Contact Intercept

[sixcoins]

Hello Sailors.

I'm having a problem with intercepting contacts. Spending a lot of time studying and trying it out, but I keep coming up short.

First, let me say I've done my studying. I'm reading the tutorials and practicing in game.

Right now, in particular, I'm using this tutorial. It seems to be all that I need for now, and this is the one I want to master. I'll add more tools to my bag later for certain, but right now my question is based on this method.

I'm using thread The Hunt: An illustrated example of how to sink a ship (http://www.subsim.com/radioroom/showthread.php?t=88961).

My problem comes up when it's time to draw the circle. Just for the sake of conversation, I'm using a scale factor of 10. If My target is going 9 knots, then my line showing his track is 90knots. Therefore, if my speed is 12, my compass circle is using a radius of 120.

The instructions i'm following for this part of the procedure is as follows...

So you draw a circle, centered at the end of the ruler measurement you did in step 3, with a radius of 160 mks... why 160 mks? because in step three you chose to represent each knot by 10 mks, remember? (If in step three you'de had measured 6 kms for the 6 knots you would now be drawing a circle radius of 16 kms for 16 knots, and so on). Let's look at your circle
http://static.flickr.com/36/93898889_aa6ce333c7_o.jpg
Take special notice of were the circle cuts the line formed from your u-boat to the contact.

This is where my problem comes in .... My circle never intersects the line formed from my u-boat to the contact. My circle is always waaaaay too big. It's the correct size according to the tutorial, which I understand it should be u-boat speed x 10. (10 is the multiplier I used when drawing the target ships course) However, even though it seems to be the correct numbers, it doesn't create any useful information. It's just a circle around the whole shebang.

I really want to be able to do this method. I won't be able to do it until I understand whatever it is that I'm overlooking.

Can anyone see my error? I can't.

Thanks in advance.

Six

[Pisces]

Maybe that's because there isn't one. You're not doing anything wrong I think so far. The circle intersects the line between you and the contact in the vicinity of the gridnumber AM24. Give me a moment while I upload my modified image.

The colors are in reference to Kylania's image I showed in another thread.

The light green protractor leg pointing ahead of the contact is the way to go.

http://img11.imageshack.us/img11/3036/interceptsixcoins.png

Link to Kylania's image: http://www.kylania.com/sh3/Intercept_Plotting.png

[sixcoins]

Thanks again Pisces.

I'll keep practicing it. I'm not sure why my circle keeps being bigger than my entire plot... Maybe I should be extending lines out further...

In my picture, it's all in one area inside one sector... In your picture, and in her picture, its over an area of about 4 sectors.

I guess I need to scale down a bit with the plotting tools, or use more of the map and draw longer lines....

Maybe that's why I'm having a hard time. Perhaps my common sense hasn't quite kicked in yet.

I'll keep trying, and thanks for all your help.

[Pisces]

Hmm, now I noticed this image was taken directly from the Hunt thread. :/\\!! Why don't you make a screen dump of your own map, and upload that? Then we can see what you are doing wrong. Instead of how Dantenoc did it.

[sixcoins]

Ok.... I have an example for you, Pisces. I wanted to show you what messes I'm making over here.

Here is a picture of MY plot.....

http://desmond.imageshack.us/Himg84/scaled.php?server=84&filename=sh3img3182012103435198.png&res=landing

Clearly I'm not paying attention to something that's important, but I just don't know what it is.

Clearly my circle is too big, but it does follow the instructions of the tutorial.

I'm thinking that there's some bonehead common sense procedure that every captain worth his weight in salt already knows. Except me.

Small Edit..... I DID scale my circle down until it cut through the line between myself and the contact... and when that happened, the circle ended up cutting through that line in 2 locations. And the distance of the circle was not any factor of 12. So.... that confused me even more.

Thanks again, in advance, for any help you can provide.


Six.

[complutum]

I think that your problem is your making circle radious with own speed by factor instead of use this value for circle diameter. in your example with own speed 12 knots he circle radious must be 60km that means 120km diameter.

[sixcoins]

I think that your problem is your making circle radious with own speed by factor instead of use this value for circle diameter. in your example with own speed 12 knots he circle radious must be 60km that means 120km diameter.

Possibly, but In the tutorial photo, they did use a factor of 10 for 16 knots, and the radius was 160Km. (and in that example, the target line was also 60 kilometers).

Tricky.

