Convoy interception tutorial.
 

Hi all, I'm a new to this forum.
I've read some of threads and the one, devoted to guides and trainings also. I didn't find any guide of convoy interception step by step, so I've decided to make one.
Found some info, taken from german manual, but it lacks the "exact" solutions - you have to make some iterations with all this circles and all... So, I did it in another way.

If it was a wrong decision and my topic is repeating somebody's else guide, that I've didn't marked - so, sorry.

Ok, here we are.
http://img214.imageshack.us/img214/3...cture01kx6.jpg
1. We've recently got a radio message with coordinates of slowly moving ship near us. She's heading south.
First of all, draw a line with ruler along his supposed course. As long as you want.
http://img214.imageshack.us/img214/323/picture02tc1.jpg
2. We know that speed of our target is "slow". For transports this often equals 7 knots. We'll take the scale 1 km = 1 knot.
So, draw the circle with radius 7.0 km.
http://img201.imageshack.us/img201/5...cture03if3.jpg
3. At the same time we want to be at ship traverse some time before him. We can trade distance on time. I think, 7 km would be enough (for making corrections of merchant estimated course and coordinates, cause radio messages only gives its rough estimation and to submerge in position). If it was convoy, then a distance would be greater - cause of destroyers screens there is need of more accurate choice of position.
So, we move 7.0 km circle by 7 km along merchant course. Now the center of circle is the virtual point ahead of merchant. Call this point A.
http://img201.imageshack.us/img201/4...cture04nx3.jpg
4. Now, I connect this point A with my current position, which I call B.
http://img201.imageshack.us/img201/952/picture05ol6.jpg
5. Here comes question - at what speed we want to go in place? We're not so far from this target, so it wouldn't take much fuel if we choose go at flank speed. At flank we do 20 knots (remember, 1 km = 1 knot in our scale). So, draw the 20 km circle with center at the end of the first circle with radius touching the line AB.
http://img201.imageshack.us/img201/4...cture06qx9.jpg
6. Greetings, we've got our magic direction! At this point we need to offset resulting circle so it touches with end of this radius our current position, due to the lack of parallel ruler instrument in game.
http://img201.imageshack.us/img201/9...cture07gk9.jpg
7. Now, plot our course along this "magic radius" until it crosses merchant course line.
http://img201.imageshack.us/img201/9...cture08dx3.jpg
8. When I'll get here (56 km at 20 knots wouldn't take much time - only 1:30) - I'll turn on radar, or submerge and use hydrophone to define merchant course more precisely. But it's a different topic, however.
This method works, as the vector algebra does.

Now, some remarks.
1. If you can't get the solution so that circle with your potential speed can't touch the line "AB" it means that you can't get here in time. Try to increase your speed (i.e. circle), or give up from this target.
2. Target speed estimations.
If it's a convoy or task force - you always get their speed with Radio Message. 12 knots, 9 knots and so on. So you know it. In case it's a "ship" (often a couple of them without any escort) - then "slow" often is 7 knots, and "medium" - 9 knots.
I'm speaking about clean game, without any mods.
3. Often you wouldn't go at flank, in such cases you draw not 20 km circle, but one corresponding to your speed. If you go at 13 knots - then it would be 13 km (in 1 knot = 1 km scale).
4. Intercept ships that are heading towards you, not those who are getting away.
5. When plotting such solutions on great distances (more than 200km) you can take more comfortable scales - 1 knot = 10 km, and so on.
6. Sometimes I've encountered small convoys (with passenger liners) that changed their courses, and very roughly. Turning at more than 45 degrees - when I've ended my route in place. Maybe they were detected emission of my radar, I don't know it. So I think they could change their course in route. Sometimes (when intercepting on long ranges - more than 500 km for a long time - more than 24 hours) I lost some convoys - in a point there was no one ship. But it was not so often - only a couple of times in two careers, so I was surprised, but not disappointed cause to this time I got another RMs with other ships coordinates.

Thanks for reading it.

hey nice job :up:

I always just guesstimated my long intercept paths but sometimes made miscalculations that could take hours to rectify. This looks really useful!

If you're interested...

I have a vector math tool that solves that problem (among other things) in about 5 seconds. :ping:

http://www.xl-logic.com/mobo/tutoria...t_20070801.png

Good Job!

Thanks for taking the time!

I for one would be interested in that tool. Where can I find it??

Thanks ................ Hitech

Just stop by the MoBo forum, there's a link in my signature.

Thanks :up:

Nice tutorial! :up:

I just wanted to thank aaronblood for mentioning "MoBo".
Personally I think the use of "electronic maneuring board" is somearound "incompatible" with "realism" of times WWII. There were only those dividers, circles, protractors,.. and skills of weapons officier, navigator and Herr Kaleun at solving those problems :)

And I think, they knew the formula

beta = arccos{sqrt[1-(vt*sin(alpha)/v)^2]},

where beta is the angle of interception (counting from 0 course),
vt - target's speed,
alpha - AoB of target,
v - speed of own vessel,
and they used it too (as TDC does) with graphic solutions on paper Maneuring boards.
Yeah, I think they plotted much and were true guru in planar geometry, the masters of ruler and circle :)

Of course, everybody makes his choice, and I have nothing to say in offence at you :).

Also I remark there is a good piece of interesting material in MoBo manual.
From there I've got a great idea of how to get the course of target by using just hydrophone. The key is prediction of bearings and triangulating by those (it was a fresh idea, I always guessed target's speed) after reading section concerning "Advanced TMA" at the end.
Maybe I'll find some time to create a different tutorial with screenshots conserning solution of this task - in terms of using the ingame plot tools (which are similar to real ones instruments), without switching to other programs (and "using techs of future" ;) )

But it's the other topic, however.

I don't think I've modelled anything in MoBo that a WWII tracking party wouldn't have access to. Granted, I've provided a few shortcuts for the tedious parts, but you're basically just drawing vectors on a map.

Glad you found the TMA info useful... here's a link to a tutorial thread on advanced TMA with MoBo: Advanced TMA

beta° = (180/pi)(arccos{sqrt[1-(vt*sin(alpha°)/v)^2]}),

where beta° + bearingTotarget° := interceptcourse°,
vt:= target's speed,
alpha°:= AoB of target
v:= speed of own vessel,
pi:= 3.14159265

Gonna have to try it out. Been using Wazoo's method.

In any case, all those methods are just for getting and idea on how to screen a convoy or ship from afar, and positioning your boat into an optimal firing position. The actual firing procedure can be entirely (or semi-entirely, if you want an AOB that is close to perfect) by visual means. So I never felt the need of such an extremely tidy method for following a convoy.

Sliced bread is almost as good as MOBO, created by our in resident genius, aaronblood. (psst. aaronblood, you haven't forgotten that I was and am still MOBO biggest fan? It is incredible.)