded by the TS there is no space for larger than 1° tolerance.

However, even the "visual" lookouts bearings can be considered as subject to tolerances only when they are not cross-checked: in case a bearing X is reported by British and the exact reciprocal bearing Y (= X-180°) is reported by Germans at the same time, then no error is probable and the two bearings have to be accepted as simply "perfect".


Bye, Alberto
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Re: Bismarck at DS after the second turn

Post by Antonio Bonomi »

Hello everybody,

@ Bill Jurens,

I think we have agreed to use mainly British official inputs for the British own tracks and timings and similarly the official German inputs for the similar German information.

In this regard the German open fire timing is more than demonstrated on the German side official documents.

The main events timings on both sides being well inside the agreed 1 minute tolerance is clearly demonstrated by the correct report of British open fire at 05:52-53 on the German side ( perfectly in synch ), by the 05:57 fire on Hood correctly reported on both sides, and by the Hood explosion at 06:00 perfectly reported on both sides too.

I know there are many incorrect time inputs on both sides on many documents, but we need to have timing milestones agreed and respected, and those are the ones I am proposing too.

Consequently the German squadron opened fire at 05:55, as reported on all the German Official documents.

Bye Antonio
In order to honor a soldier, we have to tell the truth about what happened over there. The whole, hard, cold truth. And until we do that, we dishonor her and every soldier who died, who gave their life for their country. ( Courage Under Fire )
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Re: Bismarck at DS after the second turn

Post by northcape »

Coming back to the tolerances of bearings, I think there is still the misconception that the only error is a reading error. This is not correct. Even if your reading error would be zero, your bearing would still be wrong (or not perfectly accurate). Why? Because the instrument where you take the bearing from (the gyrocompass) has inherent errors, e.g. it does not provide the true azimuth relative to geographic north.

You can find a lot on the web on that, e.g. here: http://navyadministration.tpub.com/1422 ... ror-77.htm

In essence, the gyrocompass errors (not the reading errors) need to be corrected from astronomical observations. The higher the frequency of the observations, the better the error will be corrected. Also, the error grows fastest when traveling south-north or north-south.

This error is not relevant when you consider one ship over a short time only, as it will just be one systematic shift to all observations (=rotation of the track). However, as soon as you tie two or more ship tracks together by their absolute bearings to each other, it becomes very important as each ship will have its own systematic gyrocompass error.

Now how large this error can be expected to be for the situaton in 1941 in the DS, I don't know. Any insights/comments are welcome.
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Alberto Virtuani
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Re: Bismarck at DS after the second turn

Post by Alberto Virtuani »

Hello everybody,

again, the "inherent errors" of the instruments (as well as the reading errors) are a very real and interesting topic.To the gyrocompass errors we can add also the on board chronometers precision (that we have discussed some years ago already) regarding timings.

However, if we are really interested in reconstructing the battle, then we must realize that we often have reciprocal bearings (or timings) taken from both sides and these bearings (timings) match perfectly. Thus we can logically assume that there is no error at all in these cases and that we can lightly ignore any "inherent" error in the instruments on board of the ships.


Bye, Alberto
"It takes three years to build a ship; it takes three centuries to build a tradition" (Adm.A.B.Cunningham)

"There's always a danger running in the enemy at close range" (Adm.W.F.Wake-Walker)
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Re: Bismarck at DS after the second turn

Post by Antonio Bonomi »

Hello everybody,

since we will be mainly covering distances and mostly the relative bearings taken visually, ... below the 16 sea miles close to the horizon line, ... starting from the smoke and after looking at the enemy warships, ... I think it is wise to see the real situation on board being used by the spotters.

Here you have Able Seaman Alfred R. Newall on board the HMS Suffolk patrolling the Denmark Strait during that operation :

https://www.alamy.com/on-board-hms-suff ... 71320.html

I like you all to focus on the plateau below his binocular marked with RED arrows :
Suffolk_spotter_Newall.jpg
Suffolk_spotter_Newall.jpg (47.02 KiB) Viewed 1631 times
with that fixed reference available to read the bearing angle we can assume +/-1 degree tolerance with a very good confidence level.
Surely his reading compared to his warship course was very accurate.
If his warship was precisely on the reported course, is another story and another tolerance.

