Quote:
Originally Posted by Urge
You can lay out a 45° attack plot on the map but when you zoom in all the way it may be off by a degree or even 2 that is not obvious at lower zoom levels.


Munchausen wrote...
I am referring to zooming in on the nav map. Sorry if that wasn't clear, it made perfect sense in my head but I guess it didn't translate well.

Urge

I have cleared the deck
 

I have cleared the deck and I am going to hunt ships and use the Cromwell attack technique, with the lead angle determined per Old Tex's chart re Cromwell Method of Torpedo Attack, and I WILL NOT INPUT THE TARGET'S SPEED IN THE STADIMETER. I will report back after the mission. Take her down.

My next assignment is the Radio Mod.

I think this is where you are going wrong. The AoB that you enter is the AoB of the ship currently. The 45 degree intersection means that at the point of impact the target's Aob will be 45 degrees to port or starboard. What I think you are doing is telling the TDC that the target already has a 45 degree AoB at the shooting bearing. This will make the TDC think that the target has a different course, which takes the target further away from you, so it tries to compensate by making the torpedo head a bit to the left or right to compensate.

To properly get the AoB, you need to calculate the angle between your line of sight to the ship. If you want to use the TDC to verify your shooting calculation, this means that you will need to enter the information as it will be when the target crosses the wire. That mean you need to measure the angle between your line of sight and the target's course on your drawing. That is the target's AoB at the time to shoot. You then put this info in, at the shooting bearing, with teh target's speed and it should give you a zero gyro angle shot.

If you are going to use the TDC in such a way though, it's no longer a simple drawing method and you are starting to use the TDC the way it is meant to be used, except with the PK on and then you are fully manual targetting. And then you can use spreads, which are a much better way to shoot torpedoes, spreading from aft to bow you'll get a whole lot more bang for your buck. You're only a step away :D. Keep going. I admire your perseverance!

That's a good tip, gives you a bit more accuracy.

Nisgeis has hit on half of it. The AoB is VERY important here. Use the rule: 45º minus the lead angle.

And the rule of thumb for a 10 knot target (or anything close to that). Out of the air, produce a 10º lead angle. For a target moving from right to left, your shoot bearing should be 10º then, not zero as you shot. I don't get excited about anything less than a 10º gyro angle, even at extreme range.

With this example, you would set the TDC for speed: 10 knots or whatever the target is going. Set AoB at 45-10=35º port. Now the torpedo will go up the approx zero degree bearing to hit the ship. You're shooting at 10º. When he gets to zero, there will be a surprise waiting for him. I hope he's happy with his Christmas present.:yep:

As Tim Tebow, you are throwing the ball not to where the receiver is, but where he will be when the ball arrives. Did I just lose three-quarters of the world or what?http://i196.photobucket.com/albums/a..._greenguys.gif

Hmm?
 

No news yet. I tried two attacks on task forces. I did not input the target's speed on the first attack, but I did input it on the second one. I will stick with the second alternative for now, as not entering the target's speed may have been a bad idea.

The first attack. I set up too late, so I decided to try a reverse Cromwell attack, firing at a carrier at a 45 degree angle as the task force was pulling away rather than closing. A destroyer got in the way and absorbed two of the four torpedoes, and the other two missed.

The second attack. Again I set up too late. Again, I set up for a reverse Cromwell attack as the task force pulled away. My sub was detected, rammed, and depth charged. I fired four torpedoes at a carrier at the requisite lead angle. I had previously set the speed and range, but I did reset the AOB. All four shots missed. I checked the Attack Map. While reseting the AOB to deal with the fact that that target was pulling away, the task force, including the target, had turned 60 - 70 degrees to port (away from my sub), and were almost parallel to my boat, presenting minimal target aspects. The shots missed, but not by much, which was a pleasant surprise. The course shift by the target likely accounted for the misses.

I have saved the second attack a point where I was closing for the shots, so I can replay the attack and see if I can avoid detection and get properly set up for the Cromwell attack or if necessary, for what I call the reverse Cromwell attack.

