Constant Bearing Method, with TDC

[I'm goin' down]

that explanation was too confusing for me to follow. Rockin Robbins provided a simple explanation. see posts 41 & 42.


I reread your post. I am guessing that what you attempted to descrbe is exactly what Rockin Robbins stated. If it isn't, I have no clue. By way of example, which direction is the nose facing. I think you are saying that the "nose" is facing the direction of the boat's true course? This is technical stuff, so please try to be precise.

[Rockin Robbins]

Originally Posted by gutted

you as captain should have a large bag of tricks. just try not to hemm yourself into 1 way of doing things.

A man after my own heart!!!! Gutted started my quest for collecting my "bag of tricks." His encouragement when I was a rather confused fleet boat skipper wondering if there were any tricks I could learn from the U-Boat people started the whole Bag of Tricks thread and is directly responsible for the Dick O'Kane technique and indirectly responsible for all the other constant bearing techniques and wrinkles I have developed.

Gutted sent me a very simple animated gif that began all the madness, along with his lead angle chart he's talked about.




And there you see the genesis of the Dick O'Kane technique, posted and sent to me 8/19/2007 by gutted. At the time he was strictly a U-Boat jockey who had spent limited time in a fleet boat. He jumped into a thread where an upstart called Cali03boss was stinkin' it up and with one post started a revolution in Silent Hunter 4. (In the formula above, it should say arctangent instead of inverse_tangent, but there's the key to the universe, right there!)

[Rip]

Originally Posted by Rockin Robbins

A man after my own heart!!!! Gutted started my quest for collecting my "bag of tricks." His encouragement when I was a rather confused fleet boat skipper wondering if there were any tricks I could learn from the U-Boat people started the whole Bag of Tricks thread and is directly responsible for the Dick O'Kane technique and indirectly responsible for all the other constant bearing techniques and wrinkles I have developed.

Gutted sent me a very simple animated gif that began all the madness, along with his lead angle chart he's talked about.




And there you see the genesis of the Dick O'Kane technique, posted and sent to me 8/19/2007 by gutted. At the time he was strictly a U-Boat jockey who had spent limited time in a fleet boat. He jumped into a thread where an upstart called Cali03boss was stinkin' it up and with one post started a revolution in Silent Hunter 4. (In the formula above, it should say arctangent instead of inverse_tangent, but there's the key to the universe, right there!)

This discussion and the fact I am currently reading Wahoo written by the Rear Admiral has me pondering this. At least when O'kane is XO he and Mush normally were shooting 120 AOB shots. Should I be? You would need a different chart for that I would expect? IIRC he wrote that made it harder to maneuver away from the shot.

Now I also wonder if he kept doing that after getting his own command or did he start going for 90 shots?

[Rockin Robbins]

I dunno. I think he took the shots as the situation dictated and wrested the odds as best he could. It's not like you look at an unfavorable position and say, "Nope. I don't like that angle."

Statistical analysis shows that a torpedo track angle of roughly 110º (varies with speed) is the most tolerant with regard to errors in calculating target speed. Reverse analysis of their mumbo-jumbo showed that firing at AoB 90 or slightly afterward was best for that.

As far as maneuvering out of the way of the torpedo, a torpedo track angle of 90º would be the best because the target has to turn just as far in both directions to avoid.

Let's reason this out. You're firing a John P Cromwell attack from 45º ahead. That ends up giving you an AoB of about 35º starboard or port depending on which direction he's coming from. The sharpest he has to turn to get his bow toward the torpedo and then be able to turn left or right to avoid is.....45º, right?

OK, let's take the O'Kane situation. The torpedo approaches from 30º or more aft of the target beam (torpedo track angle of 120º or slightly more). We'll assume the target is moving left to right. Since the torpedo is approaching from aft, the speed of the target makes the approach speed of the torpedo slower, giving the target more time to react. Then the target needs only to turn 60º to port, hit the throttle and maneuver left or right to let the torpedo, now on a parallel course, pass starboard or port.

I don't understand O'Kane's reasoning there. I'd rather be firing from ahead of the target if I can't pick the 90º attack, so that I have lots of wiggle room in my calculations and can absorb maximum error. Failing that I want the target to have minimum time to react if he sees the torpedo.

