TDC, PK, manual targeting, corrections.

[Sniper297]

Playing around with CapnScurvy's OTC mod, set up my own mission so I already know what the target's actual speed and course are. Also playing with map contact updates on as "training wheels" so I can check the accuracy of my range observations and measure the true AOB.

Couple things about manual targeting, bearing is a no brainer and impossible to screw up, point the scope at the center of the target and there's the relative bearing. Range is more iffy even with OTC especially at longer ranges when you can't actually see the tops of the masts. AOB forever eludes me, difference between port 5 and port 10 takes an eye better than mine. Fortunately if I have the PK on it automatically tracks range - bearing - AOB and updates them with each new input.

One thing I'm missing, and a google search don't mention it one way or the other - what about speed calculations? If I have an exact range and bearing and take another perfect range and bearing X minutes and seconds after the first, I can run a course track between two points, and using the time it took for the target to get from point 1 to point 2, come up with a really close solution to the actual speed of advance.

TDC is an analog mechanical computer rather than the electronic digital gadget I'm typing this on, but if it didn't have a circuit to calculate speed automatically and correct it automatically based on each input - update it really should have. Theoretically I should be able to get a range and bearing, wait 5 minutes and input another range and bearing, the TDC should be able to figure out just from simple geometry and clock, using the difference between the two points and time elapsed, (1) target speed and (2) actual AOB. If it worked the way I think it should have worked, I should be able to leave speed and AOB at zero, input two range and bearing positions, and the TDC would give me something in the neighborhood of the actual speed and AOB without mussing its hair.

Anyone know the actual dope on the WWII TDC? Did the developers get this wrong and leave out some actual capabilities?

[TorpX]

Originally Posted by Sniper297

One thing I'm missing, and a google search don't mention it one way or the other - what about speed calculations? ....


Anyone know the actual dope on the WWII TDC? Did the developers get this wrong and leave out some actual capabilities?

Speed had to be manually input, just like the others.

There are probably a number of reasons why:

• 1. At the start of an approach, you would want to put in an initial guess. If you see a merchant chugging along, and see in the RM that it has a top speed of 12 kn., you might dial in 10 kn. and start with that.
  2. You might need to make a 'snap shot', and estimate speed based on bow wave or such.
  3. If the TDC rigidly calculated speed based on the last 2 positions entered, they could still be in error, if the target has zigged in the meantime.
  4. I think there had to be the option of the tracking party overriding simple calculations based on their experience.

Basically, the same goes for the Target Course/AoB. In theory these could be calculated if two consecutive positions were accurately known, but in practice, you need to estimate AoB and make manual inputs.

There were different models of TDC used in the war. I don't know all the details, but at least some were made so that as new data was dialed in, the error (or difference) between the observed data, and the TDC calculated value, could be seen. In this way successive observations could be used to refine the firing solution, and the crew could see the difference between the observed data, and calculated data get smaller and smaller.

I should also add, in the real-life TDC the PK was always 'on'. There was also a mechanism which showed the 'distance to track', but maybe not all models had that feature.

[Sniper297]

"You are asking your 40's vintage TDC to do some of the same functions"

I was born in 1953, so I'm also old enough to remember when electronic calculators were the latest high tech. I was an aviation ASW tech in the late 70s so I understand the technology of mechanical tracking systems, and the WWII TDC could easily have had the same functions.

Near as I can tell from the documentation though, that feature was not in the TDC;

http://archive.hnsa.org/doc/tdc/index.htm#toc

Because it was instead in the mechanical plotter, which SH4 doesn't even hint at. TorpX mentioned distance to the track, which near as I can tell was also incorporated into the mechanical plotter. Hard to find info on the plotter - I worked on the PT-396 plotter from the P-3 Orion and the ASA-13 plotter from the SH-3 Sea King, both were top secret at the time so finding details on those is also difficult. They were 60s technology but both were mechanical, with a tracer moved under a rolling sheet of translucent plastic burning lines and target marks on the underside.

Here's the only picture I can find of the WWII sub plotter table;



Under the sheet of glass you can just see the mechanical arm which is moved by small motors based on inputs from the TDC, gyrocompass, and pit log. At top just left of center you can also see the bottom of a repeater dial linked to the sonar console up in the conning tower, this gadget is down in the control room.

Game doesn't even hint at this technology let alone simulate it, the auto map contact update is probably the closest we'll ever get. What would be great is if some genius modder could reprogram the ingame map to display targeting and tracking based on input from the player instead of choosing either automatic full perfect tracing or no tracing at all.

[CCIP]

Yeah, from what I've seen and heard on the subs I visited, the TDC came with a tracking plot which was used for targeting solutions. I think in SH logic, it's not so much the TDC itself as the in-game attack map that replaces it, probably for gameplay reasons since it's a lot more intuitive than a linear plot, especially if you're playing with map contacts.

Interestingly, one of the subs I've been on where I was told about the paper plot was the USS Pampanito, and IIRC that was the sub that the SH4 devs visited when building the game, so I thought that the TDC was modeled on the one on Pampanito, except for the plot.

[TorpX]

Originally Posted by Sniper297

What would be great is if some genius modder could reprogram the ingame map to display targeting and tracking based on input from the player instead of choosing either automatic full perfect tracing or no tracing at all.

Agreed.



I don't believe subs had the full mechanical plotter as you describe it. I think there was a plot table with a dead reckoning indicator, that would show the position of the sub (not sure if all subs had this). It wouldn't be directly linked to TDC, but rather both the TDC and DRI would receive input from the pitometer log and gyro compass. The targets would have to be plotted by crew.

Furthermore, the TDC was developed before Radar. The 'normal' method of approach would be to close submerged, and make periodic observations, by periscope. This means the tracking party would have to figure out when and where the zigs occurred, and iron out any inconsistencies in the plot. The process could not be completely automated; they had to be able to make changes.



P.S.

I looked at some of the diagrams in N. Friedman's sub reference. He shows a few examples of the conning tower layouts. At it's last refit, Haddo had a Mk. 4 mod 0 TDC, and a DRT (dead reckoning tracer?) table in the back of the compartment. As they were close together, it is possible they did work together in some fashion. By war's end, the CT's were very crowded.

Early TDC models took up more space, and were located in the control room. Experience lead them to design a more compact unit to put in CT, so skipper could see both plot, and TDC data, and the TDC could get inputs from Sonar/Radar. I wish we had the nitty-gritty details on all this.

[Sniper297]

Off topic, but what in the world is with the pictures? I can post a picture by simply using CTRL-C to copy an image, then CTRL V to paste the pic directly into the post. But the pictures later mysteriously disappear, at first I thought it was imageshack, but pictures not hosted on imageshack are also MIA. So I started copying the URL and using the Insert Image button at the top instead. My second post in this thread (#5) had a picture of a plotter in it, now it's gone.

I'm looking over the FAQ and rules, I don't see anything except a restriction on posting X rated stuff. Is there an unwritten policy about image size, dimensions or kilobytes?

[Sailor Steve]

I'm not sure why you would be having picture problems. Other pictures on the forum are showing up fine, and no, there are no size restrictions I'm aware of.

I use PhotoBucket myself.

[Longknife]

I am not 100% I get what your asking so I will answer what I think you re asking

The TDC is a mechanical device. Think of it like an abacus. It's keeping track of the data inputted much as an abacus keeps track of the sums entered but also like an abacus it takes a cognitive element to interpolate the data.

I am old enough to remember when calculators hit the scene & they were a marvel of the 60's. You are asking your 40's vintage TDC to do some of the same functions.