how to re-set the tdc

[Joe S]

I had a great shot at a large merchant right in front of me at about 500 yds but for some reason the TDC was aimed at a target off my stern. I tried re-entering the bearing and range and even hit the button to shut the tdc off and start over but it would not re-set. two torpedoes were wasted. What is the fix or correct procedure? Thanks! Joe S

[Rockin Robbins]

Entering new data replaces the old. In order to switch to a new target you have to enter info in this order (the first two can be reversed without bad effects): speed of new target, AoB of new target, and last (that is important!) the range/bearing of the new target. It is not necessary to turn off the position keeper at all. Make sure you didn't forget anything by switching to the attack screen to ensure that your target is properly entered before you fire. Always verify that you have a good solution before firing, as the real boats also did.

If you do not have time for that, can you afford to waste a torpedo? If not, start over with a new setup. Patience, grasshopper!:hmm:

[Joe S]

Thanks for the help rockin robbins! I had the target locked in the scope when I re-set with the new bearing and aob,does it make any difference if the target is locked or not? Thanks! Joe S

[Powerthighs]

No, it doesn't make any difference. When you click the "send range" button the bearing the periscope is currently pointing to is sent as well. Having the target locked just makes sure the scope stays pointed at the middle of the ship whlie you move the mouse to click the button.

[Torpex752]

Make sure you didnt have a stern tube selected for a forward shot.

Frank

[Rockin Robbins]

No, the "is the lock necessary" question was the first step in my development of the Dick O'Kane (http://www.subsim.com/radioroom/showpost.php?p=652326&postcount=67) targeting technique, where I turn the @#$@# PK off, throw target range out the window, sight the TDC at a presently empty spot in the ocean and aim so accurately that I can hit 5 yards aft of the bow crane.

The periscope lock has nothing to do with targeting other than holding the periscope's crosshairs on the middle of the target. For conventional targeting this is a great thing because you're doing so much input all at once.

Also, the PK must be on to show the impact point on the target. With the PK off, you can see the torpedo track on the attack screen but not the impact point. With the Dick O'Kane you never see the "x" on the target and you won't miss it either.:arrgh!:

[Joe S]

I assume you got the Dick o'Kane method from one of his books, both of which I have read , but not recently. If you did get the method from his books, can you tell me which one and approx where so I can re-read that section?

You probably already know this but maybe some people do not: once you establish the amount of lead in degrees for a given target speed, that angle of lead is good no matter what the range. In the example you gave in the above referenced post, a lead of 9 deg was used based on the speed of the target. If you have an accurate target speed calculation, all you have to do is aim the torpedoes the given amount of degrees ahead of your desired point of impact and you should get hits.
I believe your method is sound, but have not tried it. After I try it I may have a few more questions. Thanks for your help. Joe S

[Munchausen]

When you use the stadimeter to insert range, you also insert bearing. The TDC then uses your crosshairs to determine the hit point (white "x" on the attack map when PK is engaged). If the target is locked, the crosshairs will be centered on the midsection of the ship ... but, if you take a stadimeter reading with the crosshairs centered fore or aft (no lock) then your computed hit point will also be fore or aft of the target's midsection.

[Rockin Robbins]

I assume you got the Dick o'Kane method from one of his books, both of which I have read , but not recently. If you did get the method from his books, can you tell me which one and approx where so I can re-read that section?

You probably already know this but maybe some people do not: once you establish the amount of lead in degrees for a given target speed, that angle of lead is good no matter what the range. In the example you gave in the above referenced post, a lead of 9 deg was used based on the speed of the target. If you have an accurate target speed calculation, all you have to do is aim the torpedoes the given amount of degrees ahead of your desired point of impact and you should get hits.
I believe your method is sound, but have not tried it. After I try it I may have a few more questions. Thanks for your help. Joe S
In his books, O'Kane tells how he dispenses with the necessity of knowing the precise range and turns off the position keeper during some attacks. With the help of aaronblood and gutted, we reasoned out that the most likely type of attack which met those characteristics was a modified Fast-90 attack from the U-Boats. Gutted had made a chart showing the lead angles for German torpedoes, which he modified for fast and slow Mark 14's.

For the fast-90 attack to work, you look up the lead angle for the target speed. First you set the torpedo to run up the zero bearing. Then you point the periscope at that angle before 0º, 360 minus the angle for targets moving left to right and the angle for targets moving right to left. As juicy parts of the ship cross the crosshairs, shoot.

Then it was left to me to figure out how to use the blasted thing. At the time we were all under the impression (the manual said so) that in order to work the stadimeter the periscope had to be locked on a target. This was bad. So I loaded up WernerSobe's Natural Sinking Mechanics test mission and went to work. After much trial and terror, I found that the periscope didn't have to be locked on anything to send a bearing. You didn't even have to use the stadimeter when you sent a bearing. You could set the torp track across empty water by pointing the periscope at a bearing and pressing the send range/bearing button. Then you sent a bearing without a range. Perfect!