:hmm: Perpendicular? Wouldn't that present the maximum target aspect?

Perpendicular was a mistake which I corrected.
 

Darn, your mama taught you how to read.

I saw parallel in my head but I typed perpendicular. I just corrected the post. And next time I will try to sneak something past you....

First things first: Thanks for the method Nisgeis and thanks for the tutorial Rockin Robbins (hope I got the credentials right)

The most helpful to me in the tutorial was the part about the vector solution on the NavMap. It was helpful to the point of me forgetting about approaching at certain angles and just measuring the given situation as well as forgetting about any TDC Input. At best I identify the target for getting torpedoes running depths.
If this is just my method to avoid "driving like a drunken sailor" or if I'm just to drunk to drive at all, that's a different topic.;)

I'm thinking that it could be helpful to reference the explanation behind the vector solution and its demonstration in the stickied tutorial thread, since Dick O'Kane and John P. Cromwell are the two extreme cases of the same solution.
Having it covered here under 4 pages of questions and ty's might not be ideal.

Yes you did. Initially RR didn't want to include the vector analysis as part of the tutorial, but thankfully I managed to talk him round. If you're drawing the vector analysis, you're only a short step away from using the TDC for any situation that might come up.

As posted previously, I had saved an attack on a task force, so I could replay it until I set it up correctly for an attack using the Cromwell attack technique. I kept screwing up the set-up until I replayed it today for the 5th time. I fired four shots at a carrier at 3300 yds with a AOB of 45 degrees. It wa or 6th time. The task force course was to closing on my port side I set my lead angle at 352 degrees. The carrier was travelling at 11.5 kts. and I was using 46 kt. torpedoes. According to Old Tex's chart the AOB should have be between 351 and 352 degrees. I fired the first two torpedoes towards the carrier's bow, and the last two towards its stern. The first two hit amidships and the last two hit near its stern. I noticed the gyroangle was not at 0 degrees. My ship was dead in the water when I fired (that is how I know the distance to the target was 3300 yds.), and there was a gyroangle showing on the Attack Map at +1 or +2 degrees (I did not have time to look to see the precise degree of the gyroangle.) Assuming the TDC somehow computes a slight gyroangle (even though the PK is not turned on), with my crosshairs pointed at 352 degrees when I record the range to the Stadimeter, should I adjust the setting of the crosshairs for purposes pulling the trigger on the torpedoes (not for purposes of resetting the range on the Stadimeter) because the gyroangle is not 0 degrees, or should I calculate lead angle by starting at +1 or +2 degrees and send the range to the Stadimeter based upon the new periscope readingr? The purpose resetting the crosshairs is to compensate for the fact that the gyroangle is not at a 0 degree bearing. If that is the correct thing to do, I shoulld adjusted the crosshairs to a bearing of 353 or 354 degrees undler the assumption that the correct gyroangle of -8 degrees calcuated from the gyroangle of 1 or 2 degrees rather than 0 degrees.

Secondly, I set up this attack well ahead of the task force, and I used Silent Running with a speed of 3 kts. And then I stopped the sub. I fired my torpedoes and shortly after. Then my sub was picked up by destroyers and sunk. Usually they find my sub before I fire. Can they locate subs that use silent running or that are dead in the water? What's the deal?

The four shots that hit the carrier were set at 25 feet. They passed under an escort that was guarding it starboard side. The carrier sunk, and I saw it go down. Unfortunately, I missed most of its death throes because its view was blocked by the escort and my camera did not trigger because it went down slowly. Too bad. It is the first time I sank a carrier. During all the commotion, it turned out that a destroyer caught fire, but I am not sure how that happened. Maybe one of the torpedoes hit it, but that is unlikely because they were set to run deep.

At the impact point at 45 degrees, the target's AOB at the time of firing will be 180 - (135 + number of degrees from zero your shooting point is). So, if your firing bearing is 352, and the target's course will intersect yours at at the 45 degrees, then the target's AOB (which you put in the TDC) is 180 - (135 + 8) = 37 degrees to starboard.

