Advanced hydrophone techniques.

[the_rydster]

I posted this on the official site yesterday but it was a bit...well er...rushed so here it is again.

Anyone who has checked out the cool sound trainer (http://www.subsim.com/subsim_files/patches.html) will know that you can work out a targets speed just by the frequency of the noise from the screws.

In the sound trainer tutorial they demonstrate that knowing the speed of the target allows you do do all your targeting and firing just using the hydrophone. However the target must be on a 90/270 degree course with respect to your boat for the method to work.

Using the hydrophone we can be a little more devious. First work out the targets speed, then take a hydrophone bearing, using a stopwatch wait a period of time (I use multiples of 3 min 15 secs to make it easier later on), and take another bearing, now wait the same time interval as before and take a third and final bearing.

There will know be three lines on the map (at bit of a pain to draw actually)

http://img5.picsplace.to/img5/2/First_Image_000.jpg

Knowing the target speed, and the time interval used, work out how far the target travelled between each bearing survey (easy if you use the 3 mins 15 secs thingy). Now create a circle with a radius equal to this distance. Now move this circle so that the centre is somewhere on the middle line. Slide the circle up and down this middle line untill you can connect the point where the circle contacts the first bearing line, with the middle of the circle, and through to the point where the circle contact the third bearing line, using a dead straight line.

http://img5.picsplace.to/img5/2/Second_Image_000.jpg

If your timings or your bearings were inaccurate it will not fit properly of your results will be erroneous. Making the circle fit can be a little tricky and you have to really 'eyeball' it, just remember that the circle represents an infinite (360 in practice) number of target course bearings, and that the target (we assume) has to travel in a straight line, the length of which we all ready know, it thus has to go through the centre of the circle. Be aware if the target has got closer or further way based on the sound also.

We know have a target course, and the range and bearings of three known positions in space and time. We are able to extrapolate and use this data to intercept (if the target is at great distance) or line up a torpedo shots (if it is near) As mentioned in the sound tutorial all the shooting of torps can be done using the hydrophone. The TDC can be configured manually for a future shot. Using this method we can work out AOB and range in advance, or navigate so AOB is 90 and use the tables in the sound tutorial.

http://img5.picsplace.to/img5/2/Third_Image_000.jpg[/img][/url]

[Twelvefield]

Wow. I have to try this out!

[Saintaw]

Very nice!

(And I have to know what those lines at the bottom are, and what they are for???)

[Charos]

Yes easy isnt it - and much more challanging than just pressing the fire button. :up:

The conversion tables on the bottom are the larger version of a mod that coverts Knots to KM to distance travelled in Minutes, If you know target speed in Knots for instance you can work out how many Kilometres the target will travel in 10 Minutes by drawing a line between the two values you know to obtain the third unknown.


I use this as well as a EXCEL spreadsheet with all the values up to 44 Knots ploted.

[the_rydster]

Yeah spot on about the lines at the bottom. I forgot which clever person made that overlay.

As the cool people who made the sound trainer pointed out you can do all your firing from the sound room (which is great if conditions are terrible or there are eyes looking out for your periscope).

This method takes it a step futher and we can now calculate courses, bearings, ranges just from sound

One flaw of the sound tutorial method is that it is hard to line yourself up to the desired AOB without using the periscope. Now we can as we know the target course. We can still use the tables but as we can now extrapolate range we can manually configure the TDC if we want as well.

[Sawdust]

Pretty neat trick.

I guess you are using the circle to determine the range of the target at each of the three bearing surveys.

When I play with map updates on, the hydrophone results shows both bearing and distance...do you not get a distance reading the the hydrophone without map updates?
If not, can you eventually learn the distance to a target by the volume of the sound of its propellers?

[Charos]

Pretty neat trick.

I guess you are using the circle to determine the range of the target at each of the three bearing surveys.

When I play with map updates on, the hydrophone results shows both bearing and distance...do you not get a distance reading the the hydrophone without map updates?
If not, can you eventually learn the distance to a target by the volume of the sound of its propellers?


