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Old 05-31-2020, 03:22 AM   #1
Vantskruv
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I wonder, do the convoys always zigzag?
Hence, I am practicing the 4-bearing method, while moving, and the calculations seems to be correct when I am crosschecking (in this example, the approximate bearing 4 crossed the expected point of my course, which should tell I have done things right to that point, and after have determined the convoy position and course, I checked that the lengths between every bearing was the same, which they where).


In the above example, the calculations told me the convoy had the course of 310 degrees, with the speed of 12 knots, and distance to them where about 16.6km from where I measured the bearing 4.
Setting up an intercepting course (planning to flank ahead of them and place me for a 90 degree attack), I spotted them too early with the UZO, as if they had a much lower speed. Also, when spotting them (about 45 degrees port side), I spotted a destroyer aswell almost twelve'o'clock, seeing him turning his stern against me (I think). Hence their course seemed to not be as I expected...


I wanted to continue to play, but I had to close the game (whished there was a save feature in this game).


Either, my calculations was very wrong, or they where affected by the convoy zigzagging, I am not sure which.

Picture of my calculations:

https://drive.google.com/file/d/1X8l...ew?usp=sharing

Last edited by Vantskruv; 05-31-2020 at 03:34 AM. Reason: Cleanup
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Old 05-31-2020, 05:45 AM   #2
derstosstrupp
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I believe they are guaranteed to zigzag on hard setting. The zig leg times are random, as are the degrees.
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Old 05-31-2020, 09:51 AM   #3
Pisces
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Quote:
Originally Posted by Vantskruv View Post
...
Either, my calculations was very wrong, or they where affected by the convoy zigzagging, I am not sure which.

Picture of my calculations:

https://drive.google.com/file/d/1X8l...ew?usp=sharing
Not necessarily so. The drawing is done in correct fashion. I think your tactical choice of increasing speed along the same initial heading might have been your undoing in getting a reliable fix on it. Getting closer to the target again won't help getting an accurate fix. If you look at ABRG4 and BRG4 they are pretty much the same heading. So, even if showing a graphical intersection, it's position is meaningless. You need a clear crossing, ideally perpendicular. The resolution provided by the periscopes or even the hydrophone does not allow such 1-degree resolution. (technically the TDC dials and compass allows it to be down to a 10th of a degree, and map tools can draw angles with decimals, but accuracy errors add up if you do) If you look at the (range dependent) course lines (A1, A2) across the 2 circles (C1, C2) you used to make the predicted 4th bearing (ABRG4), the general target course could be considered to be close to 130-135. Once you established those you should have chosen to turn in that direction, surface for greater speed (if you did not already) and sprint along the generally parallel course. This would have provided a more clearer intersection of ABRG4 and BRG4, resulting in a more reliable target position and resulting from that a more accurate target speed.

This method is based on difference in drift-rates of the sound/visual bearings. As such you want your speed to initially either not contribute to the relative motion across the line of bearing (which it didn't when you moved slowly along bearing 1) or to contribute as much as possible by moving across a bearing, fast and (for increased effect and to the extent it is known) retrograde with regard to the target course. In the second phase you want to do the opposite of the first. Which to choose first is a gamble. By going slow and along the initial bearing you decided to let the target tell it's direction. Which is fine. As you get to know more, and you are unlikely to force premature detection. But as it turned out, the bearings started to drift slower (measure the differences between the bearings). If the drift of bearings slows down the AOB (at bearing 2) is larger than 90 and you are getting behind it. So once this is known it would have been prudent to restore a position more forward to the target. So to surface and run on diesels for additional overtake speed.

Then there are two choices for the new own course to take to increase that bearing rate and catch up. If the general target course is been established (as you have: 130-135) then turning parallel to that would solve the catching up part. But being somewhat behind would cause your range to decrease first ( as you near the target beam/AOB 90) and risk putting you in danger of detection since you don't know it's actual range yet. Especially in fog conditions this can get you caught with pants down. How much of a daredevil are you, or do you want to play it safe?
If you decide the latter, then turn perpendicular to the last bearing. It is clear right then what heading that is. It is not dependent on drawings or calculations. So immediately executable as first approximation. You can be sure you will not decrease range from that point, at least not on your own account. As you will be going faster and AOB was larger than 90 indicating opening target range. How far can you let it go until you loose the signal/sight? If it was faint (required high gain) to begin with the parallel course might have been more prudent. By moving perpendicular to the bearing the drift will also be as large as possible at the beginning. Whether that is enough depends on your choice of time interval. As it takes a bit of time to rise to surface, and dive again if you need to use hydrophone to locate it. Your average speed will decrease from that.

Last edited by Pisces; 05-31-2020 at 10:29 AM.
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Old 05-31-2020, 11:37 AM   #4
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And for those that want a TL/DR: (you loose so much additional consideration by ignoring it)

A higher speed on a course that already does not contribute much to bearing drift will not help much more to separate the angle between approximated and actual 4th bearing. Turn to use your speed across the other side of the line of bearing.

P.s. Vantskruv

The position you take the bearings at isn't important to be on a line or at regular distances. So don't worry about the exact spacing or alignment of V1 and V2. You need to keep accurate times of taking bearings and where. (if they are unequal you can correct for them but makes the drawing more complicated.) BUT you DO want to mark your position when you take them. Moving on a steady course and using the odometer distance since a last fix/turn can help with that.

