Checking if your interception course is right

[kstanb]

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?

[palmic]

Originally Posted by kstanb

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?

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 future-one (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 180-90-30=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 180-30-120=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 2-3 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.

[Sean C]

Originally Posted by kstanb

But the challenge is how to know target course and speed from far far away

Originally Posted by kstanb

How far away can you remain without alerting the convoy escorts? how can you add that distance into the calculations?

These problems can also be solved on a maneuvering board, if you're interested in that method. The link I provided above to the manual explains it all, but I'd be happy to help if you have any questions.

[kstanb]

Originally Posted by Nathaniel B.

These problems can also be solved on a maneuvering board, if you're interested in that method. The link I provided above to the manual explains it all, but I'd be happy to help if you have any questions.

My first question is:
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

[Sean C]

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

[palmic]

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...

[kstanb]

Originally Posted by Nathaniel B.

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

No worries, still any chance you can post a clean version of the board?

Also, if you have time, would you solve the following scenario in the maneuver board:
same idea as before, the contact is at 20 degrees heading, 20K meters away, course is 100 and the speed is 8
your maximum speed is 15 knots, your cruise speed is 12 knots

how would you intercept it, optimally, if you want to be at least 8km away until you reach your desired periscope position (this so that it won't spot you during your cruise?

thanks again!!

[palmic]

Originally Posted by kstanb

No worries, still any chance you can post a clean version of the board?

Also, if you have time, would you solve the following scenario in the maneuver board:
same idea as before, the contact is at 20 degrees heading, 20K meters away, course is 100 and the speed is 8
your maximum speed is 15 knots, your cruise speed is 12 knots

how would you intercept it, optimally, if you want to be at least 8km away until you reach your desired periscope position (this so that it won't spot you during your cruise?

thanks again!!

When you already see your target and you know their course, you dont need to calculating anything.
Just set the same course with higher speed and put him behind enough to have time to prepare and then set course to get closer and closer to his track.
When you think its close enough, turn the sub to have perpendicular course to its course to prepare sub to best firing position and tune distance from periscope depth as he is closing..
(for instance if their course is 100, you'll have to prepare sub to course 10 and wait until he will be before you)



Until you see your target
So here you have this triangle:
AoB (angle C) = 100 degrees (angle between his course and the bearing of 20)
his speed (side b) = 8
your speed (side c) = 12


What you want here is the angle between the bearing which you see the target and your desired course (angle B)
The law of sines for angle B here is that:
b/sin(B) = c/sin(C)
8/sin(B) = 12/sin(100)
8/sin(B) = 12/1
8/sin(B) = 12
sin(B) = 8/12
sin(B) = 0.7
B = 45 degrees

So your desired course to meet your target by the speed of 12 kts is the current absolute bearing + 45 => 20 + 45 = 65.

You can see here that since you have your target with AoB about 80-100 degrees, you can calculate the sine of angle between the bearing and desired course simply as his speed / your speed.
Its about 10 seconds to get your desired course..
You can round sines to whole numbers, theres no need to be very precise since your input data are also rough. Try it and youll see it works.