So I set up for a fast-90 with gutted's chart. 9 knots = 11º, blah, blah, blah, shoot! And the torpedo passed well in front of the target. @#$@#$%@#$$!!!! I analyzed the attack and found that I had used the column for slow torpedoes on a fast torpedo. And I realized that you would have to have a separate column for Mark 18s and cuties and... This is so complicated nobody will be able to hit anything. What now?

There was only one option: find a way to toss gutted's chart. And then I realized that we already had a chart that picked its own column: the TDC! As long as the PK was off, all the TDC did was calculate the lead angle for a target moving at a certain speed for a selected torpedo. So the Dick O'Kane technique was born. No more chart!

Now, you measure the speed of the target and enter it into the TDC. Doesn't matter which direction it's moving in, you set that with the AoB. Now you set the AoB for 90º minus the number of degrees from zero you're going to shoot! If you're going to shoot at 350, your AoB will be 90 - 10 = 80º. Your target is moving left to right so your AoB will be starboard (right) 80º. Lastly we'll select a forward torpedo tube, point the periscope at 350º and press the send range/bearing button. OK, now maybe 15 minutes before you shoot we're all set up and all we have to do is wait. You can look all around with the scope and not mess up the shot.

OK, here comes the boat. You don't even have to keep the scope up, just look at the sonar bearing and take a peek now and then to make sure he hasn't changed course. You're a hole in the water here. When the sonar bearing gets to about 340, raise the scope and point it at 350. Open up a couple of tubes. As the front crane passes the crosshairs, shoot. Cycle to the second tube and shoot it as the aft crane is in the crosshairs. Two booms will follow and the ship goes down. You had the whole shot set up 15 minutes before the ship got there!

Is that as easy as it gets? I think so.:arrgh!:

[Joe S]

I was just about to post another message when I saw your recent post. In the course of trying this out, I discovered, I think, that you need to set the range to something in order for it to work, so I set it at 1500. First, of course, you set the target speed. Then set aob 90 left or right depending on the setup. Then set range to 1500. THEN, pick a target. Aim the scope where you want to hit, click the send bearing button and shoot. Move the scope a few degrees to the next spot on the target and shoot agian. Pick another target. Aim at a spot on the target, click the range button and shoot. Pick another spot on the target and shoot again. (too bad the game doesnt automatically select the next tube) so far, in my limited testing, you need to click the send range button for each target but not each shot. I havent tried it in an ideal setup, with two or three targets between 350 and 20 degrees and under 2500 yds but so far in the Borneo mission I have been getting hits on multiple targets, not 100%, but definately worth pursuing. Thanks! JOe S

[jazman]

It's funny, but I'm pretty bad at everything except for the O'Kane method. Somehow that method has "taken", I even figured out all the trigonometry.

I've tried with the PK all sorts of ways, and I just can't get range right. I hate the Stadimeter and all its works.

[Joe S]

Jazman,

forget about the range, it means nothing. The reason is, once you know the amount of lead, the angle of lead stays the same no matter what the range. I normally set the range with the rangefinder, but I use averages for the type of ship. for example, I enter 98 feet for the mastheight of all large freighters. Then I estimate the range with the split image, etc, but I do it mainly to replicate what the original captain or fire control officer did. Since most of my shooting is done under 1500 yds, I manually adjust the range once the target gets in close so that I get an accurate representation of the setup on the attack map to confirm the solution. If range is your main problem, you are in good shape. I hope you find this helpful. Joe S

[Rockin Robbins]

I've tried with the PK all sorts of ways, and I just can't get range right. I hate the Stadimeter and all its works.

Yes, hating the stadimeter is a healthy American thing to do.:up: I'll bet there was some cursing of the stadimeter going on aboard the real subs too.

[jazman]

Jazman,

forget about the range, it means nothing. The reason is, once you know the amount of lead, the angle of lead stays the same no matter what the range. I normally set the range with the rangefinder, but I use averages for the type of ship. for example, I enter 98 feet for the mastheight of all large freighters. Then I estimate the range with the split image, etc, but I do it mainly to replicate what the original captain or fire control officer did. Since most of my shooting is done under 1500 yds, I manually adjust the range once the target gets in close so that I get an accurate representation of the setup on the attack map to confirm the solution. If range is your main problem, you are in good shape. I hope you find this helpful. Joe S
Thanks for the advice, I have the O'Kane method down cold. And I worked the trigonometry so I understand why the range doesn't matter. It's when I use the PK for non-O'Kane shooting that I have problems with range.

[Joe S]

Jazman:

Range doesn't matter with either method. If you want, you can pre-set the range for the distance to the target's track at the point of firing. If you are off by a little or a lot it makes no difference. Test the theory in the training mission and let me know what you find. Joe

[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]

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]

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]

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 (http://www.subsim.com/radioroom/forumdisplay.php?f=225). 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:damn:) 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.