target speed: the eighty-ten method

[greyrider]

target speed, the eighty_ten method
in this tread im going to be introducing to all of you a technique
from the TFCM, and from the realm of imaginative tactics, that which is characterized by
or bearing evidence of imagination.
so if you want to advance your target speed determinations, to an advance level, your probably
going to have to pass threw this post, because no one has done this before, no one has shown this before, and the beauty is
it works great.
"
about a year and a half ago, i opened a tread called: "target speed, seaching for the magic bullet".
and in that thread i talked about a particular angular setup between a target and a submarine, and that if
this angular setup could be maintained, the AOB becomes predictable, and it didnt depend on seeing the target,
in fact the target could be at the maximum listening range of the hydrophones.
so with a closing target being held at a constant bearing, with a known AOB, the targets speed can be determined by using the
submarines speed.
the only tools i used on the submarine to determine target speed is:
submarine hydrophones (just listening and keeping target on bearing)
submarine knotmeter ( adjusting sub speed to keep target at constand bearing)
submarine timepiece (not really needed if target is held constant, but TFCM likes to time it for 2 to three minutes)
combat information mod for TM 2 (has the data to rate a targets speed versus sub speed)
and math formula: St= So*sin LA / sin AOB

where:
ST = target speed
LA = lead angle
AOB= aob of the target


By null at 2010-08-01


By null at 2010-08-01


By null at 2010-08-01


By null at 2010-08-01

whats not used are maps, plots, radar, sonar pings or ship length.
altho i have a movie to show you, its about an hour and one half long, i cant seem to find a site
to upload the movie to, filefront only accepts vids that are less than 2gb. the movie has 15 parts, each part has about has almost 4 gb,
so i cant even upload it in parts.
this movie shows the submarine holding a closing target constant on an 80 degree bearing,
with a ten degree aob, the submarines speed is 2 knots, so at the bearing and aob, the targets speed is 11 knots.
this speed was determined while the target was over 19nm away, and it took the sub almost 1 1/2 hours to close on it,it was hit with
all three torpedoes fired at it.
what i can do is give you the mission to practice with, i can give you the combat information mod for TM.
the combat info mod has two new charts, one has the data for the 8010 method, and the other is a chart for torpedo offsets, that is,
taking out two or three targets simultaniously, but i really need to make a handbook for the mod first, which explains how to use the charts and graphs.
so ill try to get that up later on, right now this is all im going to say about it.

[TabbyHunter]

That...is a very great tactic. You didnt make it yourself, did you?

[Rockin Robbins]

Now you have to demonstrate how you can determine AoB visually or any other way from 19nm! That is a stretch because they are well beyond the horizon at that point. If you're going to find the AoB by radar, then you might as well shoot by it and eliminate all the hocus pocus. I see smoke and mirrors here.

Since you cannot determine AoB from extreme range and you cannot determine target speed, your equation becomes a two variable expression with many solutions, not one. I don't think the problem is insolvable, but you're not there yet.

[greyrider]

continuing with the discussion on the 80-10 methed, one could ask, "how do you know your closing target aob is 10 degrees after leading it by 80 degrees".
theres only one way, and thats if the targets bearing remains contant at the 80 degree lead angle.
one thing i am seeing about this angular arrangment is that im begining to think of it as a reference bearing and lead angle, and that you can find the true aob
of the target, even if the target does not remain on a contant bearing.
for instance, take a look at this and see something, what if you set up this angular problem, and no matter how much you adjust the submarines speed,
the target will not remain contant. if that happens, thats a good indication the the aob is not 10 degrees.
this example asumes the target has a starboard aob, this is the same example used in this original post. now if the aob of the target is not 10 degrees,
no matter what, the target is going to advance in bearings,
in my original post, i held the target constant at bearing two eight zero, so it had a 10 aob.
what if it has an 11 degree aob, or more, well you will still certainly close on the target, you will see it when it comes over the horizon, and it will
still be a ninety or near 90 target track, but it wont be good for a accurate speed estimation
but watch this:
using the formula SS x sin LA / sin AOB
where:
ss = sub speed
la = lead angle
aob = target aob
watch what happens when aob other than 10 degrees are present on the target.
ask the sonar man the targets bearing a speed, he will usually tell you a few facts about the target such as bearing, closing moving away, slow med, or fast speed.
medium speed is from 8 knots to 11 knots.in the op, the target held contant at 280, sub speed keeping target constant was 2 knots, so target speed was 11 knots.
if the taqrget cant be held constant, aob is not 10 degrees, it could be more so, at
11 degree aob, plug in formula, do the math,
for an 11 degree aob, sub speed at 2 knots, target speed is 10.3 knots, still within medium speed tolorance
for a 12 degree aob, sub speed 2 knots, target speed is 9.7 still a medium speed.
for a 13 degree aob, sub speed same, target speed is 9.0 knots
14 degree aob everything the same, target speed is 8.3 knots. still within the medium speed tolorance, but as you can see, as the aob increases, the targets speed is decreasing,
so now if you try to plug a 15 degree aob into the formula, your target speed is now 7.8 knots, and now is below medium speed and would be rated as slow speed by the sonar man.
now you know that your target has anywhere from a 10 degree aob to maybe a 15 degree aob, if your sonar man rated the targets speed as medium.
now its just a play with numbers, or maybe a little mapping and plotting to find the targets real speed.
so from this angular settup between target and submarine, you can get either an extremely accurate speed estimation, or one very close.
more to come later.