It's 180 because there are 180 degrees inside a triangle, so if you know two angles (the intersection of both of your courses is 135 degrees (90 plus 45) and the angle you are looking at is the second angle, then the angle between the target ship's course and your line of sight is the remainder and that's the AOB.

You can also measure this from the map, but it's easy just to calculate out the 180 - 135 part as that's a constant and just use 45 - offset angle to work out the AOB. Putting in an AOB of 45 will make the TDC thing the target is on the wrong course and will give them a slight left gyro angle order to compensate.

I wouldn't recommend adjusting your fiirng bearing to make the gyro angle order become zero, you'll just be making innacurate data worse.

I'm going down, I think you're confusing terms and getting confusicated there. If you are then lots of people are and we need a new tutorial that is beyond my present means to produce. I could, however, make some diagrams defining all the terms.

I say this because I know you didn't mean Angle on the Bow when you said that in your last post. And that explained a lot of the problems you've been having. I'm going to have to play with some new drawing programs because Corel Draw 4 doesn't like Windows XP, so it will take a little time, but I'll get it done.

@Angron: you have it precisely correct, even more than you know. Nisgeis first came to me with an idea for an attack from 45º ahead of the target. First we talked about the possible reasoning to attack from that angle and agreed that there were two really big advantages and a third pretty good idea:

• when you are 45º ahead, you could actually shoot from ahead of the escorts
• while the torpedo is on the way to the target, they are approaching each other, actually making the shot more accurate because the angular size of the target is increasing as it approaches the submarine.
• a long distance shot is then more accurate and the target has less time to react because the closing speed is 70% of the target speed plus the 46 knot speed of a high speed torpedo.

After we agreed on the possible advantages, I got pretty excited and proceeded to work out the procedure according to my formula: no outside tools, simple rules of thumb, no calculations you can't do in your head, extreme simplification in everything.

And he picked out the name. He liked the idea started in Dick O'Kane of naming techniques after prominent submarine captains. We narrowed our choices to two and he picked John P Cromwell, as a captain earning the Medal of Honor for his personal sacrifice, not his skill as a top producer. Captain Cromwell chose to die rather than risk giving away the secret plans he knew of a coming invasion.

Then we had a train wreck. After I explained the procedure I would put into the video (quite proud of myself there, you can imagine), he came back with "but that's not what I think of when I think of the John P Cromwell Technique at all." He told me about the vector method of making sure you have a perfect zero gyro every shot. I regurgitated all my usual bull about my tutorials being for beginners with the motto that if my cat can't hit the target the tutorial is no good.

He said, "Try it, you'll like it." So I tried it. And I liked it. So I produced the video with a complete illustration of the vector analysis method along with my "rule of thumb" method along side. Which all begs the question "what next?" Gutted is out there thinking "I tried to tell you that a year ago!" But I was pretty single minded then about making tutorial for beginners and wasn't looking beyond that point. Now we can use the vector analysis method to take skippers beyond the beginning.

Because with vector analysis, range doesn't matter, no matter how long the shot, or from what angle. Any time you shoot with a zero (or in practice, a near zero of +-15º or so) gyro angle, you hit your target even if your range calculation is way off. You're not even entering range into your TDC.

So to answer your question, the original idea is Nisgeis', the name is Nisgeis', the vector analysis is Nisgeis', the rule of thumb method is mine, the tutorial is mine. The score: Nisgeis 3, Rockin Robbins 2.

My mistake
 

I made a mistake in communicating. The AOB was set to 37 degrees, not 45○. My apologies to Rockin Robbins, who first caught the mistake.