On board Prinz Eugen they were having the same type of instruments :
PG_spotters_Brinkmann.jpg
PG_spotters_Brinkmann.jpg (31.95 KiB) Viewed 1631 times
from the original Prinz Eugen Rheinubung film :

https://www.youtube.com/watch?v=pPmkOtSveXY

Bye Antonio
In order to honor a soldier, we have to tell the truth about what happened over there. The whole, hard, cold truth. And until we do that, we dishonor her and every soldier who died, who gave their life for their country. ( Courage Under Fire )
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Re: Bismarck at DS after the second turn

Post by dunmunro »

Antonio Bonomi wrote: Sun Nov 25, 2018 8:42 am Hello everybody,

since we will be mainly covering distances and mostly the relative bearings taken visually, ... below the 16 sea miles close to the horizon line, ... starting from the smoke and after looking at the enemy warships, ... I think it is wise to see the real situation on board being used by the spotters.

Here you have Able Seaman Alfred R. Newall on board the HMS Suffolk patrolling the Denmark Strait during that operation :

https://www.alamy.com/on-board-hms-suff ... 71320.html

I like you all to focus on the plateau below his binocular marked with RED arrows :

Suffolk_spotter_Newall.jpg

with that fixed reference available to read the bearing angle we can assume +/-1 degree tolerance with a very good confidence level.
Surely his reading compared to his warship course was very accurate.
If his warship was precisely on the reported course, is another story and another tolerance.

On board Prinz Eugen they were having the same type of instruments :

PG_spotters_Brinkmann.jpg

from the original Prinz Eugen Rheinubung film :

https://www.youtube.com/watch?v=pPmkOtSveXY

Bye Antonio
No, we cannot assume +/-1 degree accuracy. The scale under the binoculars appears to be graduated at 5 degrees per marking and there is the issue of taking bearings on a ship at sea via unstablized sights . 3rd the timing of the bearing and the timing of the entry into the log can vary considerably placing great uncertainty on the bearing's accuracy at time of entry into the log. This is from Sufolk's report:
0553 (B). Heavy gun flashes bearing 185°. Half a minute later Bismarck opened fire to port.
The bearing given is an approximation and the time given is not accurate either, if we are using Hood's open fire time as our timing reference.
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Re: Bismarck at DS after the second turn

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Alberto Virtuani wrote: Sun Nov 25, 2018 8:14 am

However, if we are really interested in reconstructing the battle, then we must realize that we often have reciprocal bearings (or timings) taken from both sides and these bearings (timings) match perfectly. Thus we can logically assume that there is no error at all in these cases and that we can lightly ignore any "inherent" error in the instruments on board of the ships.
If this is the case then I agree. But it would be good to see a table with reciprocal bearings and according times, and how small or large the discrepancies are (both in times and bearings).
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Re: Bismarck at DS after the second turn

Post by northcape »

dunmunro wrote: Sun Nov 25, 2018 5:51 pm
No, we cannot assume +/-1 degree accuracy. The scale under the binoculars appears to be graduated at 5 degrees per marking and there is the issue of taking bearings on a ship at sea via unstablized sights .
If this is the case then indeed the reading accuracy cannot be expected less than 2.5 degrees. If an higher accuracy would be expected (even at perfect visbility and calm sea), then the instrument would have a more finer marking, e.g. every degree.

I've done my fair part of surveying with optical instruments, and on a well-stabilised platform (terrestrial) you might can estimate the accuracy of a quarter of the tick mark spacings after many readings. But it is completely different on a moving/shaking platform.

Again, we are only talking about reading error, not the additional instrument calibration error yet.
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Re: Bismarck at DS after the second turn

Post by Byron Angel »

northcape wrote: Sun Nov 25, 2018 6:15 pm
Alberto Virtuani wrote: Sun Nov 25, 2018 8:14 am

However, if we are really interested in reconstructing the battle, then we must realize that we often have reciprocal bearings (or timings) taken from both sides and these bearings (timings) match perfectly. Thus we can logically assume that there is no error at all in these cases and that we can lightly ignore any "inherent" error in the instruments on board of the ships.
If this is the case then I agree. But it would be good to see a table with reciprocal bearings and according times, and how small or large the discrepancies are (both in times and bearings).

Keep in mind that the value of a reciprocity of bearings assumes that both were taken at the same moment in time.

B
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Re: Bismarck at DS after the second turn

Post by Antonio Bonomi »

Hello everybody,

do not even try to tell me that Suffolk did not have the 1 degree accuracy on the bearings.

It is enough to read her reports :
0447 (B). Enemy bore 186°, 15 miles, course 220°, speed 27-28 knots and bore 196° at 0456 (B).

0520 (B). Enemy bore 203°, 15 miles, possibly increasing speed; and shortly afterwards altered course 30° to port and then back to starboard.

and

0600 (B). Enemy bore 208°.
The bearings were not rounded with the +/- 5 degrees estimation.

This is a fact.

