Advanced hydrophone techniques.
 

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 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]

Wow. I have to try this out!

Very nice!

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

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.

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.

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.

Wazzoo's Nomograph comes with RUB.

http://www.paulwasserman.net/SHIII/#...he%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.

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.

Kudos, rydster--high marks!

Will have to give it a try. Thanks

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?

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

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.

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