"Snap Shot" -- to answer your question Johnfb

[Alfred Keitzer]

Arg!!! I had written a rather lengthy reply to you question and when I went to post, Hitman had just closed your topic. So now you get the short answer.:yeah:

First off, with TDC ON, misha1967 provided some very good input. He is right, AOB and Target Speed are the two most important ingrediants for the solution. Range not so much, but I must forgo that discussion for now. Here's the quick and dirty for a 90-AOB "snap shot" with TDC speed set to zero. Good to about 30-35 degrees off the nose or tail (stern torpedoes) -- beyond that, torpedo straight run comes in play (more lead required). Also note this is for approximately 90-AOB. Anything else, the sine of the AOB comes into play.

The 90-AOB "snap shot" with TDC ZERO SPEED SET --

1. Go to Attack Map and turn TDC OFF
The little button marked "1" and "0"; "0" is TDC OFF
2. Set Target Speed to Zero on TDC
Very important -- now torpedo run is determined by periscope look angle after you ...
3. Turn TDC back ON.
Very important -- TDC must be ON to feed periscope look angle to the torpedo
4. Estimate Target Speed
Slow Convoy -- 6 kts
Medium Speed Convoy -- 9 kts
Fast Convoy -- 13 kts
-- or -- better yet, best to get a good target speed from observation and know ahead of time.
5. Select torpedo and torpedo speed

6. Calculate Lead
SLOW speed torpedo lead = 2 x Estimated Target Speed
MEDIUM speed torpedo lead = 1.5 x Estimated Target Speed
FAST speed torpedo lead = 1.3 x Estimated Target Speed
7. Open torpedo door to eliminate launch lag

8. Lead the center of the target by the lead angle computed in step (6.) above with your periscope

9. Fire

For each subsequent torpedo, open torpedo door first, lead target with periscope, and fire.

Don't forget to turn TDC back ON after you set the Target Speed to zero.


Sorry, I would explain how I got all this but I gotta run for now.

[Johnfb]

Thank you for taking the time to post
:yeah:

[Alfred Keitzer]

OK, I'm back. Now I'll give you the long answer if you're interested as to where I got these numbers.

First, keep in mind that the Type I torpedo has three speeds: SLOW (30 kts), MEDIUM (40 kts), and FAST (44 kts). Most other torpedoes run only at the SLOW speed of 30 kts. I always carry a decent number of Type I torpedoes because I like the fast speed (smaller lead) of these torpedoes.

Second, I should note that I only use the "snap shot" in close -- 600 to 1000 meters. If the target is at range, I figure I always have time to do a decent TDC solution.

So here's an example and you'll want a Type I torpedo selected to do this. No target is required for the demo.

Make sure your periscope is pointing straight ahead -- 0 degrees relative. Next, go to the Attack Map (F6) and turn TDC OFF; set Target Range to 2000 meters and Target Speed to 0. Now the torpedo run line on the Attack Map should be straight out the bow of your boat if your periscope is pointing straight ahead.

Set the Type I torpedo speed to (S)LOW.

Now set the Target AOB angle to 90 degrees (right or left makes no difference) and set the Target Speed to 6 kts. Note that the torpedo run line is now 13 degrees left or right of your nose (depending on whether you set left or right AOB). This is your lead angle.

Now run the range up and down. Note that the lead angle does NOT change. As stated by misha1967, this just illustrates that Target AOB and Target Speed are the two most critial elements in your lead solution -- Target Range is not.

Put the Target Range back to 2000 meters and change the Type I torpedo speed to (M)EDIUM. Now notice that the torpedo run line (lead angle) is about 9 degrees. Change the torpedo speed to (F)AST and note that the run line (lead angle) is about 8 degrees.

So what have we learned ...

For a 90-AOB shot against a target going 6 kts the lead angle is:

13 degrees for SLOW torpedoes (approximately 2 x Target Speed)
9 degrees for MEDIUM torpedoes (approximately 1.5 x Target Speed)
8 degrees for FAST torpedoes (approximately 1.3 x Target Speed)

... and Target Range has negligible effect on the solution unless target bearing off the bow (stern) is more than 30-35 degrees relative -- remember, the torpedo straight run issue.

You can repeat this for different Target Speeds ...

For Target Speed = 9 kts, the lead angles are 18/13/12 degrees for Slow/Medium/Fast torpedoes respectively; and for a Target Speed = 13 kts, the lead angles are 26/19/18 degrees for Slow/Medium/Fast torpedoes.

... and you'll find the relationships hold pretty true for a 90-AOB "snap shot":
SLOW torpedo lead angle = approximately 2 x Target Speed
MEDIUM torpedo lead angle = approximately 1.5 x Target Speed
FAST torpedo lead angle = approximately 1.3 x Target Speed
Now, if you really hot, you will remember that ...
For AOB = 60/120; sin(60) = .866 (I use .9)
For AOB = 45/135; sin(45) = .707 (I use .7)
For AOB = 30/150; sin(30) = .5
... and apply this multiplier to your solution if you don't have close to a 90-degree AOB solution. Just remember, because of the torpedo grazing angle, if you're going to shoot much off the 90-degree target crossing angle, you will want to go under the hull with the influence fuze. In general practice though, applying AOB adjustments requires too much brain power for me :o -- which is why I usually reserve the "snap shot" for close in, close to 90-AOB situations ... but it does come in handy for a zigzagging target, in which case, I usually stay close to the target; pick a solution; and wait for the target to give me the AOB I'm looking for.