[MLGathome]

Hi, you made the correct drawing. But in this case your speed turns out to be to big. If you draw a circle of 60 (6 kts) or 90 (9kts) you wil see is intersects. After that you know your angle and still can steam up with 12 kts but you will arrive very early. It is all about math. If you understand it ones it is a peace of cake.

In this case you could draw a cirkel from position 60 towards your sub position, divide by 10 and you have your intersection speed. Intersection point would be position 60. Of course make sure your speed is a little higher because maybe your target is running 7 kts.

If the circle intercepts in two places, use the point closest to your sub to determine your angle.

In another ocassion, if your cirkel from 120 (12kts) would fit inside this triangle, and 12kts was your max speed, You should forget about intercepting this target.

Greetings, Marcel

[sublynx]

In other words use a smaller scale factor here. With x10 the circle gets too big, x5 might just be enough, but x3 would surely be ok.

Here's some pics, that hopefully clarify, unfortunately drawn in Google Sketchup as I don't have access to the game right now

http://i.imgur.com/IIqyw.jpg

http://i.imgur.com/YxHsK.jpg

http://i.imgur.com/Ee79N.jpg

http://i.imgur.com/SA4kK.jpg

[Captain Nemo]

I find the easiest and fastest way to intercept a contacts course is by doing the following:

1. Draw a line from the contact in the direction that it is heading.
2. Ask the navigator to plot a waypoint that intersects somewhere along the line (track) that you have drawn showing the contacts course.
3. See how long it will take your u-boat to reach that waypoint (intersection) and from this work out how far the contact would have travelled in this time. From this ajust your course (waypoint) accordingly.

Example: Contact is travelling east at 6 knots. At full speed my u-boat will take 2 hours to reach the contacts track. In this time the contact will have travelled just over 22 kilometres. From this decide if you need to move your waypoint along the contacts track closer to the original contacts position or further away to make the intercept.

Hope all that makes sense.

Nemo

[Mowgli]

I love these threads with all the charts and must try out these new skills one day but for now I am happy using the same method as Captain Nemo.

I also make use of the knots to kilometres travelled in n hours charts that are in the GWX super mod.

I like to arrive early and then man the hydrophone and listen for the thump thump of my approaching prey.

[MLGathome]

Everything Sublynx explained in hit maps is true and explaine well. You only should consider, do I won't to intercept during daylight? I noticed it is 10:02. If you arrive early and don't get your periscope up too many times, use torps from a short distance, it may work.

Good luck with your hunt, Marcel

[Pisces]

Ok.... I have an example for you, Pisces. I wanted to show you what messes I'm making over here.

Here is a picture of MY plot.....

http://desmond.imageshack.us/Himg84/scaled.php?server=84&filename=sh3img3182012103435198.png&res=landing

Clearly I'm not paying attention to something that's important, but I just don't know what it is.

Clearly my circle is too big, but it does follow the instructions of the tutorial.

I'm thinking that there's some bonehead common sense procedure that every captain worth his weight in salt already knows. Except me.

Small Edit..... I DID scale my circle down until it cut through the line between myself and the contact... and when that happened, the circle ended up cutting through that line in 2 locations. And the distance of the circle was not any factor of 12. So.... that confused me even more.

Thanks again, in advance, for any help you can provide.


Six.Yes, I see what you are missing. Due to your multiplication by 10 the red circle encompasses the entire distance from you to the target. The easy solution would be not to enlarge by 10, but just draw 1 for 1. (like Sublynx did in the later message with multiple images: #9, but that was apparently 3 for 1 )

Alternatively, if you didn't want to redraw the whole thing. The propper course of action (no pun) would be to extend the line between the target and you beyond your actual location. This is allowed because the line between you and the contact is supposed to be a bearingline extending into infinity. It shouldn't really stop where you are. The length of it is of no concern for the intercept course. Just as long as that green protractor angle has the corner at where you are.

You are forgiven, for it wasn't really explained in the Hunt thread. See the following image:

http://img515.imageshack.us/img515/9143/interceptsixcoins2.png

[Pisces]

I think that your problem is your making circle radious with own speed by factor instead of use this value for circle diameter. in your example with own speed 12 knots he circle radious must be 60km that means 120km diameter.No no, definitely not diameter. The edge of the circle represents the collection of courses at the defined own speed. It has to be the radius that must correspond to the speed. The target speed being 12 or 120, while the contact speed is (assumed) 6 or 60, thus halve of it, is entirely coincidence.

