Intercept Plotting - it works, sorta

vonCrandall · 05-07-09, 09:12 AM

I am using this post as my general intercept plotting forumla and for targets a few Kilometers out it has worked quite well the last day or so.

http://www.subsim.com/radioroom/show...2&postcount=41

However, I am running into a problem charting an intercept for very long range covoys that are reported, yet interceptable. I do everything the same, yet when I use the compass to input the speed values, since the distance is so far, it gives me maybe only a few degree adjustment. Do I need to modify something (i.e. make the speed values double every X distance, etc) if the covoy is severl hundred kilometers away, or does this work the same?

sharkbit · 05-07-09, 09:19 AM

I don't know if you were trying to post a link in your post or not, but are you using this technique to intercept targets:
http://www.subsim.com/radioroom/showthread.php?t=88961

And welcome aboard!

vonCrandall · 05-07-09, 09:22 AM

Sorry, forgot the link. It's there now.

My question is - what needs to be changed (if anything), if the intercept will take longer than an hour? I run into a problem when the convoy is VERY far away and obviously using the method linked, estimating 6 knots for them and my 12 knots is only good for an hour (I think).

Do i simply need to multiple the speeds verses the estimated time until an intercept?

sharkbit · 05-07-09, 09:35 AM

Read the link that I provided. It does a much better job at explaining the process and is usable for long distance intercepts. I think it is the best and simplest method for plotting intercepts. It expands greatly on the link you posted. Both are doing basically the same thing. I use it all the time and is second nature now.

To try and answer your question though: You basically multiply the target spped factor, but you have to multiply your speed for the intercept as well by the same factor.

Hope all this helps.

Pisces · 05-07-09, 10:31 AM

The method works perfect for ANY range. However, it only works if the course and speed of the contact is actually true. And likely it isn't! The course reported has a validity-fan of 11.25 degrees on either side (for example, if NE is reported it could really mean any course within 33.75 and 56.25). To easily plot these fan-edges is to draw a line of 175km along the stated course. Draw a 34km radius circle at the end. Draw 2 lines tangent to the circle. Why 34km at 175km? That distance is where the course edges start to fall outside of your hydrophone coverage. Any further and finding them is not guaranteed anymore if the course was near the edges. It is still possible finding it if it is on the inside though. But who knows that for sure?

If the actual speed of the contact is different from the reported speed (as it seems to be the rounded value, or it is stated as a speed-range) the intercept also looses chance of working. This means the intercept method in the link can only be an approximation.

Therefore very distant intercepts, based on these uncertainties are prone to fail. Especially considering it can ALSO change course in the mean time. My personal solution to this problem is to make the drawing based on worst cases, and the 175km 'contact maximum move' rule :

speed:
- upper-end of the speed-range for single units. (slow=7.5 knots, medium=11.5 knots)
- add 0.5 knots to the reported convoy speed

course:
- assume course is the 11.25 edge that has AOB nearest to 90 (at the start of the intercept).

Once you reach that edge of the course-fan and you can't hear anything (yourself) with the hydrophone you should attempt another intercept based on the other course edge. But with the expected position of that moment. Not the old location. So you need to plot where he would be now, based on how much time has passed since the icon appeared. NEVER forget to write down that time!

If you chased a single unit with a worst-case speed it may not yet be inside your hydrophone range when you are on the central-course. But you can safely assume you are ahead of him. It just requires patience to wait for him while being on the central course. Or you move to meet him along the central course (but ofcourse going in opposite direction) while doing frequent hydrophone checks.

And ofcourse, it all depends on how accurate you made the drawing in the first place. Perhaps the drawing is more accurate if you make the circles with a scale of 10 kilometers for each knot.

Pisces · 05-07-09, 11:22 AM

Quote:

Originally Posted by sharkbit

Read the link that I provided. It does a much better job at explaining the process and is usable for long distance intercepts.

Actually, they are both of the same thread, and same technique. But the image in the first link is a summerised version.

Pisces · 05-07-09, 11:37 AM

p.s. to add to my big rant above:

I move at an intercept speed on the surface as fast as possible. But not at flank, as it is like having a hole in your tank. So i set full speed @ 16.5 knots in a type-7. And don't worry about how long it takes ( 11 hours is possible). As long as the target doesn't move beyond 175km before you hear him, he's toast. A soggy one, but toast nonetheless.

But do check if you are not slowed down by wind and waves. Then you need to correct your earlier drawing.

sharkbit · 05-07-09, 12:06 PM

Quote:

Originally Posted by Pisces

Actually, they are both of the same thread, and same technique. But the image in the first link is a summerised version.

My bad.

Haven't gone thru that whole thread in a long time. I have a copy of the PDF file somewhere that I used to refer to.

05-07-09, 09:12 AM	#1
vonCrandall Mate Join Date: May 2009 Posts: 57 Downloads: 94 Uploads: 0	Intercept Plotting - it works, sorta I am using this post as my general intercept plotting forumla and for targets a few Kilometers out it has worked quite well the last day or so. http://www.subsim.com/radioroom/show...2&postcount=41 However, I am running into a problem charting an intercept for very long range covoys that are reported, yet interceptable. I do everything the same, yet when I use the compass to input the speed values, since the distance is so far, it gives me maybe only a few degree adjustment. Do I need to modify something (i.e. make the speed values double every X distance, etc) if the covoy is severl hundred kilometers away, or does this work the same?

