SUBSIM: The Web's #1 resource for all submarine & naval simulations since 1997 
020816, 12:34 AM  #1 
Frogman
Join Date: Mar 2010
Location: São Paulo, Brazil
Posts: 300
Downloads: 421
Uploads: 0

Checking if your interception course is right
This aviation website might come in hand. Just ignore the wind page and insert the fields with the data you gathered from a convoy or a single ship. Just add some extra knots on ownship to arrive before and have time to setup your attack.
http://www.luizmonteiro.com/RA.aspx 
022016, 10:47 AM  #2 
Grey Wolf
Join Date: Jan 2014
Location: 50.1° N, 14.4° E
Posts: 832
Downloads: 73
Uploads: 5

You can do it even in old fashion way (like real sub captains did) with good ol' paper and pen like this:
As your approach to the ship is triangle (as basically everything what you will be solving in ubote ), you can describe it like triangle ABC where A is your position, B is collision point and C is current position of your target. In this triangle opposite side to target position (C) is side c  your path to collision point (B). Your task here is to solve angle at point A (your position) when you know target course and speed and you pretend you want to choose your speed. In this example lets say target course is 100 and speed is 8kts Your REAL bearing at which you hear it is 20. (real bearing means bearing at hydrophone + your current course) The speed we want to maintain is 12kts (it means we want to flow at medium speed at surface). So what we have here is triangle ABC with a=8, c=12. A=?, B=?, C=10020=80 degrees The law of sines says that we now have all mandatory input to find our desired A angle which solves our desired course to collision with the ship. Its: "If you know either (1) or (2), you can use the law of sines to solve the triangle." We actually knows (1). So: a/sin(a) = b/sin(b) = c/sin(c). This means: 1) a/sin(A) = c/sin(C) 2) 8/sin(A) = 12/sin(80) 3) 8/sin(A) = 12/0.98 4) 8/sin(A) = 12.24 5) sin(A) = 8/12.24 5) sin(A) = 0.65 6) A angle is 40.6 degrees 7) our desired course has to be real target bearing + A angle => 20+40.6 = 60.6! So if you have good target speed and course and you want to crash that ship directly to bow, order your navigator course 61 and wait few hours until you see the vessel! If you want to be there in advance, just calculate with position of the target the same time in advance (when you'll get into this, you'll start to use trigonometry to find out at which bearing you'll here it next hour pretty simply) HINT: If you want to reorient the equation at 1) to solve the angle at once, its like that: sin(A) = target_speed / your_desired_speed * sin(angle_on_bow (C) ) (which is basically equation to solve it all!!!) Your task now her Kaleun is to solve the distance you will have to reach to collision point by the law of sines or law of cosines. This means you'll have available even time to reach the target. And then you could start to grow your beard for sure (and you can even stop to use navigator fixes, cuz you'll have better precision ) For this, we need to have another input data and thats current distance to target at that bearing we hear it. Let's just say its 20.000 meters for now. What will be distance to collision point? BTW: As every inside angles of triangle summarized gives always 180 degrees, you can solve angle B pretty easily as 180(60.6+80)=39.4 If you tried to attack ship in nonright angle by torpedo, you should already know, that its basically angle of track which could solve your torpedo solution if you are already in attack phase! So this simple equation could literally gives you TDC inputs solution at max realism! Last edited by palmic; 022016 at 11:50 AM. 
022016, 06:04 PM  #3 
Frogman
Join Date: Mar 2010
Location: São Paulo, Brazil
Posts: 300
Downloads: 421
Uploads: 0

wow thanx palmic for such wonderful info. I was planning to ask the manual procedure in a sailing/navigation website but you were faster
I'll try it at home with very very enthusiasm... 
072417, 05:27 PM  #4  
Sparky
Join Date: Mar 2009
Location: Toronto, Canada
Posts: 153
Downloads: 105
Uploads: 0

Quote:
Scenario is, you get "smoke in the horizon" message: single ship or convoy it doesn't matter, you get heading to the target and you can additionally ask for a rough estimate of range; normally in the 9000 to 12000 range. With target identification disabled, I can't even use the stadimeter. so my normal strategy would be to close at flank speed. Problem is that then by the time I am close enough to identify it and get a first course and speed estimate, I am actually too close now, so no longer "enough time to grow a beard" scenario. And being close means that there is a chance he will see me and in that case, he will change speed and heading again 

