Intercept course?

Kip336 · 03-06-13, 12:37 PM

Yesterday I had a really good generated ASUW game in a 688i. Instead of directly pounding the enemy vessel like I usually do, I decided to do things the other way, and just track the vessel for a while.

As he was off on my bow, I wanted to get a nice intercept course. Other then guessing though, I didn't have any means to calculate the proper course.
Does anyone know how to calculate a intercept course? In SH3 you atleast had some good drawing tools to use to calculate it, but not in DW..

I ended up going onto a lagging course, slipping in behind him and then caught up to him by going just a knot or two faster.(He had no TA...)

(Also, even though you're just YARDS behind a big surface ship, you dont hear the ship outside of the sonar station

)

Beardmoresam · 03-06-13, 12:41 PM

I think you need to do a relative motion-plot-thing, although I'm no expert.
Basically I mark up my speed and heading + his speed and heading and see where it leaves us in x amount of time. I can then speed up or change course to make it more suited to my needs.

Pisces · 03-06-13, 04:07 PM

[EDITED for simplicty]
I take the TARGET COURSE.
I subtract the TARGET BEARING from it. (don't care if the result is negative or beyond 360)
I take the sine function of it with a scientific calculator. (make sure it is in degree mode, not radians or gradians)
I multiply the result by the target speed.
I divide by my chosen intercept speed.

If the result is less than -1, or bigger than 1, then forget about chasing it, or speed up and redo the calculation. Bigger than 1 (or less than -1) means he's outrunning you. Exactly (-) 1 means the best you can do is move perpendicular to the bearing, and let him close the distance to you.

Take the inv(erse) sin, or arcsin, or asin, or sin -1 (!superscript) of the result.

[EDITED] Add the arcsin result to the TARGET BEARING. If the asin result is negative, then adding a negative is the same as subtracting from the TARGET BEARING while ignoring the sign.

Head that way, unless it keeps him in your sonar deaf-zones. Then you have to turn a bit to keep an ear on him, and make do with a bit less efficient intercept.

Pisces · 03-06-13, 05:09 PM

In (Casio fx-82SX) button code:

Press mode button
Press 4
(Casio fx-82SX enters degrees mode)
Press AC a couple of time to clear accumulator memory.

Enter Target Course,
Press - (subtract)
Enter Target Bearing,
Press =,
Press Sin,
Press x (Multiply),
Enter Target Speed,
Press ./. (Divide)
Enter Ownship Speed
Press =,
Observe if between -1 and 1. If not, speed up and redo calculations.

Press Shift button,
Press Sin (Sin after Shift= arcsin)
Press +
Enter Target Bearing,
Press =

Set course to that!

If he is moving away then you obviously need to be faster than him.

CapitanPiluso · 03-06-13, 05:12 PM

For a complete intercept solution you could try Mobo http://www.subsim.com/radioroom/showthread.php?t=118990

Zander · 03-06-13, 06:14 PM

Quote:

Originally Posted by Kip336

Yesterday I had a really good generated ASUW game in a 688i. Instead of directly pounding the enemy vessel like I usually do, I decided to do things the other way, and just track the vessel for a while.

As he was off on my bow, I wanted to get a nice intercept course. Other then guessing though, I didn't have any means to calculate the proper course.
Does anyone know how to calculate a intercept course? In SH3 you atleast had some good drawing tools to use to calculate it, but not in DW..

)

Are you saying that TMA doesn't give you a course, allowing you to plot an intercept point further out? TMA does give you course among other things, like speed, range....
Take a look at this you tube tutorial video, and note that at about 1:36min mark, he has speed, bearing, range and course down to a 1150 yards of the actual position along with its course..
I trust your question was in relation to tracking a target such that you can derive its course? If so the sonar and TMA does everything that you need to acomplish that. Here is the you tube link :

Look at his solution at about 1:33...

With speed and course you can easily calculate a possible intercept position, from his "present" position using the nav map tools.

Beardmoresam · 03-07-13, 01:54 PM

Pisces, i'm not great at math but I'm guessing range cancels out in your equation by the fact that the further you are from target, the further you both have to travel to intercept??