[Frederf]

I wonder if there's some factors that we're leaving out. There are a lot of assumptions about a target maneuvering to get out of the way of a torpedo.

1. Target spots the torpedo equally well in all directions.
2. Target is able to ascertain torpedo motion well enough to make a fully reasoned maneuver.
3. Target decides what maneuver to make on a case-by-case basis instead of some rapid and wrote drills.
4. Likelihood of torpedo hit overrides all other tactical considerations like defensive posture.

If all Japanese merchants were known to be trained to turn left when under a torpedo attack then that certainly changes your tactics. One might also regard that a target passing through AOB 90 gives the best chance to take good speed, course, etc data for an accurate shot which leaves the submarine aft of beam since the torpedo launch comes after the data taking.

@RR: I'd like to see the same animated .gif with 1 torpedo passing through all 4 targets as if they had a hole in the middle of the ship. That picture is one way I like to attack convoys as several targets' solutions converge.

I have found the AOB150 shots to be more error prone but then again I'm behind a desk and not in a leaky iron warboat 2000mi from home.

As for Cromwell v OKane... they both give about the same leniency to the target to turn a short angle to negate the solution, apart from the time-to-impact difference. I think TTa 90 gives the most difficult evasion scenario for the target but I'm not 100% sure.

Also ArcTan, Inverse Tangent, or Tan^-1 are all perfectly acceptable synonyms. I prefer the Tan^-1 notation when I can actually write the superscript proper unlike in forum posts. I kinda consider the "arc" prefix to be rather anachronistic and to be dropped from high school textbooks steadily.

That chart has an error of either language or trig function. If you want to fire such that the torpedo tracks squarely into the target's side then that isn't a 90 AoB shot but a 90 TTa shot in which case ArcTan is correct. If you want to fire when the target is at 90 AoB (TTa > 90) then ArcSin is correct.

[gutted]

I called it 90AOB on my table due to the fact that in the U-baot (re: SH3) the periscope and aob dials were linked. so to take this kind of shot all one had to do was put the scope at 0 degrees.. set 90AOB (or any AOB for that matter), then train the scope left or right until the gyro read 0. thus taking a 90AOB shot. though techincally, it was less than 90AOB at the aim point becaues the AOB would change autommically with the scope in SH3.

this table was my attempt to simplify this for SHIV, since the two dials were not linked as in SH3.

As for arctan, invtan.. im no mathemetician, but aren't they are the same thing. i put inverse tangent because the windows calulator doesn't have an arc tangent function. to get the same effect you do inverse tangent. .ie 1 / tan(x). to be honest, i dont remember why i have the "90 -" part of the formula there. This was done some years ago. Basically what i did was worked it out using the windows calculator.. then whipped up a quick C++ program to spit out the numbers, then dropped it into an XML file to print it.

in windows calculator you'd do this for fast mk.14 vs 9 kt ship:
46 / 9
hit the = button
hit the Tan button
hit the 1/X

again i cant remember what the "90 - " was for.

anyway, i need to update that table one of these days. First off the table assumes Mk.14 torpedos (31kt slow, 46kt fast). and secondly i need to extend it off to the right for Impact AOB's other than 90, as i dont really try to set up for perfect 90AOB shots anymore now that i've grown found of the american TDC and find myself actually using it. .ie i dont line up perfectly at 90AOB and wait like a duck.. i'm always on the move manuevering now. though every now and then i find myself in a situation where i fall back on the table for hip shots. gives me a rough idea of how much i need to lead for a given target speed.

[gutted]

... is directly responsible for the Dick O'Kane technique and indirectly responsible for all the other constant bearing techniques and wrinkles I have developed.

you can call it whatever you want.. but im still calling it fast 90.

*runs away screaming*

[gutted]

Originally Posted by I'm goin' down

that explanation was too confusing for me to follow. Rockin Robbins provided a simple explanation. see posts 41 & 42..

maybe a picture will tell it better.


my way:
draw two lines, and measure one angle. set your scope that many degrees from 0.

robbin's way:
Draw a line, measure the AOB & Range for that line.. and play with the Dials to match it.

either way works. i just dont like playing with the dials for this type of shot. :P

edit:
now that i think about it.. i guess i should have put arrows on the lines. the target in these examples are move left to right.. and ownship is moving bottom to top.