072417, 06:06 PM  #5  
Grey Wolf
Join Date: Jan 2014
Location: 50.1° N, 14.4° E
Posts: 832
Downloads: 73
Uploads: 5

Quote:
You can get bearings by hydrophone or visualy, doesn't matter 

072417, 10:52 PM  #6  
Sparky
Join Date: Mar 2009
Location: Toronto, Canada
Posts: 153
Downloads: 105
Uploads: 0

Quote:
Thanks a lot 

072417, 11:10 PM  #7 
Grey Wolf
Join Date: Jun 2017
Location: Norfolk, VA
Posts: 840
Downloads: 12
Uploads: 2

This might be of interest: NIMA Maneuvering Board Manual
You really don't even need the fancy "Maneuvering Board" sheet. A ruler and protractor on a sheet of graph or even plain paper will do just fine. 
072517, 05:12 AM  #8  
Grey Wolf
Join Date: Jan 2014
Location: 50.1° N, 14.4° E
Posts: 832
Downloads: 73
Uploads: 5

Quote:
You can off course draw it to map, but i like more to write few equations on HW paper. Its just triangle with one side (target course with length of target speed, e.g. 6) and second our speed, all angles are already known in this situation (AoB, bearing of target from us, and the third is always 180both others). With this, you can simply find solution by the law of sines 

072517, 07:14 AM  #9 
Sparky
Join Date: Mar 2009
Location: Toronto, Canada
Posts: 153
Downloads: 105
Uploads: 0

And how do you work the stealth factor?
assuming day time, with good visibility, you can't just get into a perfect intercept, without being spotted. How far away can you remain without alerting the convoy escorts? how can you add that distance into the calculations? I think I like the idea of plotting an intercept based on a slow speed (like convoy is doing 8 knots, so plot an intercept at 10 knots, but then run at flank speed to arrive much earlier), this way I am relatively far away until I reach intercept, then periscope depth for final adjustments... thoughts? 
072517, 08:04 AM  #10 
Grey Wolf
Join Date: Jun 2017
Location: Norfolk, VA
Posts: 840
Downloads: 12
Uploads: 2

Here is the solution to your example problem on a maneuvering board.
The red line (em) is the target's true course and speed: 100°, 8 kts. (The speed scale used is 2:1, so the line is drawn to the 4 circle.) The blue circle is our desired speed to intercept: 12 kts. The dashed purple line is the target's bearing: 20°. We want to move in the direction of the target, so we draw a line parallel to the dashed purple line from the end of the targets course and speed vector: this is the solid purple line (rm), which is the desired relative motion vector. We then draw a line from the center (e) to where the rm line intersects our desired speed: this is the green line (er), which is our required course at 12 kts. As you can see, it is indeed 61°. Now, if we measure the length of the relative motion line (rm), we can determine our relative speed. If you look at the bottom of the 2:1 scale on the far left, you will see that the relative speed is about 7.6 kts. Supposing the target is 20,000 meters away, that equals about 21,800 yards. Using the nomogram at the bottom, we draw a line from the relative speed (7.6 kts.) through the distance to close (21,800 yds.) and arrive at a time of about 85 min., or 1 hour and 25 minutes. The actual distance traveled can also be solved on the maneuvering board, but I didn't want to clutter it up too much. 
072517, 08:06 AM  #11  
Grey Wolf
Join Date: Jan 2014
Location: 50.1° N, 14.4° E
Posts: 832
Downloads: 73
Uploads: 5

