SUBSIM Radio Room Forums - TARGET SPEED, searching for the magic bullet

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TARGET SPEED, searching for the magic bullet

i think i have found it, im working on it, may take a week and, it may take longer, but i made a mission to test
this formula from the torpedo fire control manual, using the procedure explained by the FCM, using just the hydrophones to determine target speed. it works like a charm,
i just need to test it alittle more at extreme hydrophone range, 18.9 nm. i wont post again, until i have it down pat, but as soon as i do, i will present it to you, in a post, and in a mission.

formula is:

SS x(sin LA) / (sin AB)
where
ss = sub speed
la = lead angle
ab = angle on bow

Are you defining lead angle as the bearing to target expressed in number of degrees from the bow, as in the German bearing system?

If so, you're onto something with some playing around. All by itself, it means nothing. BUT if you put yourself on a collision course with the target, that is the bearing to target doesn't change over time, THEN his speed is a known proportion of yours based on the Angle on the Bow. (unless his AoB is zero or 180, in which case the target speed is undefined)

I don't have my drawing software right here at work, but I could work it up and shoot you the diagram for you to troubleshoot the rest of the way if you'd like. You're onto something really useful here.:yeah:

Quote:

Originally Posted by greyrider

...
using just the hydrophones to determine target speed
...

SS x(sin LA) / (sin AB)
where
ss = sub speed
la = lead angle
ab = angle on bow

Isn't it a bit hard to determine the AOB with only your hydrophones :hmmm:
I don't know what kind of hydrophones you've got but mine only give the bearing

Ah well maybe its just an American superweapon for a change, the japs have got UFOs and such, so it'd only be fair if the US have got superpowered hydrophones:rotfl:

Uh DarkFish, it isn't nice to make fun of others. Especially when the ignorance is yours. Greyrider is on solid ground here.

I shall draw a mental picture and see if you can get up to speed here. With your sonar, you determine a bearing to the target. A simple ping will give you a range. Range plus bearing equals position. Plot the position. Three minutes later, ping again. Range plus bearing equals position number two. Connecting the two positions and extending in the direction of travel gives the target track. With the protractor, clicking ahead of the target position on the track, clicking again on the target position and a third time in the middle of your sub position, you can read the AoB right off the nav map. By inspection with the compass rose on the end of the ruler with help on you can read the target's course. The number of hundred yards between the two positions is the target speed in knots. No superweapons, UFOs, or cute puppies were harmed in this procedure.

Note that the target speed is not necessary to derive the course or AoB. Greyrider is working out another way to determine the speed without plotting two positions 3 minutes apart. I can see this being useful for a visual target where you could use his Mark 1 Eyeball method of measuring AoB. Greyrider is brainstorming here on the message board, and the number one rule of brainstorming is that wacky ideas are encouraged and enthusiastically followed up to see where they lead. We whack people who make fun of ideas over the head with a belaying pin.
http://i196.photobucket.com/albums/a...ys/one_bat.gif

Yes, RR, that is how you can get the track of the vessel and formulate the AOB relatively accurately :up:

Quote:

Originally Posted by Rockin Robbins

With your sonar, you determine a bearing to the target. A simple ping will give you a range.

Yeah i can see your point
My previous post indeed sounds a bit diminishing, it wasn't meant that way.
If anyone feels hurt I'm sorry for it.
I just thought Greyrider meant using passive sonar only (hydrophones is passive sonar only, isn't it, or am I completely wrong here:-?)
Using passive sonar only it'd be completely impossible to determine AOB.
But now that I understand what he is meaning I can definately see the use of this formula, it'd be a very accurate and easy way of determining the targets speed.
So keep up the brainstorming and don't mind about people like me joking about UFOs:up:

I just smell progress here. Even if an idea turns out to be positively lousy, often it leads to productive directions. Just ask Ducimus. Oh, you can't.

I just found this...I just asked the basic same question in another thread. I've been trying to figure out how to track aob and speed with sonar.