I do not understand the red check in section 2 of your description entirely. Checking a point against a length does not make mathematical sense. I think you mean the crossing of ABRG4 on your own track to point of BRG1? (which would require you can't turn between B1,B2,B3. A self imposed limitation, but not required for the method/drawing to work)
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Old 05-31-2020, 11:40 AM   #5
Vantskruv
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Thanks @derstosstrupp.
And thanks @Pisces for your thorough answer!


I have made some measurements, and indeed the little differences between the approximated bearing 4 and real bearing 4, makes it really hard to get the correct position of the convoy (in my example one degree of measured difference would change the targets course by about 10 degrees, and reduce their distance from ownship to the half!).



Though, I have been thinking about changing the course after measuring the bearing 3, as you told! But I ignored it as I thought changing the speed would be enough, and being afraid that calculations/measurements would have more errors because it is harder to approximate your position after a course and speed change, as I did the measurements on 30m depth without surfacing (playing safe).



I will reconsider, and try to implement course changes, and see if that, even though ownship position maybe a little more off, I may get a more precise result than only changing speed (hence, it is better to strive for the bigger difference between approximate bearing 4 and real bearing 4, while sacrificing approximation of ownship position?). I just need to figure out the turn radius of different speeds of the ship, both submerged and surfaced, and also if the speed will change while turning. Maybe it is not too hard to approximate/calculate your position after a turn after all, and that would beneficial.



Also, a theory of mine, I guess the 4-bearing method is more used at longer ranges, and I guess you may get better results if at long range, than close range. I am not sure what I am basing that of, it is just a hunch.

Last edited by Vantskruv; 05-31-2020 at 11:50 AM.
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Old 05-31-2020, 11:47 AM   #6
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@pisces
The red sentence in my explanation is written wrong, thanks.
And you understood it correctly:
Checking if the crosspoint of ARBG4 and CRS is at the point O+V1*3 on CRS.


I made this for myself just to understand what is going on.
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Old 05-31-2020, 12:07 PM   #7
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Quote:
Originally Posted by Vantskruv View Post
Thanks @derstosstrupp.
And thanks @Pisces for your thorough answer!


I have made some measurements, and indeed the little differences between the approximated bearing 4 and real bearing 4, makes it really hard to get the correct position of the convoy (in my example one degree of measured difference would change the targets course by about 10 degrees, and reduce their distance from ownship to the half!).
Yes, and not only course, but also the position shifts rapidly along those lines.

Quote:
Though, I have been thinking about changing the course after measuring the bearing 3, as you told! But I ignored it as I thought changing the speed would be enough, and being afraid that calculations/measurements would have more errors because it is harder to approximate your position after a course and speed change, as I did the measurements on 30m depth without surfacing (playing safe).

I will reconsider, and try to implement course changes, and see if that, even though ownship position maybe a little more off, I may get a more precise result than only changing speed (hence, it is better to strive for the bigger difference between approximate bearing 4 and real bearing 4, while sacrificing approximation of ownship position?). I just need to figure out the turn radius of different speeds of the ship, both submerged and surfaced, and also if the speed will change while turning. Maybe it is not too hard to approximate/calculate your position after a turn after all, and that would beneficial.
I wouldn't worry so much about your exact position when taking the bearings. Especially in the beginning. When learning this try it in the tutorial mode, where the ship does not turn, and you get the correct solution to prove you results. (first move away some 20 km to make this a bit more representative) Use the nav-bot to provide you with positions even when underwater (though not continuous, but incrementally). It is more useful to learn when to speed up or make a course change and in what direction to get the geometry to work out well. And definitely try to go to the surface. You speed is 3 times larger than max submerged. And about twice the common merchant speed. The further your bearings are apart, the less your position errors matter.


Quote:
Also, a theory of mine, I guess the 4-bearing method is more used at longer ranges, and I guess you may get better results if at long range, than close range. I am not sure what I am basing that of, it is just a hunch.
Well, at long range you have little else than your hydrophone and plenty time and room to manoeuvre to do so. At visual range you can also do it, and more precisely so with the periscope. But then you can also make direct use of the AOB and distance observation. So there are other methods that get quicker results. Even if the bearings change more quickly at shorter range. But it is also more likely to get suppressed submerged to avoid detection.

Last edited by Pisces; 05-31-2020 at 12:32 PM.
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Old 06-01-2020, 06:38 PM   #8
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Empirically speaking, Hard convoys appear to zigzag on average by 15 degrees every 15 minutes, but the deviation from this average can be quite high, especially for the exact timing of zigzags.

Since a typical 4-bearing takes around 15 minutes, its utility is rather limited when facing a Hard convoy. You are much better off using Eyeball Mk1 as well as any and all techniques that do not require a prolonged period of observation.

Another practical implication is that you are well advised to time your attack to occur right after a course change (but not before the convoy settles on it properly) to minimize the chances of a whiff due to a random zigzag after torpedoes are in the water.
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Old 06-01-2020, 11:59 PM   #9
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Regarding measuring accuracy, it is said according to some historical TMA documents that it's better doing a lead-lag maneuver than a lag-lead, which means you can run parallel with the target at the beginning (usually observing a relatively low bearing rate), and then increase the bearing rate later by turning and lagging the target. The goal is to maximise the difference between the approximated 4th bearing and the real 4th bearing.

But it may not place you to a suitable position for attacking.

Speaking of the plotting, I personally likes to go creative using the draw-from-midpoint tool in Wolfpack, like this: https://www.subsim.com/radioroom/showthread.php?t=240883.

Last edited by ljqcn101; 06-02-2020 at 12:08 AM.
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