Sunk my FIRST Destroyer!!!!!

[ddiplock]

Yeah yeah, i know what you fellow Kaleuns are going to be saying "you sunk a destroyer, so what? Its hardly the HMS Nelson now is it??" :)

Well you'd be right, its not the mighty battleship Nelson, or any form of large British warship. But its a warship nontheless, and one that shall never plague the U-boats again!!!! :D Heading South-West down into the Hebridies, a favourite route I take on every patrol I spotted a lone V&W class destroyer heading my way. I dove on down to periscope depth and rigged for silent running. She was heading straight for me, but she hadn't seen my boat and had NO idea I was waiting for her :) It was almost like a scene from Das Boot!!!

I've always been weary of doing speed calculations on warships, for although they always seem to be moving slowly, on the nav map it shows a different story. I did the usual 3 minute 15 second calculation, she'd travelled 1km in that time, so I calculated her speed on the nomograph to be at about 6 knots, which I popped into the TDC. At the last minute I realised my boat was still facing the wrong way, and I hadn't turned to fire at the destroyer abeam. I quickly went to full rudder and slowly began to creep into my firing position.

Realising however that the destroyer wasn't going to wait for me, I decided to take the shot. I opened tube 1, did a quick calculation on range, bearing, AOB and speed and input it all into the TDC and then fired. Given the fact my boat was still turning when i was gathering my data I really had no idea if the torpedo was going to hit or not.

The torpedo struck home!!! Underneath the destroyer forword of the ships props. The explosion ripped into the weak underside and somehow the aft mast of the destroyer was blown clean off the hull!!!! I couldn't help but smile as she quickly sank on her journey to the depths. It was only a destroyer yes, but god did it make me smile being my first one sunk :)


NOTE: There was a time in a previous career I did come across my first Battleship. Things couldn't be better and I got to within 800 meters of her, unfortunatley the seas were heavy, a wave broached over my conning tower revealing it and all hell within the task force erupted. I was forced to dive the ensuing DC attack, and never saw another battleship again :( Even now task forces when I try to intercept them, even though they're heading for me always seem to "dissapear" and never show themselves. :( A pity

[Puster Bill]

I did the usual 3 minute 15 second calculation, she'd travelled 1km in that time, so I calculated her speed on the nomograph to be at about 6 knots, which I popped into the TDC.

:hmm:

The idea behind the 3:15 rule is that it allows you to equate hundreds of meters travelled during that time to speed in knots. If the destroyer travelled 1km in 3:15, that would be 1000 meters/100 = 10 knots.

Congrats on getting the destroyer, though. They are tough to hit because they are fast and shallow. The only times I've been consistently successful is when I let them get within 500 yards, then fire magnetics at them.

Still, conventional wisdom is to leave them alone unless you absolutely have to sink one. The nice thing is that you get to choose.

By the way, get a whiz wheel. They make AOB and speed calculations a breeze:
http://www.subsim.com/radioroom/showthread.php?t=114351

My preference is for the physical version, but there are Flash and in-game versions available.

[ddiplock]

I did the usual 3 minute 15 second calculation, she'd travelled 1km in that time, so I calculated her speed on the nomograph to be at about 6 knots, which I popped into the TDC.

:hmm:

The idea behind the 3:15 rule is that it allows you to equate hundreds of meters travelled during that time to speed in knots. If the destroyer travelled 1km in 3:15, that would be 1000 meters/100 = 10 knots.

Congrats on getting the destroyer, though. They are tough to hit because they are fast and shallow. The only times I've been consistently successful is when I let them get within 500 yards, then fire magnetics at them.

Still, conventional wisdom is to leave them alone unless you absolutely have to sink one. The nice thing is that you get to choose.

By the way, get a whiz wheel. They make AOB and speed calculations a breeze:
http://www.subsim.com/radioroom/showthread.php?t=114351

My preference is for the physical version, but there are Flash and in-game versions available.

Well, I used the ruler to measure the distance between the points and it measured the distance as 1. Now can that be interpreted as 1000 meters or 1km?? I'm wondering how close my speed calculation was, i can't have been THAT wrong if the torpedo hit :) But having said that they were not that far away, so being so close to the destroyer may have been the "saving" factor in allowing the torpedo to still hit the target.

[Puster Bill]

Well, I used the ruler to measure the distance between the points and it measured the distance as 1. Now can that be interpreted as 1000 meters or 1km?? I'm wondering how close my speed calculation was, i can't have been THAT wrong if the torpedo hit :) But having said that they were not that far away, so being so close to the destroyer may have been the "saving" factor in allowing the torpedo to still hit the target.

Well, first off, 1km is by definition 1,000 meters.