I would ping, mark bearing and range on the map. I don't know if the 3 minute rule applies or not, but ping again at 3 minutes, mark on the map range and distance.
My speed is zero and don't see how it can be done if your sub is moving.

I just didn't know if this rule worked to determine speed. Now I see it's easily possible to get AOB.

Course the problem is TF...ping, and it's a new ball game. If you get this figured out, someone please sticky it.

You can do it if you are moving, but you need to do some vector addition. Most easily accomplished if you are moving at a constant speed along a straight line.

Quote:

Originally Posted by DarkFish

Quote:

Originally Posted by Rockin Robbins

With your sonar, you determine a bearing to the target. A simple ping will give you a range.

It's NOT impossible to determine AOB with passive hydrophone listening. It maybe not a quick thing to do. And being stationary simplifies alot (just like sckallst mentioned) But certainly possible. Look to the following thread:

http://www.subsim.com/radioroom/showthread.php?t=110619
(further down the thread are links to a video)

Or if you want to take a shortcut for such a drawing with a handheld tool:

http://www.subsim.com/radioroom/show...0&postcount=14

(or this one, works the same, but linear as opposed to the circular above:
http://www.subsim.com/radioroom/show...0&postcount=10)

i havent worked on it for two days, been busy. but i mean passive sonar, its always passive sonar with me, with pinging, you might as well surface, call a cab, and tell them where to pick you up.
when i first heard of the early war theory of the us navy, i was very intrigued , i believed it was possible, and there had to be some substance to it,
otherwise it would not have been brought up.
my mission has always been to prove the us navy was right, i just dont think they had enough time to develope the concept, i have had years of sh playing to develope it, and i think i have done that in alot of ways.

guys it does work. i made the mission , and i did get the target speed , but i did reverse engineering, i already new the course of the target, and i had measured aob from the editor with my GTA 5-2 12 COORDINATE SCALE AND PROTRACTOR,
that i still have from the u s army.
i just wanted to test the formula, it works, i have that mission, i could upload it for you if you want to try it
i believe i placed the target 9. something nm away from the sub.
it only take seconds to get target speed using this formula, once you have the bearing constant, which is alittle difficult, because of the speed telegraph of the sub.
but i did it, and i know it can be done, and the TFCM says it can be done, so who am i to doubt them.
i have not tried from max hydrophone range yet, but my theory it using this formula with the point and shoot method, because of the 80 degree offset thing, once the target is there and constantly there, speed is no problem with this formula.
this is the best thing about sh i think, always trying out new concepts, this is what i love about the game the most., the war is over for me, i made it to 8/16/45, i wont start another career, for the rest of the time, im going to emmerse myself in the TFCM,
and bring to you if i can, what i can get from it .
rock, go for it, make the diagram, ill try to get the mission out, the one from long range as soon as i can, but i will add the mission that i first tried it on, it will be on filefront in about 5 minutes, if you want to add what you observe, by all means, do it.
ill call the mission formula test
also rock, you nailed it, the lead angle is from the bow of the sub, to the bearing of the target, good job buddy!

i had some problems uploading to filefront, but its up there now, you can use any one of three files, that say formula in it, as of yet, it wont let me delete any two at the moment, and there all the same, so you can use any of them

There were many plotting tools that the US Navy had in WWII that we do not have available to us: bearing rate plot, bearing difference plot, stadimeter plot, slide rules up the wazoo, etc. Technically, with the bearing rate plot and bearing difference plot it was possible to compute relative course, but not range from passive sonar or visual information. However I have not found a single incidence where this was ever done during the war.

For those interested, the relevant parts of the Submarine Torpedo Fire Control Manual:

Quote:

561. BEARING RATE PLOT

As was explained under the duties of the Navigational Plotter we usually plot true bearing and ranges to determine the target's true course. If this is done on a maneuvering board we get target relative course and speed.

