TDC

[captcrane]

Ahoy Guys. I have been using manual targeting for some time. But I have a question I was wondering if someone could clear up. My steps are as follows even before I see the target . #1 speed of target. #2 set periscope to 0 degrees. #3 Press L key #4 set angle on bow #5 Set range (dragging dial clockwise). The question is step 3 necessary? and my follow up question would be. If I turn the periscope say 25 degrees starboard then dragged the range dial would that change the course of the torpedo?

[Rockin Robbins]

Haw! Haw! You've come from U-boat land, haven't you! Well, from your point of view the American TDC is just screwey. The best thing I can tell you is to watch the Sub Skippers Bag of Tricks thread for a video which is presently in pre-production on Stadimeter Targeting Technique. But that doesn't exist yet.

Let me see if I can be of any help. Yes, the first thing I generally develop is the target speed and enter it into the TDC. When you turn the dial you must press the button with the triangle on it, the "send to TDC" button twice. That's done.

Now in the course of measuring the speed if you're using radar, you have two position points which can be extended to get you a target course. Now there's a sneaky trick to enter the course into the TDC in place of the angle on the bow and you'll see that in my video, but for now let's sit on that course determination to enter AoB.

We'll do that after we input the range. Hopefully he's too far away and using the stadimeter right now would be a joke. We don't have any tools to automatically send range from radar to TDC and no way to manually enter it. So much for realism in Silent Hunter 4, huh?

But we have a tool for directly entering range from long distance and that is the sonar. Have the sonar operator give you the bearing, then ping that bearing manually, then hit the send range to TDC switch and the send bearing to TDC switch. Done.

Now go to the nav map. With the protractor click on the course ahead of the target, then again on the center of the target, and finally on the center of your submarine. The angle you read is your AoB and the side of the target you can see from your sub is how you determine starboard or port. Enter that on the dial and press the send button twice.

Now immediately turn on your position keeper. Time for a little theory.

The German TDC works by pointing your torpedo at a point ahead of the target. When your target gets to your predecided shoot bearing you press the los button and the torpedo zips out there. This is like shooting at a duck by holding your shotgun pointed at a point and waiting for a duck to be the proper lead angle away. It's a timing shot.

Well the American TDC doesn't work that way, at least not when you're using the position keeper. It uses the equivalent of pointing the shotgun ahead of the duck and maintaining the correct lead angle at all times by sweeping across the sky ahead of the duck. The advantage is that you can shoot any time you want and hit your target.

If you go to the attack map, you can see the comparison between the real position of the target and where you told the TDC the target is. The position keeper also moves the artificial target on the course and at the speed you specified. Is the x superimposed on the target? If not, is it on a straight line between you and the target, very close to the target? That's a probable hit.

If you examine the end of the torpedo track you'll see a number, and that is the time of the torpedo run. To have a hit, the x marking the aiming point of the TDC must remain on the target for that length of time. If it won't do that you have to analyze what you see.

It could the that AoB is slightly wrong. In that case the x will move at the same speed as the target but drift to one side or the other. Go back to the plot, remeasure the AoB, set it on the dial and press "send to TDC" twice. You don't have to do anything with the position keeper button.

If the x is moving on the same course but lagging behind or forging ahead of the target your speed is wrong. Go to the TDC and add or subtract a knot from the speed, press "send to TDC" twice and go back to the attack map.

It should be much better now. It doesn't have to be perfect, just keep the x superimposed on the target for the time of the torpedo run. Get him under 700 yards. You can shoot at any time and hit the target. It's always good to check your solution just before you fire.

Remember, the American TDC has no automatic connection between periscope and TDC. If the TDC has information it's because you manually sent it there.

[captcrane]

Now that's a surprising answer and fast also. I have to rethink everything I thought I knew. I was under the impression that the position keeper and the stadimeter were intertwined. So I never (well not in awhile) used either of those. My ranges with the stadimeter were pathetic. Looks like I can add something new to my game. Currently I am in an S boat 3rd patrol. I have no surface radar but I can detect enemy aircraft. After I get SD radar I will change my game settings to no map contacts because that is pretty much how I am playing now. By the way I am always on the American side ex marine. When I get more proficient at the game going to try RSRD. I am also a citizen of England. Thanks for your input!

[Rockin Robbins]

For some it will be difficult to understand the explanation above. Stay tuned for the video. I'll be asking questions afterwards to try to improve my explanations so everyone can understand just how the (insert appropriate curse word here) US TDC really works. The video and copy of the above explanation will be in my Sub Skippers Bag of Tricks thread.

[ColonelSandersLite]

I thought I would try to word this another way, not saying that anything RR said is wrong though.

There are two major differences between the German TDC and the American TDC. In my book one is a major advantage and the other is a disadvantage required to make the other work.