Your speed calculation was fine. You measured the distance travelled in 3 minutes 15 seconds, and the speed was 10 knots. I don't know what extra step you used to get 6 knots, but whatever it was, apparently one of two scenarios came into play:

1. You were close enough that the speed error didn't matter. I doubt this, though for the following reason: At 300 yards a 30 knot torp would take 20 seconds to traverse that distance. A speed error of 4 knots would result in changing the point of impact by about 41 meters, almost half the length of the average destroyer. If you locked on to the center of the destroyer, you would hit it's stern, or completely miss it astern. Since that's the minimum torpedo attack distance, most likely you were farther away.

Using a faster torpedo speed would minimize this error, but even with a T1 at 44 knots, the 20 second/41 meter error at 4 knots distance is still at around 450 meters.



2. An error in your AOB calculation serendipitously counteracted your
error in speed. Hey, sometimes you hit the lottery.

In any case, it's never easy to hit the damned things, so just make your log entry vague enough that Onkel Karl will think it was due to skill, not luck;) Then soak up the glory that comes with hanging a red pennant off your periscope.

[Brag]

Well done. I could never resist a destroyer coming to the slaughter :D

[ddiplock]

Well, I used the ruler to measure the distance between the points and it measured the distance as 1. Now can that be interpreted as 1000 meters or 1km?? I'm wondering how close my speed calculation was, i can't have been THAT wrong if the torpedo hit :) But having said that they were not that far away, so being so close to the destroyer may have been the "saving" factor in allowing the torpedo to still hit the target.

Well, first off, 1km is by definition 1,000 meters.

Your speed calculation was fine. You measured the distance travelled in 3 minutes 15 seconds, and the speed was 10 knots. I don't know what extra step you used to get 6 knots, but whatever it was, apparently one of two scenarios came into play:

1. You were close enough that the speed error didn't matter. I doubt this, though for the following reason: At 300 yards a 30 knot torp would take 20 seconds to traverse that distance. A speed error of 4 knots would result in changing the point of impact by about 41 meters, almost half the length of the average destroyer. If you locked on to the center of the destroyer, you would hit it's stern, or completely miss it astern. Since that's the minimum torpedo attack distance, most likely you were farther away.

Using a faster torpedo speed would minimize this error, but even with a T1 at 44 knots, the 20 second/41 meter error at 4 knots distance is still at around 450 meters.



2. An error in your AOB calculation serendipitously counteracted your
error in speed. Hey, sometimes you hit the lottery.

In any case, it's never easy to hit the damned things, so just make your log entry vague enough that Onkel Karl will think it was due to skill, not luck;) Then soak up the glory that comes with hanging a red pennant off your periscope.

Well, i've been wondering now all this time if i've been using the nomograph correctly. I've now noticed i've not been using the far right column of the graph that lists time in minutes. I've only been using the distance covered and knots scales.....ooops. But ALL my torpedos have still been hitting the ships this way though :-?

Can i ask, is there a quick document somewhere that explains how to use all parts of the nomograph then?? Cause now i've realised i've defo only been using half of it in all my attakcs......and somehow still hitting ships all the time :rock:

[Pisces]

...
Can i ask, is there a quick document somewhere that explains how to use all parts of the nomograph then?? Cause now i've realised i've defo only been using half of it in all my attakcs......and somehow still hitting ships all the time :rock:Just draw a slanted line through any 2 of the 3 numbers you know (time, speed or distance) and then the 3rd number is also crossed through, to match the formula "speed=distance/time". Nothing more to it.

[ddiplock]

Yeah cause i've only been using the distance to work out the speed on the nomograph. When I have the distance, I draw a slanted line to it on the nomograph to work out the speed. But I dont do any markings on the time scale of the graph :-?

that's right isn't it? How else could I be hitting all my targets with the torpedos??

[Puster Bill]

Pisces is right. Nomographs are that simple.

Usually, though, I use either a whiz-wheel like this:

http://img185.imageshack.us/img185/5185/dsc00013ym5.jpg

or a linear slide rule to do my calculations.

I do however have a maneuvering board that I printed out on cardstock, then laminated so that I could use dry erase markers on it, and it has a speed/time/distance nomograph on it. The only problem is that the scale is in yards, not meters! In any case, I very rarely use it anyway. It's very helpful for visualizing the situation, but it's a bit more work than just doing a quick procedure with a wheel or slide rule.

[ddiplock]

Well....I think i've been using it right....how else would I be hitting all my targets doing all the calculations myself?? I must be using it right :)

I'll take a screenie during my next target apprach and show you what i do.

