The Silent Hunter 4 TDC discussion
 

TDC instructional video:
http://www.subsim.com/radioroom/showthread.php?t=108689

Well, they almost got it. Almost. They made one small mistake which however has a big negative effect on the usefullness of the position keeper.

Take a look at the lower dial of the position keeper. You will notice it displays and updates the GYRO ANGLES (just like the green line on the attack map) but instead it should be the TARGET BEARING.
There are two ideas behind the position keeper: It should continuesly update the fire solution, taking ownship movement into account (which it does perfectly), but it should also continuesly provide the target position (via bearing and range). Without a bearing readout, we miss a MAJOR feature of the TDC: iRL and in SHI, you were able to CHECK your fire solution after entering the data by watching whether or not the actual target bearing that you can see through the scope and the TDC bearing readout stayed the same. If those two bearings started to drift apart, you knew your solution was not the best, and the faster they drifted apart, the worse it was and you knew your torps are going to miss. If it stayed the same or differed only slowly, you knew the solution was pretty accurate at least if you fire soon and the range was not too great in the later case (when differing slowly).

If the solution was bad, you could easily adjust it by changing target speed, i.e. if the target crosses your periscope bearings faster than your TDC showed, you had to increase target speed for example and vice versa.

The funny thing is that actually in the manual of SHIV when you check the TDC description section you will read them describing that possibility of "checking" the accuracy of the solution and INDEED, where we now have the Ship name read out in the header above the two dials, on the pic in the manual there is this readout: "Target 10, 010" and indeed the lower dial also shows the bearing of 010, not GYRO ANGLES as it does now. It baffles me that they changed that and I wonder why.

A small work around might be to note the difference between gyro angles and actual bearing and watch out that this difference stays the same, however this is inaccurate, needs you constantly calculating and would work only for a rather short time since the difference *must* change over time.


Otherwise I think the game is in fact awesome. Especially cause I didn't even know if it will run at all since I'm only on 1.8 GHz, 512 RAM and 9800Pro, but in fact it runs better than SHIII for me (time compression way better, loading times shorter, runs fluid with some settings I don't care for anyway turned off and the gfx card tuned for performance in the control panel). But I hope they correct the TDC, because being able to actually check your solution for accuracy before firing was a MAJOR feature iRL and in SHI.

I'm not sure I get the problem right

The arrows superimposed on the lower dial mark the gyro angle for the selected torpedo tube.

But the bearing to the target is read on the top of the line. Draw a line between the centers of the upper and lower dials and the intersection with the two dials will give you the AOB (for the top one) and the bearing (bottom one).

On a dial, read the "relative" value on the inner ring, and the "absolute" value on the outter ring.

See this scan from Norman Friedman's book "Us submarines" through 1945".

http://img104.imageshack.us/img104/6...9804bs7.th.jpg

Holy crap. That might well be right. I'm not sure if I'm with you, but I have some idea and will have to check it out asap.

Thanks for providing the image scan! Too bad sims do not come with proper manuals anymore, might have spared me from possibly submitting false claims.

If a mod reads this, please go ahead and flag the topic as "Resolved" or something, since my change of the header is only visible inside the thread. Thanks.

Nope, I'm afraid my initial observation is indeed right. I just checked it out again in-game. Take a look at the image scan elanaiba provided. What we do have on the position keeper in game are the two lower right hand dials. What we do NOT have is a RELATIVE TARGET BEARING (not TRUE BEARING) readout, something similar to what you see on the right hand side in the upper half of the image - actually a numerical readout where it says "Bearing Degrees". We need a TDC output for relative target bearing so that we can compare relative (sighted) target bearing with computed relative target bearing. When you look at the image scan again, you can even see a "Bearing Error" readout which assisted in determining the solution error. We don't neccessarily need this since it would be redundant, but sure enough for the position keeper we need a RELATIVE target bearing output.

Hasn't anybody else noticed this or am I really missing something here? SHI had it, too, as a numerical readout similar to the one in the image.


In fact I think what elanaiba said might indeed be right, I will check again some time later, but then it is a VERY arkward and highly inaccurate (since hard to read) way for the game to provide relative target bearing, especially when we are talking about small deviations between sighted and computed relative bearing which is the nature of the whole checking technique.

You're absolutely right. It would be awesome to have a way to check your solution without having to fire a shot aswell.

I have to admit, I was concerned there would be some mistakes going from the U-boat TDC to the US TDC, being that SHIV seemed more or a less a re-dressing of SHIII. I hope they resolve it soon. Things like this makes the difficulty in finding the game not so frustrating.

Yes, and it's also how they did it iRL. ;) It was the second most important function of the TDC.

At first I didn't notice it and thought "hey look, seems they got it right", but then after I entered the data for my first target (I went right into the campaign), I was like "Uhm. OK, now where is the bearing? Where is the bearing readout??" ;)

Really, what makes me wonder the most is when you check out the manual and look closely at the image provided in the TDC description section, you WILL see a numerical relative target bearing readout in the "header line" where we now get the ship type provided instead after ID'ing, and they TALK about the Position Keeper helping in checking and fine-tuning the solution.

heartc,
It would help a lot if you could post some images of the issue.

The distances of ships was confusing to me... I would look... and it would be like 2k... then submerge moving in the same direction, surface and all the sudden be like 6k behind or something, and they were not moving fast....

Hmm..

Would love to hear Neal's comment on this.

I'm at work right now, but I wouldn't really know how to visualize it anyway. Basicly, what I'm saying can be summarized in that we need a target relative bearing readout (at best numerical / "digital"), as you can see in the scan above.

I mean, this is the *position keeper*. How do you pinpoint a position? By bearing and range. The position keeper is not really wrong - it's working perfectly - it's just that an essential readout is missing. It shouldn't be too hard to add this since the target relative bearing must be known and updated by the position keeper already as it is now, otherwise it wouldn't work at all. It's just that there is no proper readout for it like there was iRL and in SHI. And when looking at the manual it seems like there once was such a readout in SHIV, too.

You do have a bearing readout, just as in the war versions of the TDC.

http://img152.imageshack.us/img152/5688/tdcstuffam2.jpg

I think there's a bug, though, and the position keeper will not update the bearing once you use the periscope lock feature. Try to just attack ships without the lock, and see if it works correctly.

Well, I already thought that this is what you described in your initial response. However, if that is all there is, it is a highly inadequate and gross method of displaying relative target bearing to check for solution errors, especially on a tiny PC monitor. From your image scan and SHI, I got the impression that iRL they indeed had an additional numerical bearing readout. Did anyone check the manual yet and is seeing what I'm seeing there?

The real US TDCs that I've seen in pics didn't have the digital readout for bearing error that Friedman has drawn there.

Granted, they had a second relative bearing dial (actually a pair) which helps to read it precisely. But the interface in the game was meant to be kept simple and straightforward.

Perhaps the future will bring a clearer readout.

elan,

I'm not sure what you are saying makes sense, or I'm mis-understanding you.

Examine the pic of the SHIV TDC. You are saying that the relative bearing is read from the inner dial, but from what index? As far as I can tell, the inner ring of the lower dial is a fixed compass rose around your ship, and the "arm" moving across your bow is the gyro angle of the solution as read against that inner ring. In your example, the relative bearing is reading zero, but It will *always* read zero....

Edit: Ahh, it seems that the outer ring of the bottom dial represents true heading of own ship. It's basically a compass when read against the inner ring "ownship" image. So, that sums up the bottom dial... ownship heading on outer ring, gyro angle on arm.

That leaves the top dial yet to be understood by my challenged brain hehe.