05-07-09, 09:19 AM	#2
sharkbit The Old Man Join Date: Apr 2008 Location: Denver, CO Posts: 1,529 Downloads: 334 Uploads: 0	I don't know if you were trying to post a link in your post or not, but are you using this technique to intercept targets: http://www.subsim.com/radioroom/showthread.php?t=88961 And welcome aboard! __________________ “Prejudice is blind. There will always be someone who says you aren’t welcome at the table. Stop apologizing for who you are and using all your energy trying to change their minds. Yes, you will lose friends, maybe even family. But you will gain your self-respect. You will know your worth. Once you have that, nothing can stop you.”

05-07-09, 09:35 AM	#4
sharkbit The Old Man Join Date: Apr 2008 Location: Denver, CO Posts: 1,529 Downloads: 334 Uploads: 0	Read the link that I provided. It does a much better job at explaining the process and is usable for long distance intercepts. I think it is the best and simplest method for plotting intercepts. It expands greatly on the link you posted. Both are doing basically the same thing. I use it all the time and is second nature now. To try and answer your question though: You basically multiply the target spped factor, but you have to multiply your speed for the intercept as well by the same factor. Hope all this helps. __________________ “Prejudice is blind. There will always be someone who says you aren’t welcome at the table. Stop apologizing for who you are and using all your energy trying to change their minds. Yes, you will lose friends, maybe even family. But you will gain your self-respect. You will know your worth. Once you have that, nothing can stop you.”

05-07-09, 10:31 AM	#5
Pisces Silent Hunter Join Date: Dec 2004 Location: AN9771 Posts: 4,904 Downloads: 304 Uploads: 0	The method works perfect for ANY range. However, it only works if the course and speed of the contact is actually true. And likely it isn't! The course reported has a validity-fan of 11.25 degrees on either side (for example, if NE is reported it could really mean any course within 33.75 and 56.25). To easily plot these fan-edges is to draw a line of 175km along the stated course. Draw a 34km radius circle at the end. Draw 2 lines tangent to the circle. Why 34km at 175km? That distance is where the course edges start to fall outside of your hydrophone coverage. Any further and finding them is not guaranteed anymore if the course was near the edges. It is still possible finding it if it is on the inside though. But who knows that for sure? If the actual speed of the contact is different from the reported speed (as it seems to be the rounded value, or it is stated as a speed-range) the intercept also looses chance of working. This means the intercept method in the link can only be an approximation. Therefore very distant intercepts, based on these uncertainties are prone to fail. Especially considering it can ALSO change course in the mean time. My personal solution to this problem is to make the drawing based on worst cases, and the 175km 'contact maximum move' rule : speed: - upper-end of the speed-range for single units. (slow=7.5 knots, medium=11.5 knots) - add 0.5 knots to the reported convoy speed course: - assume course is the 11.25 edge that has AOB nearest to 90 (at the start of the intercept). Once you reach that edge of the course-fan and you can't hear anything (yourself) with the hydrophone you should attempt another intercept based on the other course edge. But with the expected position of that moment. Not the old location. So you need to plot where he would be now, based on how much time has passed since the icon appeared. NEVER forget to write down that time! If you chased a single unit with a worst-case speed it may not yet be inside your hydrophone range when you are on the central-course. But you can safely assume you are ahead of him. It just requires patience to wait for him while being on the central course. Or you move to meet him along the central course (but ofcourse going in opposite direction) while doing frequent hydrophone checks. And ofcourse, it all depends on how accurate you made the drawing in the first place. Perhaps the drawing is more accurate if you make the circles with a scale of 10 kilometers for each knot. __________________ My site downloads: https://ricojansen.nl/downloads Last edited by Pisces; 05-07-09 at 11:30 AM.

05-07-09, 11:37 AM	#7
Pisces Silent Hunter Join Date: Dec 2004 Location: AN9771 Posts: 4,904 Downloads: 304 Uploads: 0	p.s. to add to my big rant above: I move at an intercept speed on the surface as fast as possible. But not at flank, as it is like having a hole in your tank. So i set full speed @ 16.5 knots in a type-7. And don't worry about how long it takes ( 11 hours is possible). As long as the target doesn't move beyond 175km before you hear him, he's toast. A soggy one, but toast nonetheless. But do check if you are not slowed down by wind and waves. Then you need to correct your earlier drawing. __________________ My site downloads: https://ricojansen.nl/downloads Last edited by Pisces; 05-07-09 at 12:13 PM.

05-07-09, 09:22 AM	#3
vonCrandall Mate Join Date: May 2009 Posts: 57 Downloads: 94 Uploads: 0	Sorry, forgot the link. It's there now. My question is - what needs to be changed (if anything), if the intercept will take longer than an hour? I run into a problem when the convoy is VERY far away and obviously using the method linked, estimating 6 knots for them and my 12 knots is only good for an hour (I think). Do i simply need to multiple the speeds verses the estimated time until an intercept?