[sublynx]

Alternatively, if you didn't want to redraw the whole thing. The propper course of action (no pun) would be to extend the line between the target and you beyond your actual location. This is allowed because the line between you and the contact is supposed to be a bearingline extending into infinity. It shouldn't really stop where you are. The length of it is of no concern for the intercept course. Just as long as that green protractor angle has the corner at where you are.


Wow I didn't think about that solution to the problem at all. Very clever, and makes sense now that you point out the fact to us :)

[Pisces]

I find the easiest and fastest way to intercept a contacts course is by doing the following:

1. Draw a line from the contact in the direction that it is heading.
2. Ask the navigator to plot a waypoint that intersects somewhere along the line (track) that you have drawn showing the contacts course.
3. See how long it will take your u-boat to reach that waypoint (intersection) and from this work out how far the contact would have travelled in this time. From this ajust your course (waypoint) accordingly.

Example: Contact is travelling east at 6 knots. At full speed my u-boat will take 2 hours to reach the contacts track. In this time the contact will have travelled just over 22 kilometres. From this decide if you need to move your waypoint along the contacts track closer to the original contacts position or further away to make the intercept.

Hope all that makes sense.

NemoOk, lets say the initial AOB is 90 degrees port. (target goes from your right to left. And your fastest speed is 16 kts. ( so the initial distance to the track is 59 km in 2 hours)

After 2 hours the contact moved 22 kilometers along it's track.
This makes your distance to the new projected meeting point 63 km. (it's 22 degrees to the left)
But this will take longer: 2 hours 8 minutes.
And so, in that time the target moves 23.7 km.
This again moves the projected meeting point even further to the left (23.6 degrees)
And so your distance to this new meeting point grows slightly to 63.6 km
It would take you now a minute more to reach that.
And so on,
and so on. But let's consider this minute close enough for now

In other situations you might have to do more repeated calculations, as your distance to the projected meeting point creeps further away.

So, how do you consider repeatedly calculating the distance that the target moves in the same time it takes you to do it "the easiest and fastest"?

To each his own method, of course. But I think those words better apply to the graphical method as described. Where no calculation is needed.

[sixcoins]

Thanks so very much, to all of you. This definitely clears it all up for me... And now I can practice instead of pulling my hair out of my head.

Six.

[Pisces]

...
Small Edit..... I DID scale my circle down until it cut through the line between myself and the contact... and when that happened, the circle ended up cutting through that line in 2 locations. ... 2 intersections is indeed possible if your chosen intercept speed is close to the minimum required. The minimum speed is when the red circle touches the (infinite) black bearing line between you and the target. Another way to draw it is to drag the corner of the yellow protractor along the black line until it is 90 degrees. You have to go faster than that, or you will never meet!

The closer intersection of the red circle and the black line is the slower way to close. The course that results is actually having you trying to get away from him along the bearing line. But his closing outways your moving away. Always use the furthest intersection.

...
And the distance of the circle was not any factor of 12. So.... that confused me even more.That's why I suggest not to multiply with odd-lot numbers, 2,3,4,5,6,7... . Stick to 1, or 10. And extend that bearing line if needed. No brain-burning by multiplying is required.

[Maceaciadh]

Ok, lets say the initial AOB is 90 degrees port. (target goes from your right to left. And your fastest speed is 16 kts. ( so the initial distance to the track is 59 km in 2 hours)

After 2 hours the contact moved 22 kilometers along it's track.
This makes your distance to the new projected meeting point 63 km. (it's 22 degrees to the left)
But this will take longer: 2 hours 8 minutes.
And so, in that time the target moves 23.7 km.
This again moves the projected meeting point even further to the left (23.6 degrees)
And so your distance to this new meeting point grows slightly to 63.6 km
It would take you now a minute more to reach that.
And so on,
and so on. But let's consider this minute close enough for now

In other situations you might have to do more repeated calculations, as your distance to the projected meeting point creeps further away.

So, how do you consider repeatedly calculating the distance that the target moves in the same time it takes you to do it "the easiest and fastest"?

To each his own method, of course. But I think those words better apply to the graphical method as described. Where no calculation is needed.

this is by far the easiest and fastest method out there(i use it). perhaps you have misunderstood what he meant by it. you draw a line of the contacts course and if you want mark crosses every 16KM(ship at 8Kts) to help visualise it(just double the speed in knots gives you a slight overestimation in KMpH) then as stated set course to an appropriate point on that line. you move your waypoint along the line and the navigator gives you a time to that waypoint. adjust accordingly and you are there. no fuss, no hassle, no time wasted drawing stuff (unless you like that way). after all the targets heading is an estimation so why solve it properly something that is wrong?

a bit hard to explain without pictures but really there are 2 bits of math
1)doubling ships speed from Kt to KMpH
2)roughly guessing where your intercept is.