I'm used to plotting it by vector analysis on paper as I hate trig lol.

Pisces · 03-07-13, 02:19 PM

Quote:

Originally Posted by Beardmoresam

Pisces, i'm not great at math but I'm guessing range cancels out in your equation by the fact that the further you are from target, the further you both have to travel to intercept??

I'm used to plotting it by vector analysis on paper as I hate trig lol.

Correct.

A picture makes more sense than a thousand words, so I agree with the paper method. But it does take some time, and clutter on the desk.

Kip336 · 03-08-13, 04:39 AM

I'll actually use the calculator option ... I tend to keep my iPhone close so I'm sure itll work.

Kip336 · 03-08-13, 12:25 PM

Arright.
I did some testing on my iPhone at work, and it seems to give out a pretty ok calculation. However, when I was doing it on a paper plot, target range was part of the plot. How is that not important in this calculation? For small distances, it barely matters. But when Im trying to get in a position to engage a russian fleet steaming at 20 knots, 50nm away, the distance between us should matter no?

Beardmoresam · 03-09-13, 01:45 PM

With the method that Pisces described, nope. There are some very good visual animations for describing the effect on the SH4 forum. Just look up the Dick O'Kane method.

Pisces · 03-09-13, 03:45 PM

It's all about the angles inside a triangle. The speeds arranged into a triangle must be of the same shape as the triangle made up of target course, intercept course and target bearing. The size of the triangle, or the exact lengths of the sides in terms of real distance doesn't matter for getting there at the same time as he does. Because the time it takes is the same for all lengths of the triangle sides, it can be taken out of the equation. You reduce the problem into an 1 hour situation.

From that you can calculate the missing pieces of information inside the triangle. You have to make use of a math rule known as the law of sines: the ratio of side length to the sine of opposing angle, is the same for all side/corner combinations.

a/sin(alpha)=b/sin(beta)=c/sin(gamma)

If alpha is AOB (the corner occupied by the target), then a is own speed.
If b is target speed, then beta is lead-angle (deflection; the corner occupied by you)
C would then be the closing speed along the target bearing.
And gamma would be the angle of the intercept point corner. (track angle???)

You only have to know 3 (AOB, own speed, targetspeed) out of 4 to calculate the missing lead-angle b.

The angle of the intercept point corner/ trackangle is not really of interest in practical use, but it is required if you want to calculate the time it takes to get to the intercept point. Since the closing speed determines the time needed for the range to be reduced to zero. So, since the sum of all angles inside a triangle is 180, you can figure out the gamma angle. Plugging that into the: a/sin(alpha)=c/sin(gamma) equation you can now calculate c (closing speed). And ultimately the time it takes to the intercept point from range.

jadervason · 11-01-16, 06:17 PM

Necropost, I know...

but my "Dirty" method of intercept is simple: start by matching course with the target. turn (toward the bearing rate) so that bearing rate of the target is reduced to zero. apart from certain exceptions, you are now on an intercept course

With practice you will be able to make educated guesses as to how much to turn with trial and error. I usually do it in 10 degree chunks but you can just set the rudder and ease back when you get close also

rentacow · 11-03-16, 03:34 AM

I use this: http://www.luizmonteiro.com/RA.aspx

Very handy tools on that website!

p7p8 · 11-03-16, 12:12 PM

Intercept course in DW is not really needed for playing.

1) your sensors have different "dead zones" so you can't track your target like in SH. more important is maneuvering for good TMA solutions

2) almost all subs can go very fast underwater so math methods for interception target moving with 10 knots when you can drive with 20-35 knots is pointless

3) your weapons can do this automaticly

4) your weapon can be wire-guided

5) your weapon have own radar,sonar active/passive, IR detector etc.

6) going straight for long time with constant speed is not too good for you, because you are easy target for opponents

My advise:
Don't play DW like SH.