I read Nisgeis' last post. I understand how the 135○ angle is derived, although it took me awhile to conceptualize it. And I undertand that the AOB is calculated after the lead angle is input (in my example the lead angle was 8○) into the vector analysis,. Thus, the AOB in my attack on the carrier was 37○ [180○ (representing the number of degrees in a triangle) - 135○ (90○ + 45○)[representing the angle of intersection between the carrier and the torpedoes when attacking at a 45○ angle] - 8○ [represnting the lead angle per Old Tex's chart, or alternatively, calculated using the mehtod described in RR's tutorial]).

Having said all of that, it still does not account for the slight gyroangle on the Attack Map. If the slight gyroangle will not cause the torpedoes to miss, I will ignore it. However, if it will generate missed shots, then I want to compensate for it, even if it means adjsuting the firing point by one or two degrees. The problem is not in the calculations, it is in the gyroangle that the TDC generates on the Attack Map, since the torpedoes follow the gyroangle and not a 0○ bearing.

Assuming I am with you guys on an intellectual level re the vector analysis method of pinpointing the firing point, AOB, etc., I am trying to focus on the gyroangle issue created when the gyroangle is not 0○. It may be a non issue and if it is, fine with me.

Errors in gyro angle can be caused by slight errors in data dialed and sent to the TDC:

• Target speed
• AOB
• Bearing (periscope adjustment)

Even if you measured a dead-on accurate speed for your target, the speed dialed into the wheel might be off by a tenth of a knot. You could be off half a degree in dialing in AOB ... and the same for adjusting your periscope before taking a bearing.

All of that can add up (:hmm: I think RR said all this before ... but buried it in the middle of one of his longer explanations).

The TDC takes into consideration other issues for firing a torpedo, other than just solving the attack triangle. This is based on the real TDC, but it seems that the simulated one takes at least some of these into consideration. I'm not sure how exactly the torpedos are modeled in sh3 or 4. There is a time for the torpedos to reach their cruising speed, turn radius is different depending on which way the gyro is set, depth can play a part too, etc.

http://hnsa.org/doc/tdc/tdc01.pdf

This section of the TDC manual talks about the problems it solves. The gyro angle is set depending on distance to the target and its speed, and takes into account torpedo reach (before it starts turning via the gyro), and the turn radius.

So there shouldn't be too much concern when using the TDC compared to the simple vector analysis 'hip' shot. The TDC can be more accurate, but its not as important for near 0 gyro shots.

The mark 8 angle solver (banjo) does the same thing, but it uses a plate that the solver arm rests on to show the proper gyro angle. There is a different plate for each torpedo type, and the speed that the torpedo is fired at. I havn't been able to find a good picture of these plates.

I don't know if these factors are responsible for the slight error that is seen, but its something to think about.

I am now satisfied
 

Munchausen's post and Starbird's to a lesser degree have convinced me that slight errors inputing date create the gyro angle that is off by a degree or two. I can live with that. I just could not figure out the reason why it was not a perfect 0 degrees, and now I believe the reason has been explained. Thanks for putting up with my persistence.

Ordered to patrol the Bismark Sea west of Rabaul in Jine 1942, I and the rest of teh crew of the S-42 head north out of Brisbane. I decide to be aggressive and transit the narrow channel between New Britain and New Ireland in darkness, rather than burn precious fuel by running all the way west of New Britain and then back east to my patrol area.

As dawn breaks we clear the north entrance and I prepare to order a turn west, we first dive for a routine check of the hydrophones. Contact! She's far off in the distance, but a half hour of taking bearings tells me I should have a shot at an approach. I pop up to scope depth and finally make her out. Damn, she's a big modern tanker and she's hauling ass into Rabaul, but I should still be able to get a shot. Make the turn to intercept and a few minutes later realize to my dismay that she has turned herself to make her final run into port. I recompute and figure out my only shot will be a prayer. I decide to let her go.

Not a good start to the day.

The day wears on as we head east to what I've decided will be the fishing hole. Routine sound checks pick up a few long range contacts, but the plots indicate we have no real chance at catching them. Just as I'm about to surface after the latest disappointment, I sweep one more time with the hyrophones and pick up another very faint contact, 20 degrees off the starboard bow. One humdred fifty feet down, doing 2 knots, we turn right at her and listen. It's 1734 hours.