[ddiplock]

Right, as previously stated here is a screenshot of how I have been using the nomograph to calculate targets speed....i haven't yet had any misses using this method, but I get the feeling that from what some people have been saying, my calcs could well indeed actually be off!!

The marks and points on the navmap is for reference only, i'm moving into a firing position on this fat convoy but no solution has been formed in anyway using the figures plotted in this screenie....so here I go:

http://img252.imageshack.us/img252/46/nomo1kh5.th.jpg (http://img252.imageshack.us/my.php?image=nomo1kh5.jpg)

1. Mark the 2 points on the map, wait the usual 3 minutes and measure the distance between them which in this case is only 0.4km.

2. I then look at the nomograph, start at the top of the knot scale, and drag a slant line down to 0.4 on the distance scale. The resulting reading gives a rough speed of about 3.5 knots or so, least that's how I interpret it. Notice I haven't done anything at all with the minutes scale on the nomograph.

Now, please tell me is this method right, close to being right, or totally wrong? I can't imagine it being totally wrong as i've been hitting targets successfully with this method thus far in this career. I'd appreciate feedback from the more experience Kaleuns in using the nomograph to see if I am right. Cheers guys :rock:

[ddiplock]

Thoughts anyone? :)

[kenijaru]

the line should actually "touch" the time between mesurements (in this case... 3 minutes?) and the distance traveled (400metres, right? [0.4 km] ) and then, extend it towards the knots...

I took a traight sheet of paper and used the nomograph on your screen, the target seems to have been moveing at around 5 knots.

is it clear enough? :hmm:

[Abd_von_Mumit]

Yeah yeah, i know what you fellow Kaleuns are going to be saying "you sunk a destroyer, so what? Its hardly the HMS Nelson now is it??" :)

Well you'd be right, its not the mighty battleship Nelson, or any form of large British warship.
No no no, Kapitaen! Sinking a DD is an achievement you can be safely very proud of.

I'd say sinking a battleship is a matter of luck, while sinking DD's is a skill. Well, to be honest, I consider myself a... hmm... seasoned skipper :rotfl:, but I know DD's are too hard to try for me. I just don't do them. I prefer to live through the damn war, let the bulls sink warships, I don't have too. :) In my last two careers I only sunk 2 DD's that were crippled by a storm and were quite defendless.

So I have a large respect to those who dare. :o Keep up the good work and don't let them sink you, so that I can focus on the freighters. :)


1. Mark the 2 points on the map, wait the usual 3 minutes and measure the distance between them which in this case is only 0.4km.

2. I then look at the nomograph, start at the top of the knot scale, and drag a slant line down to 0.4 on the distance scale. The resulting reading gives a rough speed of about 3.5 knots or so, least that's how I interpret it. Notice I haven't done anything at all with the minutes scale on the nomograph.

Now, please tell me is this method right, close to being right, or totally wrong? I can't imagine it being totally wrong as i've been hitting targets successfully with this method thus far in this career. I'd appreciate feedback from the more experience Kaleuns in using the nomograph to see if I am right. Cheers guys :rock:
No, your method is not right.

First, you don't need a nomoograph at all, as you've allready got the speed. A distance in metres between two points in 3 minutes 15 seconds divided by 100 is the speed of a target in knots. In this case distance travelled is 0.4 km (400 metres), so the speed is 4 knots.

Second, the way to use nomograph is different. You always use all the 3 scales. You always need two pieces of information to gather the third needed piece:
- if you got speed and time, you can get distance travelled with that speed in this time,
- if you got speed and distance, you can get time needed to travel that distance given the speed,
- if you got distance and time, you can find the speed needed to travel the distance in the given time.

You do this by drawing a line connecting the two known variables and checkig, where the line intersects on the third scale - the point of intersection is the info you need. The line has to intersect all the scales, so if it's too short, you have to make it longer to reach the third scale.

I know my Ponglish is hard to understand, but If that's too misty, someone will explain it using better words for sure. :up:

[Platapus]

2. An error in your AOB calculation serendipitously counteracted your
error in speed. .


+300 Renown :up: for using the word serendipitously :know:

[ddiplock]

the line should actually "touch" the time between mesurements (in this case... 3 minutes?) and the distance traveled (400metres, right? [0.4 km] ) and then, extend it towards the knots...