Bye Antonio
In order to honor a soldier, we have to tell the truth about what happened over there. The whole, hard, cold truth. And until we do that, we dishonor her and every soldier who died, who gave their life for their country. ( Courage Under Fire )
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Re: Bismarck at DS after the second turn

Post by dunmunro »

Antonio Bonomi wrote: Sun Nov 25, 2018 8:12 pm Hello everybody,

do not even try to tell me that Suffolk did not have the 1 degree accuracy on the bearings.

It is enough to read her reports :
0447 (B). Enemy bore 186°, 15 miles, course 220°, speed 27-28 knots and bore 196° at 0456 (B).

0520 (B). Enemy bore 203°, 15 miles, possibly increasing speed; and shortly afterwards altered course 30° to port and then back to starboard.

and

0600 (B). Enemy bore 208°.
The bearings were not rounded with the +/- 5 degrees estimation.

This is a fact.

Bye Antonio
Some bearings were probably taken via the DCT (or other) stabilized sights, however there is still the issue of timing; the bearing probably reflects an earlier time than the time of entry into the log or the time of transmission of the radio message. Is this a bearing on Bismarck or a bearing on the centre of Lutjen's squadron?
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Re: Bismarck at DS after the second turn

Post by Antonio Bonomi »

Hello everybody,

@ Dunmunro,

we have agreed to re-construct here in this forum ( I already did it years ago and I am continuously improving it in real time on a very large scale ) the Denmark Strait battle field scenario based on the available and agreed evidence.

It is obvious that we have to do it with the available evidence and that we have to accept the agreed tolerances in bearings, distances, timing, course, speed, ... etc etc, ... because the accuracy on the data on 1941 is not comparable of what for example we can have today.

Your concerns are correct, but again we do not have that level of precision usually, ... just few times, ... like for the Norfolk taken bearings at 05:53 on the Plot where Bismarck ( BB ) is on bearing 275° and Prinz Eugen ( Cruiser ) is on bearing 272°, confirming the Bismarck was following the Prinz Eugen.

We have mainly visual bearings and RD/F bearings, and I think that the +/- 1 minute tolerance on the time we should have agreed at this point is sufficient to establish with a good level of precision where the warships where one to another.

To really do this work it is necessary to start and put the main tracks and milestones on the paper, and after work on placing patiently one after the other the evaluated inputs we do have, ... and the whole scenario will come out pretty easily and nicely and will discover the real situation at sea among the all 6 warships that morning.

We will discover the correct and the incorrect inputs and sometimes we will be in front of a choice to decide what to believe, ... like to possible truth, ... or the impossible input in front of us.

That point is where the disagreements will arise and where our moderator role is going to become crucial, and I am confident that given his knowledge and competence it will be fairly easy to decide what to trust and move forward toward the historical truth.

Nobody wants to rewrite history or offend anybody, ... the historical truth about a 77 years old naval battle is what we are looking for.

Bye Antonio
In order to honor a soldier, we have to tell the truth about what happened over there. The whole, hard, cold truth. And until we do that, we dishonor her and every soldier who died, who gave their life for their country. ( Courage Under Fire )
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Re: Bismarck at DS after the second turn

Post by pgollin »

.

Simple look-out mounts are NOT going to give you bearings with +/- 1-degree accuracy, +/- 2.5-degrees is much more like it.

--------------

Re. "navigational" range versus gun range, the idea of "navigational" range is in itself rather odd. That SEEMS to imply the range as derived from a chart, rather than the actual distance, is that correct ? IF SO, then there are three distances, actual range, "navigational" range and gun range. IF that is correct then "navigational" range will suffer from the problems of time against plotting. Even if the various clocks involved were correct to within a second, the times recorded versus the time of the actual bearings/ranges taken are NOT going to be correct with the recording of the readings/time also adding to small errors intrinsic in the process.

One of the reasons for the RN's automatic plots was to try to give as much "real time" recording for decisions to be made.

Later in the war the British found that with centimetric radar there were times when the radar range to a target could vary as the radar beam bounced back off different portions of the superstructure.

-------------

As for Gunnery Reports. FOR THE RN, a departmental report (e.g. gunnery, engineering, radio (inc radar)) would normally to approved by the Captain, and then would be formally submitted to the Captain and separately to the Director of the Gunnery (or other) Department, and sometimes others e.g. relevant Fleet staff officer, Home Port commander or gunnery/maintenance staff officer, DNC, etc.... They would NOT be sent to the First Sea Lord (or other directly) that would be a matter for the Fleet Commander (using the Captain's report) or the Director of the relevant Department raising a particular issue.

.
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Re: Bismarck at DS after the second turn

Post by Byron Angel »

All of the range/bearing data under discussion here will be subject to some sort of inaccuracy. The real question is: to what degree would any such inaccuracy, in practical terms, affect a reasonable and rational narrative of events?

B
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