The circle is merely a geometrical tool to connect all three bearing time stamps based on the fact that the Target is travelling in a straight line and at a constant speed.

The Vector representing the Ships course and speed bisects the circle and where it interescts each bearing measurement provides you with the distance from your U-Boat at any time between these bearings.
If this line is then projected beyond those bearings it represents a position the Target will be in the future.

The Vector that represents the target vessel simply falls between the three measured bearings and because (in this case) we have used time stamps for each bearing that are equally spaced a circle can be used as the outer bearings can be aligned tangentially to the circle.

In fact you can use Bearings with any timestamp you wish if you have an idea of the target speed.

[Twelvefield]

Wazzoo's Nomograph comes with RUB.

http://www.paulwasserman.net/SHIII/#Section%20VI%20-%20Advanced%20Speed%20Calculation%20-%20Using%20the%20Nomograph

There's a link to download the nomograph (the thing with the lines) outside of RUB, as well as his superlative tutorials on how to use this simple and effective tool.

[the_rydster]

The circle is merely a geometrical tool to connect all three bearing time stamps based on the fact that the Target is travelling in a straight line and at a constant speed.

The Vector representing the Ships course and speed bisects the circle and where it interescts each bearing measurement provides you with the distance from your U-Boat at any time between these bearings.
If this line is then projected beyond those bearings it represents a position the Target will be in the future.

The Vector that represents the target vessel simply falls between the three measured bearings and because (in this case) we have used time stamps for each bearing that are equally spaced a circle can be used as the outer bearings can be aligned tangentially to the circle.

In fact you can use Bearings with any timestamp you wish if you have an idea of the target speed.

Yeah that is about right. The circle represents all the potential vector solutions for the target given that we know its speed already. We have time stamped bearings so all we have to do is move the circle to the right place to find that solution.

[don1reed]

Kudos, rydster--high marks!

[SmokinTep]

Will have to give it a try. Thanks

[Trav_R]

There's no way to tell speed by RPM alone though right? You still need a visual ID. So, you'd at least have to pop up the periscope once I believe wouldn't you?

[HEMISENT]

Trav_r
Theres a chart out made by GreyRider & Capt Nautilus. It gives the speed of all the merchants by counting prop rpm.

[Trav_R]

Yeah but you still need a visual ID to see what ship it is before you can convert RPM to speed. I was asking if it were possible to tell purely by sound, but I doubt it.

[zombiewolf]

:|\ Phew. Thank goodness I have a fantastic Weapons Officer :yep:
Thats pretty intense :o

[greyrider]

i just want to add to this post guys to let you know that if your using the bearing speed charts and the rpm charts to attack ships, that there are a couple of other attributes to those charts that you should know, and i will list them below.

1. the bearing speed charts are visual, meaning you can use the periscope to shoot also.

situation: you see a t-3 closing, and your in a good 90 decree to his course, from the rpm charts his turn count is 34 rpm, the t-3 is traveling at 11 knots.

now the bearing speed chart states that a ship traveling at 11 knots across the bow, using the bow torpedoes to engage it the firing bearing will be either 14 decrees or 346, depending on which way he is closing on you.

lets say the t-3 is closing from the starboard side, that means the firing bearing will be 14 decrees. preset the periscope to 14 decrees, watch the ship travel to the firing bearing of 14 decrees and when his funnel is at bearing 14, fire!

the only time i use the hydrophone now to fire is if i cant see the ship. if i can see the ship i use the periscope with the rpm charts and the speed bearing charts.


2. you can use the bearing speed charts and rpm charts on the move, meaning you dont have to be stationary to fire, you can close on the target. this is about as close to a fire and forget as i can get.

3. once you know what the target and its speed is, you can manually input the bearings and speed from the charts into the tdc and fire like that.

4 the bearing speed charts are also radar bearings to fire at to.


so the bearing speed charts can be used:

visually in the periscope,
by sound in the hydrophones,
using radar to engage the target,
manual tdc input.

i have developed a sonar overlay mod that i would like to see up to the community, i cant mod it, i dont know how to do that, but i can build one on the map if theres an interest ill post pictures and then if it can be modded then any modder is welcome to mod it.

