how to re-set the tdc

[Joe S]

Jazman,

If you are having problems with manual tdc it is NOT because of the range estimation. It is more likely error in the speed estimation. a small error in speed estimation will result in a miss except at extemely close range. If you want to improve the stadimeter range finding method, determine the height of the smokestack, which is easier to see than the top of the mast. The top of the mast often dissappears making it impossible to get an accurate fix. If you use the smokestack heigh you should see a big improvement. Joe

[jazman]

Originally Posted by Joe S

Jazman,

If you are having problems with manual tdc it is NOT because of the range estimation. It is more likely error in the speed estimation. a small error in speed estimation will result in a miss except at extemely close range. If you want to improve the stadimeter range finding method, determine the height of the smokestack, which is easier to see than the top of the mast. The top of the mast often dissappears making it impossible to get an accurate fix. If you use the smokestack heigh you should see a big improvement. Joe

OK, I spent some time working out the trig on a non-90 AoB solution. If we know the AOB, and the target speed, and the torpedo speed, and the range, there are two unknowns to solve: the time of the run, and the gyro angle. We need two equations. The ones that come to mind are the law of sines and the law of cosines. The law of cosines, unfortunately, seems to depend on the range. If the range is an unknown we're hosed because we need a third equation, am I missing something? Surely there are computational methods to solving this? That would be why you need a _computer_, right?

For the 90-deg AoB, the time of the run is an unknown, but cancels out nicely, and you need only one equation, because only the gyro angle is unknown. A basic trig equation works.

[Joe S]

Jazman,

I had a rough time with high school algebra. All I can say is that range is the least important component of a firing solution, no matter what method you are using(with some exceptions that probably dont apply here.). At any rate, on the nav map, draw a line representing the target's course. Pick a spot that marks the approximate location of the target where you plan on torpedoing it. Measure the range from that spot on the target track to your sub and enter it manually into the TDc. If you have an accurate speed estimate and your range is under 1500 yds you should be getting hits. I hope this helps. Someone with better math skills than me is going to have to explain the mathematical reason why range is not important. Joe

[jazman]

Originally Posted by Joe S

Jazman,

I had a rough time with high school algebra. All I can say is that range is the least important component of a firing solution, no matter what method you are using(with some exceptions that probably dont apply here.). At any rate, on the nav map, draw a line representing the target's course. Pick a spot that marks the approximate location of the target where you plan on torpedoing it. Measure the range from that spot on the target track to your sub and enter it manually into the TDc. If you have an accurate speed estimate and your range is under 1500 yds you should be getting hits. I hope this helps. Someone with better math skills than me is going to have to explain the mathematical reason why range is not important. Joe

It's probably that in the exact mathematics it matters, but for practical purposes (here come the engineers!) it's a wash. I guess all the focus on range is because the lower the range, the greater the margin of error and still get hits.

[XLjedi]

Hmmm... The "O'Kane Method"

For those interested, my nod to O'Kane's tactics were sourced from the war patrols of the Wahoo and Tang books that O'Kane wrote. I think the Wahoo book goes into a little more detail on the firing methods he developed as an XO under Morton.

The one thing he wrote about that stood out in my mind did, in fact, involve overriding the PK. He ordered that a certain targetted bearing be held constant and then he would fire torpedos as points of interest passed the stationary aiming wire. I could quote the chapters and paragraphs but I'd have to go checkout those books again from the library.

However, I do not recall O'Kane EVER writing anything about range not being of importance. I think Robbins memory there is more likely being influenced based on my commentaries on zero-gyro angle shots.

Actually, I don't really care for (at all) the use of a table of lead angles in place of the TDC. To me that just seems silly. ...and to mention it in conjunction with O'Kane probably borders on insulting. The guy was clearly a TDC/PK wiz, and he used the device to its greatest effect. I do not recall O'Kane (in either book) ever referring to a degree lead table as he called his shots.

To the contrary, O'Kane wrote that he drilled continually, both himself and his crew, using a little ship on a Lazy-Susan to get better at estimating AoB. His practice of trying to limit observations to just a few seconds also suggests that he was relying on the PK and other devices to carefully track his prey.

I proposed to mimic SH3 Fast-90 tactics in SH4 in the second "O'Kane Tactics" link of the following thread (and there's a third link there to Robbins followup tutorial). I just liked the idea of giving O'Kane the nod for instilling in me the idea that US sub skippers could override the PK. When I read about that I thought, "Hmmm... Be neat if I could mimic that in SH4."

http://www.subsim.com/radioroom/showthread.php?t=121929

I am pleased at least to see that O'Kane's name has stuck to the tactics described as it pays respect to a great American hero. However, it is starting to get a little too watered down in its presentation and anyone claiming to have "developed it" perhaps comes across as a little boastful. Fast-90 by it's very nature was a method to calibrate the TDC, didn't have anything to do with a lead degree table.

