Sub Skipper's Bag of Tricks

[Distortion]

Yeeeaaah, on my 1st patrol, using the vector analysing, I`v got myself a nice Kongo class ship, and sink it with 3 torpedo`s. It was a convoy of about 2 Kongo`s in the middle, defend by some destroyers, and cruisers. My first plan was to use slow and fast torpedo`s, and put both kongo`s out of action. That didnt worked well. For the first kongo I used slow torpedos, with a speed of 31 knots. For the second I used fast torpedos with a speed of 46 knots. The speeds of the targets was 14.5 knots. I draw 2 line for the torpedo speed, one 3100 yards, the other 4600 yards, and calculated the lead angles. Strange thing it the slower ones didnt hit the target, the fast ones did. What gives? Do I need another tactic with this one?

thanks guys

Robert

[Rockin Robbins]

Error tolerance, man! When you're out there bobbing around in the big green ocean, there are errors in every measurement you make, especially in target speed. Warships love to speed up and slow down, zig back and forth and generally screw up our magnificent vector triangles. And they are moving fast. A small error can make us miss, not just hit an unplanned part of our target.

So everything we do in putting together an attack plan should have one goal in mind: mitigating the effects of inevitable error. The absolute BEST factor in that is torpedo speed. The faster the torpedo speed, the more error tolerant your solution.

Three rules for maximum error tolerance:

GET CLOSE a shot from 700 yards gives the enemy almost no time to avoid and is twice as error tolerant as a shot from 1400 yards.

WATCH YOUR TORPEDO TRACK ANGLE that's the angle at which the torpedo strikes the target. The closer to 90º the torpedo is, the more error tolerant your solution. As mentioned above in another post, there are reasons to toss this one out the window with warships.

USE THE SMALLEST POSSIBLE GYRO ANGLE preferrably zero, with the vector analysis attack. This eliminates range from the solution and is possibly the most important factor in mitigating error if you have no radar.

USE FAST TORPEDOES discussed above. The faster you can get the boom to the target the less time there is for something to go wrong. And the difference in impact point along the target length for a given error is larger or smaller in proportion to the torpedo speed, with the faster torpedo having the least variable impact point.

One, two three.........more than three. See? There is error in my targeting solution. And a final thought: you're going to have some misses. I have lots of them. If all you shoot is the sure things, your score isn't going to be very good. Take your misses with a smile and learn from them. No guts, no glory.

[Distortion]

I`l guess you are right, I trust to much on my calculations, and the fact that the enemy screw things up. Thanks for your tips, really appreciate it.

[Frederf]

Originally Posted by Rockin Robbins

WATCH YOUR TORPEDO TRACK ANGLE that's the angle at which the torpedo strikes the target. The closer to 90º the torpedo is, the more error tolerant your solution.

How do you explain this diagram?

[Don_D_Dwain]

Hello Guys,
I did not see this in the thread, but I just skimmed over it , so if it is there, please disregard this comment. As you probably already know, the Germans developed the first homing torpedo. One of them, the G7es (Falke), was used but reports that it was too slow to be useful (20 kts), and the target vessel needed to be going at least 12 kts (I think), for it to home in on. When I go out for a patrol, I have one of these fish in my rear tube (lol, ok no pun intended), just sounds funny. If you should happen to come across a Pesky escort that will not leave alone, or if you absolutely have to get rid of him, then try this. WARNING: it is a VERY RISKY tactic. At a distance that you determine is safe enough for his GUNS not to hit very accurately, at you stern, you SURFACE, to let him see you. Make sure your stern tube with the FALKE is open. When he gives chase, SUBMERGE to Periscope Depth, and turn till he is about 180 Bearing. Remember, this is RISKY. Take a set of Range, Bearing and Speed, all does not need to be very accurate, as long as he is close to 180 from you. Now, the same as when a cop is running radar, he will see you, and the chase is ON. Let him come a bit closer, launch your FALKE, and shut your engines off and DIVE. The rest is HIS LUCKY DAY. Thanks.

[Rockin Robbins]

Originally Posted by Frederf

How do you explain this diagram?

OK, I've gotta hit the books. I want to be right and easily understood on a graph that's darned difficult to read! Stand by......

Beginning to understand...... Processing.....