I took a traight sheet of paper and used the nomograph on your screen, the target seems to have been moveing at around 5 knots.

is it clear enough? :hmm:

Kind of, dont suppose you could post a screenie showing how you use the nomograph....if you use one at all :)

Cheers Kaleun :up:

[kenijaru]

i guess i coud do some sort of basic drawing, taking as a situation, your screenshot:

http://img252.imageshack.us/my.php?image=nomo1kh5.jpg

he moved 0.4 km in 3 minutes, right?
so:

keep in mind that this edited screen was made in seconds, with a broad line for easy recognition. I paid atention to the way the line should cross the nomograph, but i didnt pay too much atention of to the actual values.

http://img266.imageshack.us/img266/744/nomo1kh5ssna1.jpg (http://imageshack.us)
(http://imageshack.us)

[ddiplock]

so, based on the line you have drawn, the target ship would be doing.....5 knots?? :yep:

[kenijaru]

in that given case, yes, but i didnt use the exact measures, i just wanted to show how it works i wasnt trying to be 100% acurate with the values.

i guess what i'm trying to say is... when you do it, be carefull :yep:

[Pisces]

DDiplock: You must have had an angel inside of your torpedo's gyro mechanism each time because I can't imagine how you managed to succeed doing it your way. I take my hat off for you.

[edit]Yes I can, as Abd_von_Mumit said, since you happend to use the three minute interval the line length happend to match the target speed (roughly, as 0.4km in 3 minutes is 4.3 knots). But any other interval would have you come up with the wrong speed. Whether you actually miss the target depends on alot of other factors too.

As another example of the use of the nomograph take a look at the following link (Paul Wasserman's Manual plotting tutorial; Tip: if you haven't yet allready, read the whole page) The nomograph looks different (horizontal) but works the same way:

http://www.paulwasserman.net/SHIII/#Step 2: Draw a Line Connecting Your Target Distance Traveled and Time Traveled (NG)

[ddiplock]

I guess i'm going to try and stick to firing torps as close as I can, I just did a test fire at two ships in a convoy in my campaign, one of them being at about 1700mtrs away, according to the ruler I used to measure the distance anyway. Torpedos missed on both targets. Naturally I'm going to reload to before firing the torps and "discount" what happend :)


But i'm not 100% convinced on the "multi target" firing explained in the manual. Do you need to relock your periscope onto the 2nd target for the AOB to be auto updated?? Or does it do it automatically when you swing the periscope round? Because after i've input all my data into the TDC manually, I switch it back to "auto" so that it essentially "tracks" the target and updates the solution accordingly.

In convoy training mission, I have yet to successfully hit a 2nd target. I always hit the first, but never the 2nd :damn: :damn:

[Pisces]

When TDC is set to auto, then when turning the scope, only the bearing (obviously) and AOB is updated(to maintain same target course). Range is not. Speed should be the same if it is a convoy/taskforce. Unless they spotted the torpedo wake or something, then they might speed-up. Also if you turn your sub you need to match the AOB to new relative bearing again. Don't know if you did turn. More likely is you missed because of a crude speed setting (3m15 rule is too short to measure fractions of a knot) or wrong AOB. These two are the most important factors in aiming torpedo's. Range is secondary. But targets become smaller the further they are so precise speed and AOB become more important for longer shots.

[Edit]Usually in the heat of battle it is easy to forget to open the torpedo doors. That maybe it?

[ddiplock]

When TDC is set to auto, then when turning the scope, only the bearing (obviously) and AOB is updated(to maintain same target course). Range is not. Speed should be the same if it is a convoy/taskforce. Unless they spotted the torpedo wake or something, then they might speed-up. Also if you turn your sub you need to match the AOB to new relative bearing again. Don't know if you did turn. More likely is you missed because of a crude speed setting (3m15 rule is too short to measure fractions of a knot) or wrong AOB. These two are the most important factors in aiming torpedo's. Range is secondary. But targets become smaller the further they are so precise speed and AOB become more important for longer shots.

[Edit]Usually in the heat of battle it is easy to forget to open the torpedo doors. That maybe it?

Nah I had the torp doors already open, and I never turend my boat either :(

[Pisces]

Then I can only suggest to plot positions over longer periods of time and see how that improves.

[ddiplock]

Then I can only suggest to plot positions over longer periods of time and see how that improves.

Whats best to do? one long timed plot, or several small plots?? Cause i'm sure they'd all just give back the same info as the normal 3 minute plot wouldn't they??

[kenijaru]

you could use the 3:15 mesurement and back it up with a... lets say, 10 minute nomograph mesurement

[Pisces]

I do make plots at multiples of 3:15, but only to find out his general course and speed early. When I know roughly which way he's going I turn parallel or maintain distance and speed up to advance on him. As the plots come in I update the speed setting in the TDC and correct my course based on his course ( if it is taking lon I start a new string of plots after 32:24 (propperly 10x 3:15 interval ) and calculate speed from that. But i'm a weird one when it comes to precision. An average over a couple of 3:15 intervals should make good enough improvements.