Just don't forget that Angle-Off-Bow is your relationship to the target -- your position off the TARGET's bow.

Good luck!

[Bubblehead729]

That's a really interesting tactic. I'm gonna have to take that one for a test drive...I can really see that coming in handy sometimes. It never hurts to have another card up your sleeve. Thanks for the write-up! :rock:

[Alfred Keitzer]

Yikes, I need to get back out to sea -- I've corrected my first post, but originally left out a most important step (3.) ... you turn the TDC off momentarily to set the target speed to zero. You do this so TDC will have no impact on the computation of lead angle.

But after setting target speed to zero, you MUST turn the TDC back ON so the TDC will follow your periscope look angle -- it will not when the TDC is off -- and you want to use the periscope look angel to lead the target and adjust for the lead angle required.

[Bubblehead729]

But after setting target speed to zero, you MUST turn the TDC back ON so the TDC will follow your periscope look angle -- it will not when the TDC is off -- and you are now using the periscope look angel to lead the target and adjust for the lead angle required.

So after chewing on this for a bit, I want to make sure I'm understanding you correctly...I should leave the periscope trained to 0 degrees relative, and shoot as the target passes the correct relative bearing for torpedo and target speeds. (for example 9 degrees for a medium speed torpedo at a 6 knot target passing right to left). Because if you turn the scope to a different bearing with the TDC engaged, you are altering the gyro angle, and changing your solution.
Have I got that right? Or am I missing it? (the point and the target :D)

[Alfred Keitzer]

Not quite -- you can do it that way, but not required. You don't have to leave the periscope at 0 -- that was just for the demo so you could see the lead (off the nose) computed for different target speeds; and to show you how range has little to no effect on lead angle provided you are shooting within 30-35 degrees of your bow (or stern).

Momentarily turning the TDC off, you have control over the TDC settings. Setting the target speed to zero causes the TDC to compute zero lead angle -- because it thinks the target is not moving. With target speed at zero and turning the TDC back on, the path of your torpedo is now determined purely by where you point the periscope.

So for your example -- target going 6 kts passing right to left using medium-speed torpedo ...

MEDIUM torpedo lead angle = approximately 1.5 x Target Speed = 1.5 x 6 kts = 9 degrees of lead angle.

You've set the TDC OFF; set speed to zero; TDC back ON. Looking through your periscope, you see center target bearing 020 relative. Lead the target with your periscope by 9 degrees -- point your periscope at bearing 011 degrees relative -- and shoot.

Don't forget to open the bow cap (torpedo door) before you shoot. For a target at close range, it can move several degrees in the time it takes to get the bow cap open.

-------------------

To answer your second question -- yes, you are altering the gyro angle with your periscope, which is exactly what you want to do -- you want to alter the gyro angle to lead the target by some number of degrees that you've computed in your head. The only difference between a true TDC solution and the "snap shot" is you are computing the lead based on torpedo speed, your best estimate of target speed, and a rule-of-thumb calculation and using the periscope to apply that lead against the target.

[Bubblehead729]

Ahh ok that clears it up. Thanks for the explanation; looking forward to trying this method out.
:rock:

[von Kinderei]

Very well explained ... :up:

[misha1967]

Thanks, Alfred, for adding that.

Because the "lead" method gives you the additional opportunity to fire off your shots right now as opposed to wait for the target to move into your crosshairs, and that's damn good info for those situation where you have everything else on the money but don't have the time to sit around and wait. :yeah:

[Alfred Keitzer]

It all sounds easy in theory, but in the heat of battle, it's easy to forget steps. That's why I try to setup well in advance for the attack. The first thing I do is work to establish a good estimate of target speed. I then look at my torpedo inventory and decide what torpedo speed I am going to use. To keep it simple, I try to use one torpedo speed so I only have to remember one lead computation. I then preset my torpedo speed and depth for all torpedoes. With good Target Speed, Torpedo Speed, and depth set, and having computed my "snap shot" lead ahead of time, I'm now ready for the attack.

Once I determine I am going to "snap shoot", I turn TDC OFF; set Target Speed to zero; and TDC back ON.

I then have a four-step plan for "snap shots". I use this plan religiously because Step #2 (open bow cap) was always the easiest to forget and it will just ruin your day. I use the keyboard so I don't have to keep clicking the mouse between periscope and everything else -- I use the mouse exclusively for periscope work when doing "snap shots".

1. Select ready torpedo {keyboard "Y"}
2. Open bow cap {keyboard "Q"}
3. Find target and note bearing
4. Apply computed lead angle with periscope and shoot {keyboard "Ctrl Enter"}

REPEAT Steps 1. through 4. for each target.

Now as I remember, launching a torpedo in the stock version of SH3 is just the "Enter" key, but I use GWX 3.0 where the command is "Ctrl Enter". Sorry, I don't remember what the command is using NYGM.