[magic452]

@ Distortion Good work on the vector shots, to get two different ships at once takes a little practice.

You can shoot both a 31 Kn and 46 Kn vector solutions at the same time.

What I do is approach the target course line at about 60° AoB.

For a convoy pick a target in the first column for the 31 Kn shot and a target in the second column for the 46 Kn. shot. With a 60° AoB the two ships will almost overlap at the time you shoot. The slow speed will hit first so you must adjust your targeting towards the stern of the second to allow for it slowing down. Did this just yesterday for a total of 18,000 tons, two very large freighters. You want to shoot from about 1,700 yards so the high speed torps have a chance to catch up with the slow ones.
With a little experimenting with the range you should be able to get almost simultaneous hits on both ships.

What Rockin Robbins says is very true, You must get very good speed and course data and be able to adjust for conditions and errors.
With a 60° approach you must get everything right, there is little room for error. When trying to shoot both high and low speed the range is critical so you get near simultaneous hits and it takes somewhat longer ranges to do this.

As with any firing solution, conditions play a big part, very good visibility may allow the target to see the torpedo wakes and start to slow and turn.
If possible I will tail the convoy and try to set up a night attack.

Haven't tried this against warships yet, they are a different can of worms.
They see the torpedos sooner and react faster than merchants.

I may have a shot at it tomorrow. Setting up on 5 ships running line astern. Don't know what they are yet but looks like warships. I have an early save so I can try different set ups. This will be a night attack so I think I can pull it off.

Good luck and good hunting. Stick with the vector shots I think you will like them.

Magic

[Distortion]

@ Magic

Thanks for your reply. But if you know the distance between the two vessels, and if they running the same speed, I thought it is possible to just arrange the heading of the periscope, hit the send button again, and fire the other two fast torpedos? Problem is, how do I plot that on the map?

[Rockin Robbins]

OK, here's the deal on Frederf's chart above. If you think about it, your lead angle changes, depending on the angle on the bow of the target. To take an extreme example, when the AoB is zero he's headed straight toward you. There is no lead angle at all! You just set speed to zero or AoB to zero and if your bow is pointed at the target, out comes a zero gyro angle shot.

However, when you are at AoB 90, the target has the highest apparent motion from left to right or right to left and you must make a maximum lead angle ahead of the target bearing to achieve the boom.

So you can see that as the target approaches, the lead angle is constantly changing. However, the graph doesn't graph target bearing. It graphs torpedo track angle. You may swear now. Oh, they're not tracking real torpedo track angle, but pseudo torpedo track angle! @#$@#$%@#$ I'm going to have to pull out a chart here.....



Now your sub is on the right end of the sub's course line. Yeah, I know that's not obvious. Why didn't they just SAY SO???. Point P is the periscope. The middle line between M and P is the bow of the submarine. Point M is the end of the torpedo's straight run, where it turns to its set gyro angle along the curved course to the torpedo track toward the target. Kapeesh?

Actually that's not going to matter much, because in the special case these graphs show, the deflection angle is exactly equal to the periscope lead angle. They don't explain that in the Submarine Torpedo Fire Control Manual, they just claim that "From a study of the curves it is evident that..." NO, IT"S NOT EVIDENT!!! THAT"S WHY WE"RE LEFT WITH THESE FREAKIN' QUESTIONS!!! Thank you, I feel much better now.

To further muddy the waters, the manual doesn't say what the optimum periscope bearing to fire is, it relates everything to the resulting angle the torpedo takes when striking the target, measured from zero at the bow to 180 at the stern. So to make any sense out of what they say you have to reverse engineer all the gobbledygook.

I've done that. You're going to laugh. All the charts can be used to start campfires or something. Let's take the chart you used above.



Let's take the bottom curve, for 8 knots. The deflection angle is the exact same as our lead angle because they're all zero gyro shots. It says if the track angle is zero (you are shooting directly at the bow), the deflection (lead) angle is zero, you don't have to lead the target at all.

But as the angle on the bow, which is a bit less than the deflection angle, increases and the target bears more and more boadside the lead angle increases until you get to the optimum track angle, where the curve levels off and starts to fall again.