[Rip]

Originally Posted by Rockin Robbins

I dunno. I think he took the shots as the situation dictated and wrested the odds as best he could. It's not like you look at an unfavorable position and say, "Nope. I don't like that angle."

Statistical analysis shows that a torpedo track angle of roughly 110º (varies with speed) is the most tolerant with regard to errors in calculating target speed. Reverse analysis of their mumbo-jumbo showed that firing at AoB 90 or slightly afterward was best for that.

As far as maneuvering out of the way of the torpedo, a torpedo track angle of 90º would be the best because the target has to turn just as far in both directions to avoid.

Let's reason this out. You're firing a John P Cromwell attack from 45º ahead. That ends up giving you an AoB of about 35º starboard or port depending on which direction he's coming from. The sharpest he has to turn to get his bow toward the torpedo and then be able to turn left or right to avoid is.....45º, right?

OK, let's take the O'Kane situation. The torpedo approaches from 30º or more aft of the target beam (torpedo track angle of 120º or slightly more). We'll assume the target is moving left to right. Since the torpedo is approaching from aft, the speed of the target makes the approach speed of the torpedo slower, giving the target more time to react. Then the target needs only to turn 60º to port, hit the throttle and maneuver left or right to let the torpedo, now on a parallel course, pass starboard or port.

I don't understand O'Kane's reasoning there. I'd rather be firing from ahead of the target if I can't pick the 90º attack, so that I have lots of wiggle room in my calculations and can absorb maximum error. Failing that I want the target to have minimum time to react if he sees the torpedo.

Well I went back and found the spot. Page 202 reads:

At 0455 it was light enough to see through the scope, and finally two blasts took us down, pausing while a final radar range and periscope bearing fixed her position. Both Chan and Richie agreed on an enemy speed of 9 knots instead of ten. Captain Morton had readied two tubes forward and aft, and now ordered the forward doors opened; it would be a bow shot. Her port angle was opening as it should. I heard Richie advise, "750 yards from the track, as I called 90 port.

The captain waited for an approximate 120track, the aspect that would allow maximum enemy maneuvers and still insure that our torpedoes would hit, and then said, "Any time, Dick. Fire just one torpedo."

I remembered it because it was opposite of what I would have thought as well. I am a submariner but we would just steer them with the wire or chnge acoustic modes.

[Frederf]

Originally Posted by gutted

though techincally, it was less than 90AOB

I figured that's what it was, a 90° torpedo track angle shot which means 10-20° visual lead.

As for arctan, invtan.. im no mathemetician, but aren't they are the same thing.

Yeah, same thing.

[I'm goin' down]

If you are firing at zero bearing, all you have to do is make sure that your lead angle is at least large enough that is equals or exceed the distance (i.e. yards/meters) the target can travel over a 3 minute interval? For example, if the target is travel 10 kts, covering 1,000 yds. over 3 minutes, and you want to have impact at a zero degree bearing, the firing point is as follows:

For a target approaching from your port side, the firing point is that point

1. on the target's course where the angle, created by running down the course line 1,000 yds. from the point where the imaginary line extending from the zero bearing crosses the target courses,
2. intersects with the firing point?

[gutted]

Originally Posted by I'm goin' down

If you are firing at zero bearing, all you have to do is make sure that your lead angle is at least large enough that is equals or exceed the distance (i.e. yards/meters) the target can travel over a 3 minute interval? For example, if the target is travel 10 kts, covering 1,000 yds. over 3 minutes, and you want to have impact at a zero degree bearing, the firing point is as follows:

For a target approaching from your port side, the firing point is that point

1. on the target's course where the angle, created by running down the course line 1,000 yds. from the point where the imaginary line extending from the zero bearing crosses the target courses,
2. intersects with the firing point?

im not following you.

it's the angle created by the ratio of your torpedo's speed to the ships speed as in the picture i posted earlier. note: the start of the 46 line does not originate from the center of your ship... your ship could be anywhere on the line. you will most likely be closer than 4600m (If using 100m scale)


another way would be be to measure the distance to the impact point from your nose. figuring out how long it would take your torpedo to reach it. Then figuring out how far the enemy will travel in that time period And measure the angle from impact point, your ship, and imginary target ship.

that way takes too much effort.