03-06-13, 12:37 PM	#1
Kip336 Torpedoman Join Date: Jun 2009 Posts: 119 Downloads: 19 Uploads: 0	Intercept course? Yesterday I had a really good generated ASUW game in a 688i. Instead of directly pounding the enemy vessel like I usually do, I decided to do things the other way, and just track the vessel for a while. As he was off on my bow, I wanted to get a nice intercept course. Other then guessing though, I didn't have any means to calculate the proper course. Does anyone know how to calculate a intercept course? In SH3 you atleast had some good drawing tools to use to calculate it, but not in DW.. I ended up going onto a lagging course, slipping in behind him and then caught up to him by going just a knot or two faster.(He had no TA...) (Also, even though you're just YARDS behind a big surface ship, you dont hear the ship outside of the sonar station )

03-06-13, 04:07 PM	#3
Pisces Silent Hunter Join Date: Dec 2004 Location: AN9771 Posts: 4,893 Downloads: 304 Uploads: 0	[EDITED for simplicty] I take the TARGET COURSE. I subtract the TARGET BEARING from it. (don't care if the result is negative or beyond 360) I take the sine function of it with a scientific calculator. (make sure it is in degree mode, not radians or gradians) I multiply the result by the target speed. I divide by my chosen intercept speed. If the result is less than -1, or bigger than 1, then forget about chasing it, or speed up and redo the calculation. Bigger than 1 (or less than -1) means he's outrunning you. Exactly (-) 1 means the best you can do is move perpendicular to the bearing, and let him close the distance to you. Take the inv(erse) sin, or arcsin, or asin, or sin -1 (!superscript) of the result. [EDITED] Add the arcsin result to the TARGET BEARING. If the asin result is negative, then adding a negative is the same as subtracting from the TARGET BEARING while ignoring the sign. Head that way, unless it keeps him in your sonar deaf-zones. Then you have to turn a bit to keep an ear on him, and make do with a bit less efficient intercept. Last edited by Pisces; 03-06-13 at 04:56 PM. Reason: Make it simpler

03-06-13, 05:12 PM	#5
CapitanPiluso Forum Captain Join Date: Apr 2007 Location: Buenos Aires Posts: 273 Downloads: 22 Uploads: 0	For a complete intercept solution you could try Mobo http://www.subsim.com/radioroom/showthread.php?t=118990 __________________ (Yo no fui ) My DW pics :https://goo.gl/photos/5gBN7WFntLBSAsc17 My SSM2007 pics :https://goo.gl/photos/1Fa6GaEom28AZuc57

11-03-16, 03:34 AM	#14
rentacow Machinist's Mate Join Date: Sep 2014 Location: Onakushcloud Posts: 126 Downloads: 58 Uploads: 0	I use this: http://www.luizmonteiro.com/RA.aspx Very handy tools on that website! __________________ Dangerous Waters scenarios on pastebin.

03-06-13, 12:41 PM	#2
Beardmoresam A-ganger Join Date: Oct 2011 Posts: 74 Downloads: 434 Uploads: 0	I think you need to do a relative motion-plot-thing, although I'm no expert. Basically I mark up my speed and heading + his speed and heading and see where it leaves us in x amount of time. I can then speed up or change course to make it more suited to my needs.

03-06-13, 05:09 PM	#4
Pisces Silent Hunter Join Date: Dec 2004 Location: AN9771 Posts: 4,893 Downloads: 304 Uploads: 0	In (Casio fx-82SX) button code: Press mode button Press 4 (Casio fx-82SX enters degrees mode) Press AC a couple of time to clear accumulator memory. Enter Target Course, Press - (subtract) Enter Target Bearing, Press =, Press Sin, Press x (Multiply), Enter Target Speed, Press ./. (Divide) Enter Ownship Speed Press =, Observe if between -1 and 1. If not, speed up and redo calculations. Press Shift button, Press Sin (Sin after Shift= arcsin) Press + Enter Target Bearing, Press = Set course to that! If he is moving away then you obviously need to be faster than him.