...all I was doing was reapplying what I originally picked up from Wazoo's manual on Fast-90 for SH3. So I wouldn't even go so far as to say that "I develped" or came up with anything special. My original suggestions for applying Fast-90 principles to SH4 did seem to mimic O'Kane to a degree (holding the bearing constant and firing as points passed the wire) so I think he rightly deserved a nod.

Also worth noting that I don't recall ever reading a book on German Uboat tactics that actually used the term "Fast-90", I believe the first and only time I ever saw that term used was in Wazoo's SH3 Manual Targeting Booklet and perhaps scattered here on the SH3 message boards. Someone correct me if you know of a valid historical reference (in fact, I'd love to read the book if it exists).

[XLjedi]

Originally Posted by jazman

It's probably that in the exact mathematics it matters, but for practical purposes (here come the engineers!) it's a wash. I guess all the focus on range is because the lower the range, the greater the margin of error and still get hits.

Well... not an engineer... but here comes the finance/programmer guy.

If target speed and course are constant, and intercept speed and course are constant, there's a trig solution that gives the third side of the triangle and thus calculate the intercept course. The three angles of the triangle never change as the torpedo approaches its target. The bearing to the target remains constant (you may have heard of the Constant Bearing Formula?) right up until impact. Since this solution never changes as the two objects converge you could infinitely expand the distance between the two and still score hits on a perfect 2D plane.

Likewise if you're running the bridge of a ship and you have a radar bearing on another ship and you notice that as you track that ship for 30 mins the range is steadily decreasing but the bearing is not changing what might that be telling you? (you're on a collision course)

There is one variable that does throw a wrench into the sub targeting though. The torpedo advance. The range doesn't matter commentaries relate only to low gyro angle shots. If you are shooting with more than a 3-5° gyro then your solution will be influenced by error in range estimation. If you typically shoot within the 1000-2000 meter range then set the TDC for 1500 and you don't have to worry too much about it if you keep your angles low.

Incidentally, I always thought it would be cool to drive a train. Then people could ask me what I do and I'd say, "I'm an Engineer"... and they'd say something like, "Oh, really? Mechanical or Electrical?" and I'd say, "Trains".

[Rockin Robbins]

Actually there was no name for the technique while we were playing with the blasted chart. Like aaronblood, I considered the chart to be cumbersome. After we developed using the TDC with the PK off, aaronblood called my attention to the fact that Dick O'Kane had mentioned doing that without actually detailing the precise method he used. Because Morton and O'Kane were renowned for being the preeminent TDC wizards, and we were using the TDC in a non-standard way, aaronblood suggested that we name the method after O'Kane, as a tribute to that great man. I never meant to imply that Dick O'Kane ever used the exact method, but he certainly used elements of it.

Aaronblood is a spreadsheet jockey extraordinaire and knows his trig like you know the alphabet. It was he, after I was feeling all puffed up about writing the tutorial on the Dick O'Kane method (I offered him and gutted first shot and got stuck writing it), PM'd me with the news that I blew the attack. Without aaronblood there would be no Dick O'Kane method in SUBSIM. I have a big mouth, he has a big brain. He called my attention to the fact that I had the AoB wrong and the only reason I hit the target was that my solution and the correct solution happened to overlap.

He sent me a cute little MoBo plot to prove it, too! If you really want to understand what is happening in the TDC and want to understand the mechanics and analysis of the attack in detail, you HAVE to try out aaronblood's MoBo, found on SUBSIM in its own section. I'll bet everyone has wondered what the MoBo logo on my siggy is about. Well, there's your link and I can't recommend it highly enough.

In an unrelated aside, in SH4 the TDC automatically adjusts for whatever torpedo you select. In real life, the TDC was set for a single torpedo speed, or maybe just the two speeds of the Mark 14. I just read an account of a layover of a sub (can't remember where I read it or what sub it was) where when being equipped with their first Mark 18's the TDC had its gearing overhauled for the lower torpedo speed. This implies that mixed loads of Mark 18 and Mark 14/23 wouldn't have been a great idea. In the game it's no problem! But the TDC was a mechanical analog computer, full of shafts and gears.

[jazman]

Now I'm looking at this MoBo thing. I've just downloaded and am reading the documentation. What a nice little piece of work, now I can put the OOD to work instead of him just gaping at the nav map.