Now if we substitute for actual range a relative or abstract range we will get the direction of the relative movement line of the target (or relative target course). It can be proved mathematically that:

r = square root (K / (db/dt))

It is obvious that it would not be practicable to

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CONFIDENTIAL SLM 1
actually compute the various values of relative range during an approach. We can, however, assume a convenient value for K which is a constant and construct on a large maneuvering board a graph on which we can plot values of rate of change of bearing (db/dt) against true target bearing. Plate IX is a picture of such a plotting sheet in which K = 200

Plate X is a set of data which has been recorded by the Sonar Plot Recorder. The numbered lines are the actual sonar bearing of the target at 30 second intervals. The data which are plotted by the sonar plotter are the differences between bearings one minute apart and the mid-bearing from the recorder sheets For example, the first db/dt is 2 1/4 degrees plotted at true bearing 330 1/2 degrees. The mid-bearing from the recorder sheet say not be the exact mathematical mean of the two bearings but it is close enough for practical application. These values represent the rate of change of bearing db/dt, for a dt of one minute and the average true target bearing during the period for which the rate has been computed. These values are shown plotted on Plate IX and indicate that the relative course of the target is 120 degrees T. Since Plate IX is also a maneuvering board we may lay out the own course and speed vector of 000 degrees T, 3 knots, and transfer the relative course line to the end of the vector and for a target speed of 15 knots obtain a true course for the target of 110 degrees T.

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CONFIDENTIAL SLM 1
This method of obtaining the target's course is obviously laborious and subject to sonar errors and arithmetical errors of the plot recorder. In obtaining the target course by this method there are several points which should be remembered:

a. Even though each change of course by the target will produce a new relative motion line they will not be connected in such a manner as to produce a plotted track of the target.

b. Since the errors in the present JT sonar can be as much as plus or minus 1 to 2 degrees the value of db/dt which are plotted will vary considerably and the best that can be expected is a relative motion line obtained by "fairing" in the plotted points.

c. The inherent errors of the sonar system render it impracticable to plot values of db/dt of less than 2 degrees/mm.

d. Although a dt of one minute is used in the example smaller values may be used to obtain more plotted points without changing the graph itself or the answer desired. Experienced plotters will ordinarily use a value of dt = 30 seconds. This value of dt, however, cannot be changed during a problem.

e. The method will not work if continuous bearings are not available. Bearings obtained at intermittent intervals are of no practical value.

f. One erroneous bearing will cause two plotted points to be in error.

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CONFIDENTIAL SLM 1

g. When the target changes course an immediate change will occur in the rate of change of bearing (db/dt) and tile the change of course is in progress it will change at a varying rate which will continue until the target is steadied on its new course.

562. BEARING DIFFERENCE PLOT:

The Bearing Rate Plot as has been shown plots a varying amount of bearing change occurring over a fixed time interval. The Bearing Difference Plot plots a specified amount of bearing change occurring over a varying time interval. In the Bearing Difference Plot as in the Bearing Rate Plot the result obtained is the relative course of the target. (a) Plate XI is a Bearing Difference plotting sheet using a scale factor of twenty. The mathematical proof of this method is long and involved and will not be discussed. The formula used in the construction of a bearing difference plotting sheet is Tan B = X Tan A in which B is the angle between the Y axis and any radial line; A is the bearing difference angle and X is the scale factor. In Plate XI the tangent of angle B = 20 X tan 0.5 degrees or

Tan B = 20 X .0087
Tan B = .174
B = 99 degrees

In like manner radial lines representing each 1/4 degree of bearing difference are laid out up to 5 degrees.

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CONFIDENTIAL SLM 1
Beyond this varying difference angles are used as desired. The time scale used has no effect upon the solution obtained. A scale which will facilitate accurate plotting should be selected. It can be seen that increasing the scale factor will decrease the value of the minimum value of bearing difference which can be plotted for a given size of plotting sheet. When the rate of change of bearing of the target is large it will be found that a plotting sheet made up for a scale factor of ten or fifteen will give better results. Plate XII is a plotting sheet made up using a scale factor of ten.