In the american TDC, the AOB is not coupled to periscope bearing. Moving your scope will not change the AOB. I increased size and bolded there because this cannot be stressed enough. The typical german method of pointing your periscope at 0 and entering the track angle then just point the periscope at the target to get AOB does not work. This is a disadvantage.

In the american TDC, the optional position keeper tracks the target and your own subs movements and updates the torpedo gyro angle in real time, even if you are not tracking the target with any sensors at all. Again, cannot be stressed enough. This is clearly a major advantage.

[Rockin Robbins]

Interestingly, in real life the American periscope could automatically send data to the TDC and would work just like the German one if they so chose. So many things about the real TDC have been nerfed and dumbed down for the game. And radar range and bearing were also automatically linked to the TDC if desired. Plus there were two crewmen tasked with making sure the TDC data was accurate according to the plot and the data developed from sensors.

And ColonelSandersLite, those are the two sentences that will be on the test. Thank you.

[TorpX]

Originally Posted by ColonelSandersLite

In the american TDC, the AOB is not coupled to periscope bearing. Moving your scope will not change the AOB. I increased size and bolded there because this cannot be stressed enough. The typical german method of pointing your periscope at 0 and entering the track angle then just point the periscope at the target to get AOB does not work. This is a disadvantage.

Umm. To clarify about this. The Germans couldn't do this in real-life. The automatic periscope connection did not exist. AoB data had to be manually input by a crewmember; meaning this mechanism is purely a game device, like 'locking' on a target with the periscope.

[ColonelSandersLite]

Didn't know that. Still an accurate statement as far as sh3 and sh4 is concerned though.

[TorpX]

Originally Posted by ColonelSandersLite

Didn't know that. Still an accurate statement as far as sh3 and sh4 is concerned though.

Yes. I dare say most SH3 players don't know it, either. It kind of irritates me when they complain about how the USN TDC isn't any good, because it can't do what the German model does.

[BigWalleye]

Originally Posted by TorpX

Umm. To clarify about this. The Germans couldn't do this in real-life. The automatic periscope connection did not exist. AoB data had to be manually input by a crewmember; meaning this mechanism is purely a game device, like 'locking' on a target with the periscope.

I don't know what your source is for this information, but it clearly conflicts with this site:

http://tvre.org/en/torpedo-calculator-t-vh-re-s3

The site is called Torpedoverhaltrechner Project, and includes an enormously detailed analysis of existing documentation for the Seimens T. Vh. Re. S3, the standard TVR installed on German subs from 1941 on.

A relevant quote:

"In the standard operating mode, after entering the target data by means of the knobs, the calculator (taking into account the current target bearing transmitted from the periscope/UZO and own course received from the gyro-compass) automatically calculated the torpedo triangle solution and the torpedo salvo spread angle." (emphasis added)

I have not found similar detailed analysis of the operation of earlier TVR's, but this source definitely claims that the S3 received target bearing and submarine heading data automatically. Perhaps your source refers to an earlier version. IAC, I would appreciate if you could post the reference. Thanks.

[Rockin Robbins]

Originally Posted by BigWalleye

A relevant quote:

"In the standard operating mode, after entering the target data by means of the knobs, the calculator (taking into account the current target bearing transmitted from the periscope/UZO and own course received from the gyro-compass) automatically calculated the torpedo triangle solution and the torpedo salvo spread angle." (emphasis added)

I have not found similar detailed analysis of the operation of earlier TVR's, but this source definitely claims that the S3 received target bearing and submarine heading data automatically. Perhaps your source refers to an earlier version. IAC, I would appreciate if you could post the reference. Thanks.

You read it wrong. Your quote doesn't say "automatically sent" it says "automatically calculated." And it says "current target bearing transmitted," which begs the question "Transmitted how?" It could be from the periscope directly, very, very unlikely considering the primitive nature of the U-boat compared to the fleet submarine, or, vastly more likely, transmitted manually and then entered manually or entered manually by an orderly at the scope.

So your quote is conclusively inconclusive on the question at hand.

[BigWalleye]

Originally Posted by Rockin Robbins

You read it wrong. Your quote doesn't say "automatically sent" it says "automatically calculated." And it says "current target bearing transmitted," which begs the question "Transmitted how?" It could be from the periscope directly, very, very unlikely considering the primitive nature of the U-boat compared to the fleet submarine, or, vastly more likely, transmitted manually and then entered manually or entered manually by an orderly at the scope.

So your quote is conclusively inconclusive on the question at hand.

