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 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)



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.



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.

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