[Trav_R]

I know what you're saying, but the whole idea of firing just using the hydrophone has sort of a paradox. The big benefit of using the hydrophone to manually fire is that you can use it without seeing the target. The problem with this is you don't know the target's speed unless you've actually seen the target to ID it. So, if you've seen the target and were in a position to strike, why bother with the hydrophone? It's biggest benefit is almost perfectly cancelled by its weakness. If you have enough information about the target to get on a perpendicular course with it and close to its path, then you have enough information to manually set up the TDC and fire visually. Even if it's heavy fog, you can still see up to about 400m and with careful hydrophone work you can work yourself into that position without too much difficulty.

Although it may be slightly easier to just point your optics at the correct bearing and fire when the target reaches it (assuming you know his speed accurately), you're taking a chance on hitting the target in one of its strong areas and not doing much damage to it. Even in heavy fog, I'd rather just wait till I can see him and them aim for his fuel bunker/engine room. I'd like to use this hydrophone method but the whole idea of having to see the target first kind of makes it pointless as far as I can tell.

[joea]

Well didn't the USN try before the war to use the hydrophone only for submerged torpedo attacks? It didn't work out apparently...(neither did their torps for the first part of the war).

[JohnnyPotPie]

BRAVO SIR BRAVO!!! :rock:

[Canovaro]

Thank you for pointing out how to figure out the target's course!
I'm sure I will you this a lot!
:up:


Anyway about ID'ing the target to figure out speed as discussed above, You don't have to do this in a reported convoy, because the speed is given in the report. In any other case, you're right, except when you use Greyrider's method, which is of course a bit unrealistic.

You can also guess what it is by the sound type and frequency :)

Sorry for bringing up an old thread, but it's a good one isn't it?

[Canovaro]

I did some testing while on patrol.
East coast of England, I heard a warship, my hydro man said it was moving "schnell".
I figured that would be something between 20 and 30 kts, so I tryed the stuff of the_rydster, at the top of this thread.

I let the sonar man report the target bearing, noted my own bearing, and turned on the timer.
After 3 minutes and 15 seconds I let the sonar men report again and noted my own bearing.
After another 3 minutes and 15 seconds I let the sonar men report again noted my own bearing.

I figured out the absolute target bearing by doing "relative target bearing" + "own bearing" for all three observations.

Now I had three bearings:
A: 28+134=162
B: 35+134=169
C: 46+134=180

Below you see the corresponding lines I made.
I also made a circle with a span of 2 km to each side.
I moved the circle over the three line untill I had a straight line through the point where the circle cut line A and C, and where the center of the circle was in the middle.
I made a new line through these three points.
Then I made another circle of 3 km to each side and did the same thing.

If my guess about the speed being between 20 kts and 30 kts was right , the ship's track should be between line D and E.

(the speed turned out te be 27 kts in a radio message that came in later)
Anyway I never had the need to go after it since 27 kts was way to fast.


http://kuijperonline.nl/weblink/hydro2.jpg

[Canovaro]

Wait a minute, that ain't right.

I draw 2km and 3km circles. For a 20-30 kts speed that shoud have been 20 and 30 km.
If that warship was sailing between 2 and 3 kts, the drawing should have been right.

Bernaaard! :rotfl:

[TteFAboB]

It's possible to fire indeed with no data other than the hydrophone, especially if you get a nomograph or make one yourself, but I can't score consistently on the small merchants. I stopped firing at the smaller merchants to avoid wasting fishes and also because I'm tired of lying to my crew: "No good men, that one was another dud..."

I've managed to score hits on the large vessels though. The tough part is judging speed because the damn ruler has that 50m margin of error and also setting a precise 90 degree heading.

[Mittelwaechter]

Hitting targets >>without<< visual data?

http://www.subsim.com/radioroom/showthread.php?t=110619&highlight=mittelwaechter

There's a tutorial-clip available - scroll down.

:D