03-07-13, 01:54 PM	#7
Beardmoresam A-ganger Join Date: Oct 2011 Posts: 74 Downloads: 434 Uploads: 0	Pisces, i'm not great at math but I'm guessing range cancels out in your equation by the fact that the further you are from target, the further you both have to travel to intercept?? I'm used to plotting it by vector analysis on paper as I hate trig lol.

03-08-13, 04:39 AM	#9
Kip336 Torpedoman Join Date: Jun 2009 Posts: 119 Downloads: 19 Uploads: 0	I'll actually use the calculator option ... I tend to keep my iPhone close so I'm sure itll work.

03-08-13, 12:25 PM	#10
Kip336 Torpedoman Join Date: Jun 2009 Posts: 119 Downloads: 19 Uploads: 0	Arright. I did some testing on my iPhone at work, and it seems to give out a pretty ok calculation. However, when I was doing it on a paper plot, target range was part of the plot. How is that not important in this calculation? For small distances, it barely matters. But when Im trying to get in a position to engage a russian fleet steaming at 20 knots, 50nm away, the distance between us should matter no?

03-09-13, 01:45 PM	#11
Beardmoresam A-ganger Join Date: Oct 2011 Posts: 74 Downloads: 434 Uploads: 0	With the method that Pisces described, nope. There are some very good visual animations for describing the effect on the SH4 forum. Just look up the Dick O'Kane method.

03-09-13, 03:45 PM	#12
Pisces Silent Hunter Join Date: Dec 2004 Location: AN9771 Posts: 4,893 Downloads: 304 Uploads: 0	It's all about the angles inside a triangle. The speeds arranged into a triangle must be of the same shape as the triangle made up of target course, intercept course and target bearing. The size of the triangle, or the exact lengths of the sides in terms of real distance doesn't matter for getting there at the same time as he does. Because the time it takes is the same for all lengths of the triangle sides, it can be taken out of the equation. You reduce the problem into an 1 hour situation. From that you can calculate the missing pieces of information inside the triangle. You have to make use of a math rule known as the law of sines: the ratio of side length to the sine of opposing angle, is the same for all side/corner combinations. a/sin(alpha)=b/sin(beta)=c/sin(gamma) If alpha is AOB (the corner occupied by the target), then a is own speed. If b is target speed, then beta is lead-angle (deflection; the corner occupied by you) C would then be the closing speed along the target bearing. And gamma would be the angle of the intercept point corner. (track angle???) You only have to know 3 (AOB, own speed, targetspeed) out of 4 to calculate the missing lead-angle b. The angle of the intercept point corner/ trackangle is not really of interest in practical use, but it is required if you want to calculate the time it takes to get to the intercept point. Since the closing speed determines the time needed for the range to be reduced to zero. So, since the sum of all angles inside a triangle is 180, you can figure out the gamma angle. Plugging that into the: a/sin(alpha)=c/sin(gamma) equation you can now calculate c (closing speed). And ultimately the time it takes to the intercept point from range.

11-01-16, 06:17 PM	#13
jadervason Bosun Join Date: Aug 2009 Posts: 69 Downloads: 15 Uploads: 0	Necropost, I know... but my "Dirty" method of intercept is simple: start by matching course with the target. turn (toward the bearing rate) so that bearing rate of the target is reduced to zero. apart from certain exceptions, you are now on an intercept course With practice you will be able to make educated guesses as to how much to turn with trial and error. I usually do it in 10 degree chunks but you can just set the rudder and ease back when you get close also

11-03-16, 12:12 PM	#15
p7p8 Seasoned Skipper Join Date: Nov 2006 Posts: 742 Downloads: 136 Uploads: 6	Intercept course in DW is not really needed for playing. 1) your sensors have different "dead zones" so you can't track your target like in SH. more important is maneuvering for good TMA solutions 2) almost all subs can go very fast underwater so math methods for interception target moving with 10 knots when you can drive with 20-35 knots is pointless 3) your weapons can do this automaticly 4) your weapon can be wire-guided 5) your weapon have own radar,sonar active/passive, IR detector etc. 6) going straight for long time with constant speed is not too good for you, because you are easy target for opponents My advise: Don't play DW like SH.