The procedure for using this plot is as follows:

1. Start the stop watch on any even degree of bearing.

2. Label the Y axis as the reciprocal of this bearing.

3. Note the stop watch time and plot a point each time the bearing changes 1/4, 1/2, 3/4, etc., from that which obtained when the watch s started.

4. When enough points have been plotted to establish a line, measure the slope of this line. In Plate XI this is done by transferring the line to the origin and reading value of the slope on the vertical or horizontal scales around the maneuvering board plot. In Plate XII it is done by placing an overlay scale on the line as shown and reading the value directly.

5-47
CONFIDENTIAL SLM 1

5. Apply this slope to the value of the Y axis determined in step 2. If the true bearing is increasing the slope is negative. If the true bearing is decreasing the slope is positive.

6. This is then the true direction of the target relative motion.

7. On the mooring board combine this value with own course and speed and known or estimated target speed to determine true target course. Each time the target changes course it is necessary to repeat again steps one through six.

(b) Plate XIII is a set of data plotted on Plate XI and labeled one (1). In this example the true bearing of the target was 000 degree T increasing. The "Y" axis is then 180 degrees T and the slope is 8 degrees. This gives a value of 172 degrees for the true direction of relative target course. This is then plotted on the maneuvering board to give a true target course of 171 degrees T. Note that the target changed course at 6 minutes and that points plotted at 06-15 and 06-17 indicate a definite change in the slope of the line. All changes of target course will be indicated in this manner.

(c) Plate XIV is another set of data in which there is a much larger rate of change of target bearing. This is shown plotted on Plate XI and labeled two (2). Note that a slope has been determined in 1 minute and 42 seconds. In the example the initial true bearing of the target was 010 degrees T increasing.

5-48
CONFIDENTIAL SLM 1
The "Y" axis is then 190 degrees T and the slope is 50 degrees. This gives a value of 140 degrees T for the true direction of relative target course. This data is then plotted on the maneuvering board to give a true target course of 132 degrees T.

It can be readily seen that it is inconvenient to plot in the lower left hand corner of the plotting sheet. This can be prevented by using a plotting sheet made with a smaller scale factor. A second method is to double the time scale. The line labeled three (3) in figure XI shows the data of line two (2) plotted with the time scale doubled. Note, and this is important, that changing the time scale does not change the slope of the line.

It is sometimes desirable to plot bearing differences against equal increments of time instead of the method used in step 3 of the procedure. This does not vary the result and allows more points to be plotted with very low bearing rates.

(d) comparison of the Bearing Rate Plot and the Bearing Difference Plot as shown in the examples brings out the following points which should be noted in selecting the method to be used.

1. The greatest advantage of the Bearing Difference Plot over the Bearing Rate Plot is that bearing inaccuracies inherent with the sonar equipment are absorbed resulting in smaller and smaller percentage errors as the plot progresses.

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CONFIDENTIAL SLM 1
The Bearing Rate Plot uses bearing rates computed between one minute observations. The effect of the error of the sonar equipment for any given bearing rate will remain the same. In the Bearing Difference Plot this is not the case as the plotted values are always taken from a reference bearing. As the problem progresses the bearing difference becomes larger and larger and the percentage error becomes smaller and smaller.

Due to the inherent errors of our present sonar equipment the Bearing Rate Plot is not usable with a bearing rate less than 2 degrees/minute, The Bearing Difference Plot may be used at rates less than 1 degrees/minute.

As our sonar equipment is improved both plots will of course become more effective.

2. In the Bearing Rate Plot no data are available before an elapsed time of 1 minute. In the second example of the Bearing Difference Plot twenty-eight (28) points were plotted and a solution obtained in an elapse time of 1 minute, 30 seconds.

3. In the Bearing Rate Plot one bad bearing affects two plotted points. In the Bearing Difference Plot a bad bearing affects only one point.

