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View Full Version : How to determine target course with Hydrophone.



the_rydster
08-30-2005, 03:39 AM
If the conditions are poor and/or you are out of visual range all you have is the hydrophone (pre sonar times anyway!). Normally people use this as a rough guide. We can do a little better though.

You need to check out the 'Sound trainer' so you know how to determine a ships speed just from the frequency of the screw noise.

First of all take a hydrophone bearing and start the stopwatch. Now work out the speed (actually you can do this first of you want). It is simpler to wait a multiple of 3 mins 15 secs before the next bearing is noted (in the example below I waited just the 3 mins 15 secs but if the target is significantly far it would be best for accuracy to wait 2 or 3 time this), wait this period of time and note the new bearing, then wait the same period of time again and note the new bearings. Be aware if the target has got further way just from the sound also.

Now assuming the target has kept a constant bearing and speed you can do some stuff on the map. Plot the three bearings as lines (using the ruler), and create a circle with a radius equal to the distance the ships should have travelled between each bearing sample (easy if you stick to 3 min 15 sec multiples).

Now you move this circle so its centre is on the middle line (your second bearing). You can now slide it up and down this line untill its is at the desired place. This desired place is where the circle touches the first and third bearings and a straight line will connect the points where the circle contacts the first line with the middle of the circle, and the point where the circle contacts the third line. This can be a little tricky and the GUI is not really designed to do this. A tool would be usefull.

You will know have the ships course and incidentaly three ranges.

I would have posted images but it needs a URL so I was not able to.

Messervy
08-30-2005, 04:41 AM
Brilliant stuff. Excellent work. http://forums.ubi.com/images/smilies/25.gif

You may open an account here: http://www.pbase.com/register

MBeck
08-30-2005, 05:20 AM
Any chance for a guide with visual aid?

the_rydster
08-30-2005, 05:45 AM
Ok I am working on getting some images posted.

This method is kind of fiddly but I will work on it a bit more.

CRSutton
08-30-2005, 10:27 AM
thanks

the_rydster
08-30-2005, 10:41 AM
If you check out the 'Sound tutorial' you will learn that it is possible to determine a ships speed with precision.

Using this method (which appears to work so far!) you can therfore track a target and torpedo it without using the periscope/UZO (Note in the 'Sound tutorial' they show you how to do this but the method detailed there requires the targets course to be at 90/270 to you which is not always the case)

It is probably easier to work out the speed first. How you ID the target is up to you, I kind of think that a superior hydrophone guy could ID it from the sound, although I am not sure if this is possible in SH3.

Once you have the speed take three bearings to the target. As I mentioned it is easiest to take advantage of the 3 min rule but so long as you work out the distance the target should have travelled between each bearing, and you use the same time interval between the second and third bearings it is ok.

In the example below I took three bearings at intervals of 3 mins and 15 secs. One problem with the tools is that this is a pain to plot. The cool bearing mod does not work on my ATI hardware so this is the best I could do http://forums.ubi.com/images/smilies/16x16_smiley-sad.gif

http://www.pbase.com/image/48457455

After my last bearing I reset the stopwatch (this is only important if you want to torpedo the target).

I hope this diagram below makes some sense! http://forums.ubi.com/images/smilies/16x16_smiley-surprised.gif . Basically you create a circle whose diameter equals the distance the target should have travelled between each bearing (we have already worked out the speed already so this should be easy!). The target we assume has travelled in a straight line. The target has travelled from a point on the edge of this circle to the middle and to a point 180 deg away from the first point (to the opposite side of the circle). So if we place the middle of the circle on the middle line and move it up and down untill you can draw a straight line from where it touches the first bearing line, to the middle, and right on through to the third beaing line. This procedure takes a bit of 'eyeballing' really. If your bearings were poor quality to will find out here as it will not fit properly.

http://www.pbase.com/the_rydster/image/48457459

We now know the target course and last range so we can extrapolate. In the example below I set up to TDC without raising the periscope. It was easy to set up the TDC for a bearing of zero (this is the lazy way!). I worked out the AOB in advance (thanks to the cool wheel) and the range to target and set everthing up. I measured the distance the target still had to travel from its last known point to where it crossed by bow (zero deg). Using the cool slide rule thing we can estimate how long it will take the vessel to complete this distance (we know the speed of course!). Having already started my stopwatch, I can kick back, after setting my torpedo running depth etc and wait for the time to expire.

Then I fire a 5 degree 4 tube spread to be sure.!

http://www.pbase.com/the_rydster/image/48457532

This method is no way as good as visual targeting and is probably more use for tracking targets at extreme range or in adverse conditions. Convoys are not so easy since there are multiple noise contacts. Another thing is that it is dependant upon accurate very bearings from the hydrophone and this is not helped by having no stopwatch in the sonar room (you need a real one). I do not know how currents and wind is modelled into the game so screw rpms may not always result in equivilant speed.

Hope this made some sense! http://forums.ubi.com/groupee_common/emoticons/icon_cool.gif

the_rydster
08-30-2005, 11:09 AM
Arrrgggghhh!!

http://img5.picsplace.to/img5/2/First_Image_000.jpg http://img5.picsplace.to/img5/2/Second_Image_000.jpg http://img5.picsplace.to/img5/2/Third_Image_000.jpg http://img5.picsplace.to/img5/2/Destroyed_000.jpg

the_rydster
08-30-2005, 12:27 PM
I forgot to mention that you can just use the hydrophone to track your target to the desired torpedo firing bearing.

The method is really about determining course and range.

Firing torpedos blind based on an extrapolation is just a party piece really. Far more sensible to continue to use the hydrophone after the third bearing (and subsequent course and range calculation). Then you can chuck the periscope away for good!