Fair enough. So I will add another quote from the same site:

"The current target bearing was entered automatically by means of selsyn links, however in an emergency, it could be set manually using the hand-wheel on the TDC. " (emphasis added)

A selsyn link is a pair of synchronous servo-motors wired so as to maintain the same angular rotation in both motors. The site has both pictures and circuit diagrams of the selsyn sets used in the TVR on U-995 and schematics of the overall system. The circuit disgrams and schematics were reverse-engineered from the existing hardware, which is datable to 1943. The schematics show the selsyns providing a direct link from the attack periscope and UZO stations to the TVR, via the selsyn sets.

Further information from the tvre.org site:

"The aiming and target bearing transmitting subsystem automatically transmits up-to-date target bearing data from a selected aiming device (UZO or periscope) to the torpedo data computer.

"The UZO and both periscopes were connected to target bearing transmitters (Torpedo-Ziel-Richtung Geber). They operated on the selsyn synchro link principle and transmitted the bearing directly to the torpedo data computer. Each target bearing transmitter consisted of two selsyn transmitters in order to achieve better accuracy. First, they transmitted the angle in the range of 0 – 360°, the second – in the range of 0 – 10°. The maximum transmitting speed was 12°/s.

"The aiming device (UZO, attack periscope, or sky periscope) used during the attack was selected (connecting the proper target bearing transmitter with the computer) by means of one of the two rotary switches located at the aiming subsystem control box that was installed in the control room (under the chart table)."

I can not claim to know the accuracy of the information which the tvre.org site presents, but it does clearly and repeatedly claim that, on U-995, which entered service in 1943, the target bearing and sub heading were automatically transmitted to the TVR. And it claims for the source of that information the hardware physically installed in U-995. The provenance of that hardware may or may not be verifiable. I assume that it is, and that U-995, being a military vessel, has reasonable maintenance records. But the vessel has been through several hands, so undocumented modifications might exist.

What is the source of the claim that WW2 vintage TVRs did not have automatic target bearing and sub course inputs?

[Rockin Robbins]

Ding! Ding! We have a weeeener! We have a weeener! I'll buy that for a dollar! The problem with a defeated nation is that we are often forced by lack of records to reverse engineer their capabilities. Sure would be interesting to know the history and development of their TVR, which was just as admirable a piece of engineering as the American TDC.

After all, it doesn't matter what hardware and software is used to create the music. It only matters if the final product rocks!

[BigWalleye]

Originally Posted by Rockin Robbins

Sure would be interesting to know the history and development of their TVR, which was just as admirable a piece of engineering as the American TDC.

Yes, it is interesting, and the tvre.org site provides quite a bit of that history and development background, going back to the first torpedo fire control systems developed to support the first "automobile torpedoes" (as they were styled). If you are actually interested in this topic, I think you would find the entire site worth reading. I can't vouch for the accuracy of the material. The site has extensive source attribution, but I haven't tried to cross-check those sources.

The tvre.org home page contains this "mission statement":

"The goal of the Torpedo Vorhaltrechner Project is to describe the development of the torpedo fire control systems used on submarines. The project evolved from an attempt to create a description of the German torpedo data computer that was manufactured by the Siemens Company and used on German U-Boats, known as a Torpedo Vorhaltrechner. Many incomplete and often inconsistent descriptions of this device can be found in books and on the Internet.

"During my research into this equipment I discovered the full scope of the torpedo fire control problem. For that reason, aside from a description of the German torpedo data computer, this project includes descriptions of similar American, British and Japanese devices as well as the history of the development of such systems - from the beginning of the torpedo weapon’s existence to modern times"

Unfortunately, I couldn't find the name of the site's author, so I can't give him proper credit. If anyone knows, please post it. He(she) has done a major piece of scholarly research.

EDIT: And I still hope that someone (TorpX?) will post a reference for the TVR description which indicates that it does not have automatic input for taget bearing and sub heading. Because this source is likely describing an earlier version of the TVR (pre-1941, when the S3 went into service), and it would be nice to have more information about those earlier versions. Anybody help?

[ColonelSandersLite]

Thanks for those links walleye. I'll definitely want to read them in detail later.

So far, I've read most of this page http://www.tvre.org/en/development-o...e-kriegsmarine and this http://tvre.org/en/torpedo-fire-cont...german-u-boats and noticed a couple of interesting things.

Re u-boats not automatically sending bearing to their tdc. I'm not 100% sure as I need to do more reading in detail, but I got the impression that what we're talking about here isn't actually directly related to the tdc, but rather the fire control systems it was connected to.

I.E. the TRW and T.Vh are separate but related topics.


It's off topic, but I also saw in the first link that prewar, the germans where firing spreads by turning the boat while firing. I want to try that soon, but to me that sounds absolutely horrible and I don't really see any logical reason to do it. Wouldn't it be easier and just as effective to use time for spread rather than an actual turn?