[Rockin Robbins]

Frederf: you're really onto something there with your assumptions, and there is something that the game would differ markedly from real life. An example I am familiar with is that Japanese destroyer captains were trained that Americans were right handed and that underwater evasion maneuvers were always to the right. (source: Japanese Destroyer Captain, Capt Tameichi Hara). Eugene Fluckey knew this and routinely turned left.

Concentrating on maneuvering conventions alone (for no particular reason, just picking one of the four), suppose the merchants were trained to turn to port to avoid. We'll talk about targets traveling from left to right here.

That being the case, if you shot before AoB 90, from ahead of the target, the target would see the approaching torpedo, turn left and diminish his cross-sectional area from the torpedo's point of view. This would greatly diminish the chance of a hit, and my experience with John P Cromwell shows that if they turn into the path you get almost no hits.

Gutted has talked about what us astronomers call "proper motion," that is the component of apparent motion from left to right (or right to left) from the point of view of the observer, who has no idea of the angle between the target's path and your path. Well, if you do the math on a 45º shot, our proper motion is 70% of the actual speed of the target. However if he succeeds into turning into the direction of the torpedo (straight at us!) his proper motion is exactly zero! He's stopped. The torpedo passes harmlessly to his right because it is programmed for the apparent speed, the proper motion, of his original course.

Now lets take the situation where you shoot after AoB 90 and the torpedo is approaching from astern of the beam. Here, if the target turns left, he turns broadside to the torpedo, presenting a much larger target to hit, thank you very much, he has suddenly made his situation much worse and BOOM!

If such an assumption were built into the game, and I haven't seen any evidence that it is, it would also be very important to set up assymetrical spreads to compensate for expected reactions. For instance, if firing from ahead and expecting him to turn into the direction from which the torpedoes are being fired, it would be important to fire a trailing shot that would miss a target which stays on course but would tag the target which turns in the anticipated direction.

Real skippers did that a lot, which explains a lot of their misses. Those weren't misses due to poor shooting, those were cover shots, ensuring a hit in those "what if" situations. Wasting topedoes to save your life ain't a bad proposition!

I could cover the other possible assumptions, but I think the general idea is here. Too bad I don't see any evidence of that behavior in the game. It was vital information in real life.

[Pacific_Ace]

RR sez:
"Now lets take the situation where you shoot after AoB 90 and the torpedo is approaching from astern of the beam. Here, if the target turns left, he turns broadside to the torpedo, presenting a much larger target to hit, thank you very much, he has suddenly made his situation much worse and BOOM!"

I sez: I'm thinking this through in my head and coming up with 'thats only valid if he's turning into the direction the shot came from'. If he turns away, he is showing you his stern and reducing cross-section.

[Rockin Robbins]

Originally Posted by Pacific_Ace

RR sez:
"Now lets take the situation where you shoot after AoB 90 and the torpedo is approaching from astern of the beam. Here, if the target turns left, he turns broadside to the torpedo, presenting a much larger target to hit, thank you very much, he has suddenly made his situation much worse and BOOM!"

I sez: I'm thinking this through in my head and coming up with 'thats only valid if he's turning into the direction the shot came from'. If he turns away, he is showing you his stern and reducing cross-section.

That's true, but in this situation he would have to turn right to do that. I've already positied a rule that Japanese merchie captains turn left when they see a torpedo.

It seems to me that if there were a merchie rule, I'd make it that if the torpdeo approaches from aft of the beam you turn away, if from forward of the beam, you turn toward. However, I was working from the theoretical rule that frederf put into his post, just to illustrate that just like in real life we could anticpate habits of the enemy and turn them into sinkings.

Unfortunately, I have seen very few habits other than the dragster behavior when torpedoes are sighted.