4. In the Bearing Rate Plot a recorder and complicated arithmetic computations are required to obtain data. These are of course subject to error. In the Bearing Difference Plot no recorder is required and the data

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CONFIDENTIAL SLM 1
is obtained directly from the sonar bearing repeaters by observation.

5. In the Bearing Difference Plot where the angle on the bow of the target becomes larger than 30 degrees the slope of the line becomes very critical and a slight error in picking off the slope will introduce a fairly large course error. However, as the angle on the bow increases the target course becomes less and less critical in the fire control solution as the optimum torpedo track is approached.

Have at it and have fun!

RR and Greyrider are talking about two different things. Even if both are from the same manual.

RR is describing early forms of TMA based on rate of bearing change. in essence this is the same as the method of TMA described by Aaron Blood in his MoBo and by mittelwaechter with his method.

This method that RR is talking about predates ekelund ranging and whatnot and will only provide relative course (note not true course, unless you are staionary), not speed or range.

Greyrider's formula that seems to work is nothing other than the necessary result of basic trigonometry. This formula has by other names been very well known in this community for years already. it is simply that knowing your own speed as one leg of the triangle, the bearing to target and the aob of target, the target speed makes the other leg.

Hell you can even do it without a constant bearing with one of these, but then you do need at some point in the process a range.

http://www.subsim.com/radioroom/show...ighlight=iswas

@joegrundman: I'm not convinced you're right, joe, because how do you know the AoB if....:hmmm: But IF you did know it you're right, it's a basic trig function. Good to have a real modern sub jockey as a backup.

I'm sure now that greyrider is looking for something he can actually use without knowing anything that he couldn't find out using the passive sonar. Relative course is the info he needs because that translates directly to AoB, just like target track can translate into AoB.

I'm not convinced that the mathematical gymnastics will make it a practical tool for SH4 players, but I"m just like greyrider, always looking for another angle, but unlike you, without the advantage of direct knowledge of modern techniques. Maybe we can cobble up some PDF WWII authentic bearing rate plots and bearing difference plots. A spreadsheet could perform the math song and dance without stepping on its shoelaces. It's just a very interesting problem that's caught my imagination.

the reason why i think this could work so well at very long range is because at long range the aob is going to be very small, less than 10°, and that would be the best time to make the calculation, and once the speed of the target is known, or approximated, matching up bearings to target at
the speed you calculated should bring you very close to the targets relative course, over time. but speed is more important than course here, because even if your playing auto tdc, once target direction has been established, its very easy to drive your sub into a 90 target track angle.

in the formula test mission thats now up on my filefront page, if you try it, use a target aob of 20° in the formula, i think i kept the target bearing constant at bearing 291°, and own ship speed of 5 knots,
the target speed in the formula test mission is 12 knots, lead angle was upper 60's, cant quite remember because i took subsequent readings also, as the aob got deeper.
in my estimation, the hydrophone max range in sh4 is 18.9nm. even in the formula test mission, at 9nm, the target aob was only 20°, or near 20°, so i would be looking for a very small aob at long range, it could even be less than 10° at that range.

anyway
target speed is the mission is 12 knots
sub speed was 5 knots, when the bearing of the target changed, i increased or decreased speed to keep the bearing constant, i took other readings as the aob increased, to test my estimation of aob by hydrophones.
lead angle is from the bow of the sub to the bearing of the target.
what skill needs to be developed is estimating aob by sound, target diection is easy, but finding a number for aob might and is alittle harder but not impossible, even if target speed is off by a knot or 2, estimating the time of arrival
at your calculated speed into your visual ao, would tell you if your speed calculation is accurate or not, if target arrives too early( earlier than your estimation), its going alittle faster than your calculated speed, the reverse if its arrives later than you thought it would
theres always ways around things, we just need to always be flexible in our thinking, and make adjustments if we have to.

if i learned anything from sh about sub warfare, its that precision is not mandatory,
just being close is good enough, in most of the data we need except for speed, that has to be pretty close to precise.