The Bearing Rate Course Finding method

[Munchausen]

Originally Posted by Nisgeis

When stationary and tracking a target, the point it will be closest to you will be when the target's AoB is 90 (port or starboard) as that is the point at which its position on the track is the closest to your position.

Not always. Say the target cuts across your bow at about a 45 degree angle. It will be closest when on (or near) the bow and will be further away when AOB reaches 90.

[Diopos]

Originally Posted by Munchausen

Not always. Say the target cuts across your bow at about a 45 degree angle. It will be closest when on (or near) the bow and will be further away when AOB reaches 90.

The minimum distance between a point A and a line is AB, B being the point where a Vertical -passing through A- cuts the line.


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[Pisces]

Well, you wanted an equal-bearing interval method, so this one is not what you want. It's a slide-rule for the 3-bearing equal time interval method. You can still do the same, but it's just a different variable you are measuring. I'm not sure if you were allready aware of it. I think you do. Oh well,

http://www.subsim.com/radioroom/showthread.php?t=147719

(This is the SH3 thread, I also made one in the SH4 section back then, but it's all the same ofcourse)

The formula for the calculation is explained and proven in this document, around page 4.

http://www.filefront.com/17237360/NO...s_Only_TMA.pdf

It certainly seems to lend itself for a fixed bearing interval approach, but only with a digital calculator I fear. Making a sliderule for it would require another extra scale independant from the 2 that the fixed-time interval requires. The fixed bearing interval would require independant scales for both time periods, as wel as one for the size of the bearing interval (which I expect one would not like that to be built-in value). Or reducing the 2 'time' disks to one 'ratio of times'-disk wouldn't help in practice. You'd still have to do the division manually.

I haven't figured out how to construct such a thing. But after I finished working on the above slide-rule I definately thought about trying to implement it too. However the complexity of the formula got the better of me. Maybe it's time to pick up the attempt again. (it certainly beats wasting braincells on 8010)

[Rockin Robbins]

Originally Posted by Diopos

The minimum distance between a point A and a line is AB, B being the point where a Vertical -passing through A- cuts the line.


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Minor correction, not a vertical but a perpendicular.

[Diopos]

Originally Posted by Rockin Robbins

Minor correction, not a vertical but a perpendicular.

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[Rockin Robbins]

Originally Posted by Munchausen

Not always. Say the target cuts across your bow at about a 45 degree angle. It will be closest when on (or near) the bow and will be further away when AOB reaches 90.

The angles between the two courses don't matter. The point where a line drawn at right angles to the target course bisects your submarine is the closest approach. At that point the Angle on the Bow is 90º.

As I see it, Nisgeis has covered all the bases. The only problem is the reality that stopping a real submarine just can't happen unless you are on the surface. But that won't stop us from playing with the concept in the game.

[Nisgeis]

Originally Posted by Rockin Robbins

As I see it, Nisgeis has covered all the bases. The only problem is the reality that stopping a real submarine just can't happen unless you are on the surface. But that won't stop us from playing with the concept in the game.

It can be used with optical bearings as well when stationary. I don't think a minor creep speed to stay buoyant would affect the outcome too badly. You wouldn't get exactly the right course, but you'd get something in the right ball park.

[Munchausen]

Originally Posted by Rockin Robbins

The angles between the two courses don't matter. The point where a line drawn at right angles to the target course bisects your submarine is the closest approach. At that point the Angle on the Bow is 90º.

The concept should work ... but it's the observer or the sonar head or the radar ... not the submarine ... that's the center point. In fact, I tried for a long time to use sonar, thinking that the tangent would be when the sonar operator said, "constant distance" ... except he kept saying it ... on average, for about forty degrees of bearing.

[Rockin Robbins]

Originally Posted by Munchausen

The concept should work ... but it's the observer or the sonar head or the radar ... not the submarine ... that's the center point. In fact, I tried for a long time to use sonar, thinking that the tangent would be when the sonar operator said, "constant distance" ... except he kept saying it ... on average, for about forty degrees of bearing.

All measurements from your sub are standardized to be from a single point on the submarine, the center. So although sonar measurements are taken dozens of feet ahead of periscope measurements, the outputs are all normalized so that when the crew looks at a sonar bearing they can point the scope at that bearing and see the object. So radar, sonar, both periscopes all return the same bearings. This is true both in the game and on a real sub.

[Nisgeis]

Having another think about this. Once you have the target's course and you have obtained the speed by holding it at a contant bearing on a parallel course, you can find the range. You can work it out with some trig, using the right angled triangle between where the AoB was 90 and your earliest recorded time when the bearing was at a five degree interval. Using the distance travelled at that speed in that time elapsed with the formula Opposite = Adjacent * Tan(Angle) to fine the distance to track. Or you can simply draw out the distance travelled and find where that distance fits in the triangle and that will give you the range.

Assuming that you can speed match of course, but if you can't, then you will have trouble intercepting the faster target.

It's getting slightly more complicated now though. .

[Munchausen]

Why do you need the range if you already have track and speed?

[Nisgeis]

You have course and speed, but have no idea where the intercept point is unless you have range, so you'd have to approach purely on a constant bearing to guarantee an intercept, which is less than optimal.