trying to understand SH3 TDC

[AdamMil]

I'm trying to understand the TDC in SH3. I was playing with it, and the results are quite different from what I expected. Can somebody enlighten me as to how it works?

Here's what I expect for a very basic setup:

http://i18.tinypic.com/66jtap0.png

However, look at the TDC for 60 and -60 (300) degrees of bearing.

http://i12.tinypic.com/4lr62j5.jpg
(60 degrees of bearing. Note that the impact point is inside the circle.)

http://i11.tinypic.com/4v5dv9z.jpg
(-60 [300] degrees of bearing. Now the impact point is way outside the circle.)

Although the estimated impact points are different, they may in fact be going through the paths I expected. But why would it be 33 seconds to impact on one side and 19 seconds to impact on the other, if it's the same range? The torpedo speed is the same between the two (as you can see in the inner speed dial), so I don't get it. :-(

[raduz]

you are right, I have tried it too and it was the same. I dont understand why... perhaps try to edit a test mission with a target at your 60 degrees port/starboard in order to find out whether the solution really works.

however, you will never fire under such angles (-60 and +60). The best shots are within +10/-10 degrees max.

[Hadrys]

however, you will never fire under such angles (-60 and +60). The best shots are within +10/-10 degrees max.

Wanna bet? I do shots at 90° and AOB would be around 250° so the torp would have space to make a turn.

[AdamMil]

Yeah, I don't fire at +/- 60 degrees bearing -- I'm just trying to understand how it really works so I can switch to manual targetting. :-) I know there are tutorials, but I'd really like to know how that thing really calculates the gyro angle and impact point, so I can understand the reasons behind the steps in those tutorials...

[Hadrys]

Yeah, I don't fire at +/- 60 degrees bearing -- I'm just trying to understand how it really works so I can switch to manual targetting. :-) I know there are tutorials, but I'd really like to know how that thing really calculates the gyro angle and impact point, so I can understand the reasons behind the steps in those tutorials...

My advice would be not to think too much about TDC and simply practice with different settings and angles with T1 torps and watch how they go, where to shoot without any tdc settings to hit the target. You know that the target is doing ~6kts (slow simply) and it's "that" huge in your scope so you place your eel 20 degrees in front of it. Than you can compile normal targeting (range, aob, speed) and compare visual observations with bearing given by TDC. I would say a trained eye is most important in manual targeting, plotting is secondary (I don't do any currently).

[joegrundman]

I don't really understand what you are saying there Hadrys. Of course the TDC is useful to use, not especially difficult to understand, and perfectly accurate. Your suggestion seems only to apply at very, very short range.

I do not understand the difference in TDC solution, as shown. That must be an error somewhere, either in the game or elsewhere. Is it always like this? From the mathematics of this, the TDC should not express a difference between shooting to port and starboard. The marginal difference in the position of the bow tubes I doubt can account for this variation.

Nonetheless, it makes no difference when using smaller gyro angles.

As for how the TDC works:

The German TDC, unlike the US one, does not update range or changes in your own course. However, in some ways this disadvantage is actually an advantage, as certain aspects of the TDC will remain solved for all members of a convoy, so long as nobody's heading hasn changed.

This is the torpedo fire control problem in detail:

http://img117.imageshack.us/img117/369/torpedoproblempn1.th.jpg (http://img117.imageshack.us/my.php?image=torpedoproblempn1.jpg)

The TDC does the hard work of accounting for z,m and p, which is respectively the turning circle of the torpedo, the initial straight run of the torpedo before beginning the turn, and the torpedo tube parallax, the difference between the relative view from the periscope and the fact that the torpedoes exit from the front or back of the submarine.

So apart from that, you need to know the relative bearing to the target (the periscope angle), the relative course of the target (which is related to the AOB), the speed of the target and the range to the target.

Look at the AOB dial on the TDC. The "north" point of this dial represents the targets relative course. Let's imagine you are stationary lying ahead of the beam of the target, i.e. perpendicular to the target track, but before the target has reached it. You can see that in your mind, so long as neither you, nor the target change course, then as the target moves forward, the pericope angle to it will approach 000, and likewise the AOB of the target will move towards 90.

The rate of change of both is identical and this is reflected in the TDC. The AOB on the TDC once set, ie. the autoupdate light is on, the AOB will then automatically update with any change in the position of the scope.

This means that so long as neither you, nor the target chancge course, your AOB solution will be correct for every ship following the same course. A convoy, for example.

This is entirely independent of changes in range or changes in speed.

Warning! Entering AOB via the notepad on the periscope or UZO screen can be risky, and if you have time you should always update it from the TDC screen.

The reason is that the TDC AOB will update with changing periscope angle, but the notepad will not. If you enter an AOB from the notepad, that will remain on the notepad, and if you send a new range from the notepad, you may accidentally send your old, and now out of date, aob with it.

[Hadrys]

I don't really understand what you are saying there Hadrys. Of course the TDC is useful to use, not especially difficult to understand, and perfectly accurate. Your suggestion seems only to apply at very, very short range.

This is WW2 so close range is your friend. This is why they invented FAT torps to increase a chance of hitting far targets. What I wrote works for me up to 1000-1500m for lonely ships and I had great successes with convoys up to 3-3,5kms. Also very useful against circling DDs where you have fractions of seconds to send a deadly eel. Of course best is <1000m for precise targeting. In general a chance of successful hitting a ship with single eel at 4kms even with the best data gathered (TDC) is rather a matter of luck. It's very very easy to produce minimal errors which cause an eel to pass 2 meters from the ship...

[ichso]

It's even not historical that u-boats used map plotting for their attacks. They used a device like this: http://subsim.com/radioroom/showthread.php?t=114351&highlight=whiz+wheel

Play around with the TDC and you will also recognize that (with every other setting fixed) the target's speed has a major impact on the calculated gyro angle. Small errors in AoB and range produce way less differences in the shot direction.

Get as close as you can for your attacks, at best under 1km. Of course this depends on escorts nearby, visibility etc, too.

This strange thing with the time on impact mentioned above doesn't disturb your shot's precision.
Try to keep the gyro angle < 10°, it doesn't matter whether you have the target coming from port or starboard.

Although this sounds really strange, indeed :hmm: Never realized before.
Thanks for the input ;)