FYI after the target travels 102KM it has a possibility of being beyond hydrophone range from the bearing inaccuracy (20KM radius)

after a while you develop a seamans eye and can drag it almost perfectly to an intercept

PS if in heavy fog may be better to do that whole circle business to save diving and listening alot but you can still be wrong over long distances so be careful

[Pisces]

this is by far the easiest and fastest method out there(i use it). perhaps you have misunderstood what he meant by it. you draw a line of the contacts course and if you want mark crosses every 16KM(ship at 8Kts) to help visualise it(just double the speed in knots gives you a slight overestimation in KMpH) then as stated set course to an appropriate point on that line. you move your waypoint along the line and the navigator gives you a time to that waypoint. adjust accordingly and you are there. no fuss, no hassle, no time wasted drawing stuff (unless you like that way).Ok, so this method is more guestimating than calculating. But still, it requires multiple checks (at hour marks) to see if you got there already.

after all the targets heading is an estimation so why solve it properly something that is wrong?

a bit hard to explain without pictures but really there are 2 bits of math
1)doubling ships speed from Kt to KMpH
2)roughly guessing where your intercept is.

...
Because you want to get as close as possibl. Especially with fog and long range. Adding causes for error deliberately (like overestimating that 16 km equals 8 nautical mile) doesn't help with that. You want to be as exact as possible. Sure, the target course is uncertain. But that applies to both methods. Yours won't handle it any better than mine.


FYI after the target travels 102KM it has a possibility of being beyond hydrophone range from the bearing inaccuracy (20KM radius)Then it's a good thing that the hydrophone actually works upto 33km. It's the crew that is either too deaf, or to lazy to report what you can hear yourself. So you have until 170 km.


after a while you develop a seamans eye and can drag it almost perfectly to an interceptOk, that is true. Trial and error makes those braincells learn to do it intuitively. But you'll also get the hang of making that drawing after a while. You'll do it blindfolded. Ok, not litterally. :)


PS if in heavy fog may be better to do that whole circle business to save diving and listening alot but you can still be wrong over long distances so be carefulYes, it all boils down to how sure you can be of the target speed and course. But also how well you can keep your own speed (and course). You always have to consider the possibilities that it's going to fail. That's why I try to reduce as much causes.

[Maceaciadh]

what hour checks are you on about? it takes me 20 seconds to set course to the intercept. i miss maybe 4 out of 5 times which is probably just changing of course.

also yea i read that on another thread (guessing you read it) i am going to start listening myself soon

[Pisces]

To add:

There is a fairly simple addition to the method to end up at a certain minimal distance away from the contact at the meeting point. You won't be able to figure out that easily with that alternate method.

But it would be considered more advanced. So if Sixcoins doesn't want to get overwhelmed he should cover his eyes now:

[Edit] This does require fairly reliable speed and course of the target. Most likely use is after first contact, and dodging around units in the dark.

1: You would replace the point of the contact location with a circle of minimum safe distance.

2: Then you would choose, "do I want to pass behind or in front of him?". In the image below you want to pass ahead of him.

3: draw the bearing line from the contact towards you along the edge of the minimum distance circle. Then continue from that.

http://img228.imageshack.us/img228/4711/minimumdistanceintercep.png

[Maceaciadh]

still confused why you are putting some things forward there but if you like to draw stuff with your time who am i to argue lmao surely once you get within visual range you delete your first line and start taking more accurate visual measures or indeed hydrophone ones to find out speed and bearing.

also forgot to say on the last post but the 7% over error by just doubling makes for a good early arrival time. if you want to trail them like a convoy then just wait while they pass and take notes of all the good high tonnage ships within it. arriving early is always good even if you want to shadow.

[Pisces]

still confused why you are putting some things forward there but if you like to draw stuff with your time who am i to argue lmao surely once you get within visual range you delete your first line and start taking more accurate visual measures or indeed hydrophone ones to find out speed and bearing.Safety precautions. I want to set a course that gets me closer, but not too close. The dashed line is just shown to see how it compares with the 'straight' intercept way. It is not used.

also forgot to say on the last post but the 7% over error by just doubling makes for a good early arrival time. if you want to trail them like a convoy then just wait while they pass and take notes of all the good high tonnage ships within it. arriving early is always good even if you want to shadow.That works too. But with your way your 'early time' is directly proportional to the distance at the start, or how long the intercept took. So for long distance targets you will arrive more early than closer ones. I don't see the need for that. With this added circle to the method you should pass it a fixed stand-off distance every time.