Quote:
You have more options, i would pick one of these: 1) if you want to be "scientificaly" set, you can check ingame speed table and check how far they will get after lets say 15 minutes which you want to have in advance for your final targeting from periscope depth... Then you just recalculate the triangle with their current bearing from you moved from current to futureone (where they will be after 15 minutes), so your calculated solution will be with these 15 minutes in advance and you will be at collision point before them. 2) But i am rather much more lazy to calculate and rather follow the first calculation and i set a little quicker speed than i used in calculation. (You should not use flank speed if you want to be authentic, because flank speed in reality of ww2 overheated engines and they would require some maintenance then...)  If i would get close enough to see the ships from distance i would just set the same course i know they have and move before them. As you know their course, you know virtualy even their current angle on bow and of course the bearing which you see them at, so you know naturally even the third angle  the angle of tracks if you turn your boat to their course (to get closer). This way i like to get lets say to move them to my bearing of about + 120, or 240  depends on if i have them at port or starboard. So if i have them at 120, i am a lot before them to start to approach closing course  i order 30 degrees to starboard  and they move logically from bearing 120 to 90, because i turned by 30 degrees to the right.. So i know that our angle of tracks is 30 degree (because i had the same course and turned by 30 to closing them), bearing at which i see them is 90 so their current angle on bow has to be 1809030=60. With intercept course set i just check if i keep them at my 90 or even moving them even more behind to 90+.... This way i know i am on my way to get to firing position in advance. If you have distance from them you can even calculate how distant they would be before you in future if you would just stop and wait for them here  its current distance * sine(current AoB). If their current AoB is 60, it means it would be current distance * sine(60) > current distance * 0.9 (one decimal is enough in these equations...). So  my task here would be just to lower their current AoB to me, which is automatically happening as i am closing to their track by angle of 30 degrees. If i am quick enough, i will eventually see them at 120 again and this means  if i still have that 30 angle of tracks (closing to them by 30 degrees at collision point), that current AoB is 18030120=30  AND THAT MEANS  current distance * 0.5. (sine of 30 is 0.5) SO! If they are about 15km out of me, they will be just 7500m away if i will stop here! And so on. Just keep in mind this very simple triangle and you will always have situation under control, because this is what ultimately is happening in this approach situation. Just check where you have limit of bearing where you see your target because you can of course get behind their track if you will not stop in time... In this situation  30 degress angle of tracks, if i would get them to 150, i would be actually inside their track (150+30=180  there is not even one degree remaining for AoB > this means current AoB is exactly 0!  they are just moving directly on me..) In nature its very simple and you can even calculate this things in head just in few seconds, you just have to get used to it. Forget map, forget geometry and just remember all angles in the triangle gives sum 180, thats all... Always get course of your target from distance if you can, and you have practically everything.. By the course you can even very effectively get their speed visually, just get close enough to see at least their smoke, set the same course, and change speed to fix the bearing which you are seeing them  if you manage to keep them at the same bearing for 23 minutes, you have the same speed ... and maybe check even "How to prepare torpedo Attack with basic trigonometry" in my footer, there's more uses for these rules which will help you to realise how this works.
__________________
Check my mods (Downloads tab) uboats documentaries 1) Real navigation  target motion analysis cheatsheet 2) Real navigation  Perfectly controlled approach 3) Real navigation  How to prepare torpedo Attack with basic trigonometry Really needed: Learn RAOBF optical targetting Last edited by palmic; 072517 at 10:16 AM. 

072517, 08:29 AM  #12  
Grey Wolf
Join Date: Jun 2017
Location: Norfolk, VA
Posts: 840
Downloads: 12
Uploads: 2

Quote:


072517, 10:30 AM  #13  
Sparky
Join Date: Mar 2009
Location: Toronto, Canada
Posts: 153
Downloads: 105
Uploads: 0

Quote:
Do you use the board in game? I opened "toggle chart visibility", then looked for plotting tools, maneuvering boards Then I centered it in my last know position Challenge is: I cannot write on top of it, is this something that can be done? it was not too difficult to replicate the circles and protractor to get the 61 degree heading, and there is a nomograph just in the right side of the map, but I still don't know how to get the 7.6 relative speed using map tools EDIT: I just noticed it is a given; I thought you had to graph it, but I can see now that it is actually just a matter of counting the 4 lines EDIT2: Wrong again!, the line you need to draw to get 7.6 is from m to r... I now get it... however, with the drawing tools and really small maneuver board available in game, it might be challenging to get anything accurate.. Can you attach a "clean" maneuver board file? I like the high resolution of your example... worst case I can still print and draw manually Last edited by kstanb; 072517 at 11:10 AM. 

072517, 10:37 AM  #14 
Grey Wolf
Join Date: Jun 2017
Location: Norfolk, VA
Posts: 840
Downloads: 12
Uploads: 2

TBH, I've never played any version of SH, so I can't answer that.

072517, 11:11 AM  #15 
Grey Wolf
Join Date: Jan 2014
Location: 50.1° N, 14.4° E
Posts: 832
Downloads: 73
Uploads: 5

Just use "E" key to toggle the chart. Toggle off to pick first point of line, then toggle chart on, move cursor to desired position, you know...

Thread Tools  
Display Modes  