In the shaded area, between a 90º track angle and the next radial line over, where the lead angle is again the same as a 90º track angle, the lead angle changes least for each degree of target bearing. So shooting a torpedo track angle in that range will give you the most error tolerance possible. Gee, I think I've talked about building error tolerance into our attack plans before!

Well, all thse graphs are very fine and great for impressing girlfriends over dinner if you've run out of things to talk about, but what in sam hill do they mean? You're gonna die...

Shoot from a course at right angles to the target track, ala Dick O'Kane and fire when the target bears 0º. The torpedo will automatically (if your TDC is set for AoB 90º and correct target speed) take the optimum track angle toward the target. If you care about the resulting 10º to 20º gyro angle (you shouldn't worry about gyro angles of less than 30º) you can alter your course to about 110º from the target track instead of 90º. This will reduce your gyro angles in all reasonable circumstances to less than 5º. I'm not going to worry about it myself.

Now you can go make paper airplanes from those pretty graphs and use them to entertain children. Yup, there's the right way, the wrong way and the military way. Welcome to the military way to make the simple into brain surgery...

[Frederf]

You know I've been looking at the graph I posted and even half-arse using it in SH4 for a while now but I've always put off applying some greygoo power to it until you splattered against it first.

When I saw deflection angle on the plate I remembered it was back in that previous diagram in the same document about the angle between the periscope and pseudo-winkler-bajoob or something and never bothered to look it up. It turns out the deflection angle is more or less what we've been used to thinking of as the "shoot lead angle" or the angle between the direction to the target visually at the moment of firing and the direction of torpedo travel.

Oddly enough I've been using the concept of "optimal track angle" for ages in Silent Hunter but in a totally different context. I never thought of it as the most error-tolerant or the least rate of change of deflection angle but simply the best chance to hit another ship in a convoy row if I missed the first target.

If you try to hit a convoy target squarely and miss astern there's no chance to hit his neighbor traveling abreast of him. So instead of perfectly abreast of a convoy row I'll skew the shot (or spread) several degrees beyond 90° impact then a miss of the first can hit the second or even third. The improvement in hit percentages is very noticeable! For example if the convoy is going 10 kts I would shoot at a torpedo track angle of ( ArcTan (10/46 ) = 12.3°) 90 + 12.3 = 112.3°.

I had the suspicion but never a firm understanding that when firing in this way not only was I increasing my chances of hitting a 2nd or 3rd target I was actually increasing my chances of hitting the 1st or single target.

Let's check this method vs. the plate and see if they agree.

D'OH WRONG: TORPEDO TRAVELS ALONG THE HYPOTENUSE

ArcTan(8/46)+90° = 99.9°
ArcTan(12/46)+90° = 104.6°
ArcTan(16/46)+90° = 109.2°
ArcTan(20/46)+90° = 113.5°
ArcTan(24/46)+90° = 117.6°

What's with me and Tangent vs Sine lately?

BETTER

ArcSin(8/46)+90° = 100.0°
ArcSin(12/46)+90° = 105.1°
ArcSin(16/46)+90° = 110.4°
ArcSin(20/46)+90° = 115.8°
ArcSin(24/46)+90° = 121.4°

Plate
8kts: 102
12kts: 108
16kts: 111
20kts: 118
24kts: 122

Hmm I was hoping those would come out closer. It's probably just a coincidence that these values are close.

I think of it this way: If you know the enemy's course very, very exactly and know the enemy's speed very, very poorly my best shot is against the target's bow or stern to rule out errors in speed. However if you know the speed very well and the course not so well it's better to shoot into his sides as his ( angular speed ) x ( target angular width) is not so strongly tied to his AoB the closer you get to 90°/270° AoB. Somewhere between these two extremes must be a balance for an equal uncertainty both with speed and course.


This of course all goes out the window because with these darn faulty impact pistols I am habitually shooting from 50-60° torpedo track angle or 120-130° to avoid the square-shot pistol jam dud-amabobber!

[magic452]

@ distortion

To shoot a true vector analysis solution you will have a 0° gyro angle, speed = 0 and AoB = 0 and bearing = 0. The only time you hit the send button is to set these values. A 0 gyro angle will send the torpedo right down your course line. If you move the scope to any bearing other than 0° and hit the send button you will change the gyro angle and therefore the torpedo track.