[Pisces]

I'm sure we are all very curious about your video. But I'm pretty sure we are not waiting to download 60 Gigabytes!! for it. Surely there must be a way to compress it.

Your idea has merrit, however I think fixing your mind on a target AOB of 10d and a target speed of 11.3 knot if your sub is going 2 knots, well ... is just a too special case to be usefull in practise. If you manage to get the bearing to target steady over a long period, then you only know you are in pure intercept. However he could just as easily have had an AOB of 30d when moving at 4 knots. Or have 20d AOB when moving at 6 knots. And add to that the possibility of the target moving away, so the AOB could also be towards his rear.

Sure, you say, but the hydrophone operator can tell us what speed range he is in, or if he is moving away rather than closing to us. That helps narrowing it down. Well I really doubt if that could be done so quickly as in the game, the instant he hears it, or that he really could be so sensitive in real-life. What do I know, I have no real naval experience, I just find it hard to believe.

And I also would like to pose the question, how slow is constant? How long do you wait before you consider the bearing steady enough?

Let's generalize your idea. Because I certainly can see a use for it.

First of all, no need to fix your lead angle to 80. The sound on the 90 or 270 bearing is good enough, and get's that last percentage of use out of your speed. You can't expect the AOB to be near 10 degrees so why expect that you'll be crossing his bow perpendicular (which is what I expect you're expecting )

So, now I assume you set course to beam the sound bearing, so sound on 90 or 270. Now make a record of the starting position. Very important!!! Now, set whatever speed you need to keep that bearing steady. That means accelerating and decellerating a bit as the bearing changes 1 degree forwards or backwards. Since you are perpendicular to the sound you automatically will do this with the least speed neccesary. Avoiding excessive noise. Do not turn your sub but keep it steady on course. Eventually you should still have the bearing on your 90 or 270 after a long time. Infact you could do this the entire time until you are about close enough to fire. Now you figure out your average speed during this time, which could be really accurate if you do it right until the end. You've moved a certain distance over a certain time and calculate with whatever tool the average speed(authentic with a nomograph ) Ok, you may ask, but then I need to measure with the Super-Duper-GPS-Map-localiser. Surely that is not realistic. No, you are right in that, .... but ships can have a very simple speed measurement system that counts the revolutions of a small propellor as it flows through the water, known as a speed-log. If it is connected to a tachometer then you can sum up all revolutions and get a distance. Give or take a bit current-drift, but let's assume that to be equal to both vessels. Atleast, that's how I make it credible to myself.

Ok we measured our average speed, with the bearing kept steady, thus approximately in pure intercept. Let's now assume he has an AOB of 90 to the sound bearing (for lack of anything better), so we think he is going parallel to us. He probably is not, as he is probably faster and closing, but the rest of his speed is now pointed along the bearing and we can't measure that. But we do not need to either. He may come as quickly as he wishes, infact the quicker the better.

We are in pure intercept, but we want a torpedo to be in pure intercept.

In comes the intercept formula:

sine(ownsub_leadangle)= sine(targetAOB)*targetspeed/ownspeed

or how we are going to use it as torpedo-equivalent:

sine(torpedo_lead)=sine (assumed_targetAOB=90)*assumed_targetspeed/torpedospeed

Now you have enough data to setup the shot. Or feed the TDC. Assuming he is on a imaginary course perpendicular to the given bearing, and so appearing to move at the same speed as we did. (that's as much as a Blind's Man intercept can tell) And eventually being on top of us, so just a matter of waiting not too long with firing because of arming distance.


I'm not saying this is accurate, because you have no idea how far he is, so if you fire too soon you're probably going to miss. (As objects in the distance look much smaller angularly than when they are near) Also, the gyroangle is probably significant and you need a range figure to correct for parallax aiming error. But if you let him get close enough his length makes him vulnerable anyhow. Anyway, the geometry of the speed triangle should be correct. What you are really interested in is matching the speed vector components that are perpendicular to the bearing, so inside the triangle, as in this image:



You just have to have patience when matching your speed to the steady bearing, and hope your batteries last that long.

[Rockin Robbins]

If you let him get close enough you don't need the mumbo jumbo. And just because you are on a collision course does NOT mean his AoB is 10º. As Pisces said, it could be just about anything. The only thing we know is that it is under 180º! We do know whether it is port or starboard also.

I'm coming up with a brainstorm but I can't quite put my finger on it. Pisces' diagram is the beginning of it though...

The only problem is that I'm coming up with another visual or radar technique, at least partially. You do have to know whether the torpedo can reach and you really should shoot well under 2000 yards for your average merchie.

Once I get my software back in order I'll work on it.