[CaliEs]

Link to Kylania's image: http://www.kylania.com/sh3/Intercept_Plotting.png This drawing make only sense when the blue line is measured as 16.0, not 6 as indicated.

[Pisces]

This drawing make only sense when the blue line is measured as 16.0, not 6 as indicated.I admit that it doesn't look properly to scale. But the steps are geometrically correct.

[TorpX]

I haven't used this method, so I decided to break out a pencil and paper and take a closer look at it. For some reason my brain learns better from graphite on paper, than illuminated pixels on a computer screen. :)


I must admit I like this method, now that I understand it. However, there is a simpler alternative that will suffice in many cases. This is the Normal Approach Course. I'm guessing some here already know what this is, but I thought I'd outline it for those who don't.


The Normal Approach Course gets it's name from the fact that you are taking a course normal (perpendicular) to the target. That is, if the target is on a closing track, the true bearing of the target is 25 deg., and it is drawing off to the South, you would steer 115 deg. true. You don't need to know the distance, exact course, or speed of the target. (This makes it ideal in situations where you have only a sound contact.) By the way the situation develops, you will know if a interception is possible:

Case 1- You are gaining bearing on the target.
That is the true bearing of the target goes from 25 to 24 to 23 deg., etc., etc. You can maintain your speed and reach the target's track ahead of it. You can reduce speed to intercept. Or, you can maintain speed and cut into the target's track to intercept sooner.

Case 2- True bearing of the target is constant.
If you and the target hold course and speed, an interception is assured. (You are on a collision course!)

Case 3- You are losing bearing on the target. That is, the target's bearing is going from 25 to 26 to 27 deg., etc. In this case an interception at this speed is impossible. You must either increase speed, or consider weather it is advisable to continue the approach (it is sometimes possible to get close enough for a torpedo attack even though an "interception" does not take place).

The key element of the Normal Approach Course is that it allows an intercept at a minimum of speed. Another critical element is that it is only relevant for targets on a closing track (moving closer to you). Following a Normal Approach Course on a target that is already moving away from you will avail you nothing. In this case you would be better off to follow the method already explained in this thread.

[Pisces]

I haven't used this method, so I decided to break out a pencil and paper and take a closer look at it. For some reason my brain learns better from graphite on paper, than illuminated pixels on a computer screen. :)


I must admit I like this method, now that I understand it. However, there is a simpler alternative that will suffice in many cases. This is the Normal Approach Course. I'm guessing some here already know what this is, but I thought I'd outline it for those who don't.

...
This is definitely the best solution if you are submerged, and slow. It does make the intercept take quite a while though. You'll make the target do all the closing of the gap. So turning into the target whenever his bearing is changing towards your rear is very advisable to reduce the time. If all you have is a bearing, then this is the simplest way to go. With a periscope view the bearing change is even more easier to see.

[Captain Nemo]

Ok, lets say the initial AOB is 90 degrees port. (target goes from your right to left. And your fastest speed is 16 kts. ( so the initial distance to the track is 59 km in 2 hours)

After 2 hours the contact moved 22 kilometers along it's track.
This makes your distance to the new projected meeting point 63 km. (it's 22 degrees to the left)
But this will take longer: 2 hours 8 minutes.
And so, in that time the target moves 23.7 km.
This again moves the projected meeting point even further to the left (23.6 degrees)
And so your distance to this new meeting point grows slightly to 63.6 km
It would take you now a minute more to reach that.
And so on,
and so on. But let's consider this minute close enough for now

In other situations you might have to do more repeated calculations, as your distance to the projected meeting point creeps further away.

So, how do you consider repeatedly calculating the distance that the target moves in the same time it takes you to do it "the easiest and fastest"?

To each his own method, of course. But I think those words better apply to the graphical method as described. Where no calculation is needed.

I can see where your coming from in theory but in practice it doesn't work that way. I might make one adjustment to the waypoint that intersects the contacts course once I know how long its going to take me to get there and how far the contact would have travelled in that time (I use a pre-printed table for this), but other than that that's it. I always set the waypoint so I'll get there just before the contact does, about 5-10 Kms. I would say that unless the contact makes a course change between the contact report and the point of intercept it will work 99.9% of the time.

Nemo