Once you have your shooting bearings just point the scope to that bearing but don't hit the send button. Fire when the part of the target you want to hit is in the cross hairs. Wait till the second target gets to it's shooting bearing and do the same. The two targets must be very close to each other for this to work, that is why I shot at ships in two different columns at a 60° approach.

I tried to get a single column type of shot off today but no way it would work, too much distance between the targets. By the time I was able to shoot the second ship it had already reacted to the first being hit and changed course and speed.

What I had was a large troop transport (9494 tons) followed by about 200 yards by a DD (2700 tons) and that followed by a very large transport (18765 tons) by some 1,400 yards.

I shot the first ship with a 31 knot vector shot and then just adjusted a few degrees and shot the DD, both sank. For the other transport I just used a position keeper shot as he was slowing and turning, got him also.

Not a bad days work, almost 31,000 tons with only 6 torpedos and not a single DC dropped any were near me, shot from 2800 yards.

As far as sending a different gyro angle to shoot a second ship I don't know how you could plot that out. But it may be worth a look and see if it
can be done. Darn it now you got me thinking and it hurts.

You might be able to do something like that with the O"Kane method but I don't use that so I don't know.

Magic

[TwinStackPete379]

I just did my first O'Kane fast 90 after reading RR's tutorial. out the stern tubes at 2600 yds. that was way cool! both fish hit EXACTLY where i aimed for. that was FUN, I wanna do it again!

[Rockin Robbins]

And there are lots of other factors to be concerned with than just how tolerant of target course errors our solution is. For instance against warships, I believe you want the John P Comwell shot from ahead of the target, because every second you wait to shoot is a second during which they might detect you. When they do, all that beautiful data you've collected is in the garbage and you don't care HOW accurate it was...

Also there's the error mitigating fact that the faster the torpedo's approach speed to the target, the smaller the error radius of the impact point. Using the roughly 110º torpedo track angle, the torpedo is approaching the target from 20º aft of the beam. So from your 46 knot torpedo speed you must subtract some of the speed of the target to get the torpedo approach speed.

Similar to the way speed is added to torpedo speed by the target's approach in the John P Cromwell technique, the approach speed of the torpedo must be reduced by the speed the target is receeding from you at point of impact. Well that is calculated by the cosine of the 110º torpedo track angle, .34 in round figures. So the 31 knot approach speed of the torpedo must be reduced by 34% of a 20 knot target's speed! That leaves the already anemic electric with an approach speed reduced by 6.8 knots! And with a target approached at only 24.2 knots, there is all kinds of time to ruin all your beautiful numbers.

The graph shows a very incomplete view of all the decisions you must make during an attack. I question their usefulness as a practical matter.

[Distortion]

Yesterday I`v been working the hole day with the numbers. the first target is not a problem, can hit it at 1k-2k-3k yards, slow or fast torpedos with the vector analysis attack. I tought it can`t be that hard to hit the second target, witch course and speed it the same than the first one. But it is very complicated, without turning your own sub. Afcourse, when I turn the periscope away from the 0 dergree point and send the new calculation, its not an vector analysis attack anymore, but who cares. If I know course and speed, it can be that hard? How much degree need I for the second target, what is the lead angle, etc.

I have some calculations, and I think I was very close yesterday. Tonight I will try another round, with new ideas (yes, when in bed new ideas came up) based on those calculations, and see what happens.

I do have a problem with the 3000 yards bearing plotter i use, its not for 1680 X 1050, so its off by 1 degree. And this can be a problem at high distances. Anyone here can help me with that? I`v asked this question also here http://www.subsim.com/radioroom/showthread.php?t=132000.

We will continue..., thanks for all the input guys

Robert

[Hitman]

Fantastic explanation RR

On this piece I wanted to add a small comment:

you can alter your course to about 110º from the target track instead of 90º. This will reduce your gyro angles in all reasonable circumstances to less than 5º. I'm not going to worry about it myself.

The manual for the Attack Course finder uses an example to illustrate how it works and do you know what track angle is chosen? Bingo .... 110º

I quote the manual:

5. EXAMPLE: Heading by compass 230 degrees. Enemy relative bearing by periscope 315 degrees. Angle on the enemy's port bow 25 degrees. Estimated range 5000 yards. Desired track angle 110°.

Good proof of how right you got it