Five minutes pass. No bearing change, still very faint. Ten minutes pass, still no change. Twenty minutes pass, and finally a one degree bearing change. But she's getting louder with every reading, and she's coming right at me, course 075. This should be like taking candy from a baby. I'll just turn and glide in at 1 knot, putting a few in her side as she passes using the good old O'Kane method.

She keeps on coming doing 11 knots. She s a big old split merchant, 8000 tons worth, and I know where she'll be before she does. I listen to the gramophone like Lecter waiting for Deputy Pembry. At around 4000 yards, she slows, then accellerates. Damn it, another one is going to turn and get away. For a few seconds I panic, but I realize that I'm still OK, at least to try to chase her down. She's turned to the southeast, but having set myself up for a 110 degree shot, I speed up and turn to lag her just a bit, hoping to get myself in position for a new shot. If I want to have any chance at all iIve just got to steam along this line and hope I can figure out when and where to shoot.

A couple of visual readings and a few by sonar and I've got her pegged again. But how am I going to hit her?

Suddenly, I remember overhearing a conversation in the officers club in Brisbane. A couple of the old salts were discussing something they called the Cromwell method. I yell to the plotting team: "We're going to do some vector math!" 36 knot torpedo. 11 knot target. Maybe these drawing tools are useful after all.

She's steaming away from me, and I won't have as nice an attack angle as I want with an AOB of about 150, but the math says that if I lead her by 6 degress, I should hit. She's over 2200 yards out, 25 degrees off my starboard bow, and her lead is growing. I slow down one more time to minimize my scope wake. Up scope! I point the scope to 324, press the bearing input, then turn her back to 330 and wait. Her bow crosses the wire. I wait a beat. Fire One! Fire Two! A couple more beats. Fire Three! Down scope. With a 30 degree gyro angle I probably should have thrown in a "Hail Mary" with each fire command, but at this AOB and at her speed I barely had enough time to fire fast enough as she crossed the wire.

I hold Four in reserve, lying to myself that I'll need it for a coup de grace. If this doesn't work, I'm gonna give those guys in Brisbane the business. If I make it back to Brisbane, that is.

The torpedo run seems like it's taking forever. I know I missed. It's just taking too long and I'm too juiced up to find the wiz-wheel and figure the run time. It doesn't help that I did all my training with those new fast running fish and I'm stuck here hunting Japs with these 36 knot antiques. I raise the scope to watch a juicy target sail off into the fog.

The scope breaks the surface just as the sound man rings out: Torpedo Impact! All I see is a big splash. Then again: Torpedo Impact! Then a couple more beats. Torpedo Impact!

Holy cow! I think I owe those guys in Brisbane a beer.

*************************

It's was all so simple, I'm just wondering why I never thought of it before. Just one of those moments where you remember why you play the game.

Yeah, the above is NOT a "classic" Cromwell attack as outlined here, as I was most certainly NOT a zero gyro shot. But the basis for what I did grew out of the basic Cromwell idea, then I just did some quick drawing and figuring to make it work in a situation where getting in position for a zero gyro shot was not feasible because I wasn't smart and fast enough to get there. It all comes down to the vector analysis, and having good numbers on your target.

I never turned the TDC on in this run up, as I was setting up for an O'kane type attack and with frakkin' lock thingie wouldn't work for me so I had no target input in the bucket of bolts anyway. But once I knew where the target was going, the vector analysis works like a charm even for bigger gyro angle shots. You just have to hope the fish cooperate.

And yes, for close readers of the above, I screwed up port and starboard. But it's late and I was in Mickey Spillan mode. So shoot me.

Anyway, the cool thing about this game is figuring out new ways to skin a cat, then catching hell for waking up your wife because you're yelling like a schoolboy when your plan all comes together.

:up: Vector analysis opens up a whole new ball game ... bring on WWI!