Calculating position, real course and speed only by hydrophones!

[Mittelwaechter]

Hi Kubryk,

nice to see you are working on this, you are doing a good job there!

Whenever the angle between first and second bearing is small, add a few minutes and ask for the second bearing again to reduce error probability.

The bearing of the hydrophone operator is a cone. In 20 km distance the bearing covers a width of ~ 350 meters (2r pi /360)
The SH3 map tools are not designed to do these 'hydrohunt' calculations.
Try to center the bearingline in the 350 meter cone.

The best way to calculate the virtual bearing is by dividing the complete distance travelled on coursedirection and add the average.

After third bearing estimate the virtual bearing and try to achieve a big angle for the fourth bearing. You may want to surface and go flank for some minutes. Start immediately and do the calculations while sailing.
Try to come to a full stop before asking for the fourth bearing.
Make sure to follow your U-boats coursepath and try to work the fourth bearing exactly.

I have no idea what's going on, but checking your screenshots the initial contact would have been in ~ 5 km distance - according to your fourth bearing and the resulting real courseline. Your hydro operator is not that bad.

There is allways a difference between the real courseline and the calculated courseline, due to the map tools limitations - but it is small enough to still get a proper target solution. Even the distance is irrelevant as long as you head perpendicular to the courseline.

Try to 'correct' the weapons officers perfect settings and change the AOB for +/-10° - you'll still score a hit. Change the distance - Pythagoras will give you a smile.
The real source of error would be the contact speed. But if you want, you can calculate the speed from the complete travelled distance!
(timestamp the initial contact report... - or keep on restarting the stopwatch...)

The more you close in to your contact, the more error tolerant your setup.
Well, this all requires an exact 'cross bearing' to get your real contact position.

Have fun!


Edit: your conclusion about same speed is correct (your 8 knots story), but the assumption of a perpendicular course is not consequently correct.

[Kubryk]

Thanks for your reply! I noticed that small angle difference between bearings is somewhat inconvenient, still I'm worried that target would escape. It happened once, I took two bearings but third one I had to do manually, sonarman no longer could hear him. I will try to make that distance bigger though.

I try to accomplish two things thanks to your tutorial - it would be nice to know target's course just by hearing, and I would really like to sink at least one ship while submerged and without periscope. Must be a great feeling

I didn't know that bearing is a cone 350m wide, thanks for that info. I always try to center things, must be something wrong with my brain (I don't use this rule in photography, thank God )

I did all my calculations sumberged. I will surface after 3rd bearing and go flank, we'll see if it's going to help. Thanks for the tip!

Originally Posted by Mittelwaechter

There is allways a difference between the real courseline and the calculated courseline, due to the map tools limitations - but it is small enough to still get a proper target solution. Even the distance is irrelevant as long as you head perpendicular to the courseline.

I've been meaning to ask about this, I read that sort of statement a lot on subsim. How is it possible that distance doesn't really matter as long as you have speed and AOB correct? I don't get it, it's against my intuition

Originally Posted by Mittelwaechter

Try to 'correct' the weapons officers perfect settings and change the AOB for +/-10° - you'll still score a hit. Change the distance - Pythagoras will give you a smile.

I only use weapons officer to see how long till loading a tube, I'm my own weapons officer for calculating firing solutions

Originally Posted by Mittelwaechter

your conclusion about same speed is correct (your 8 knots story), but the assumption of a perpendicular course is not consequently correct.

I don't have a ruler on me so I will ask - same speed means same bearing ALWAYS? No matter how courses are related to each other?

It's true with parallel and perpendicular for sure, hm... maybe it's true always... no. It can't be.

[Pisces]

Originally Posted by Kubryk

Thanks for your reply! I noticed that small angle difference between bearings is somewhat inconvenient, still I'm worried that target would escape. It happened once, I took two bearings but third one I had to do manually, sonarman no longer could hear him. I will try to make that distance bigger though.

The hydro-man only starts calling out within 20km or so (or was it 25km?). But you can hear upto 34km. That range is 70% bigger, and almost 3 times the area of 20km range. At the bearing where the contact has an AOB of 90 degrees it only halve-way through your hydrophone range. So there is usually plenty of time before you really loose it. Unless it happends to be very near the extreme end of the range. Oh well, can't have everything.

Listening yourselve for the soundbeam-sides where the sounds die out is tricky. You do loose a bit of bearing accuracy that way. But listening for maximum volume at the middle bearing is VERY tricky. Then bigger bearing differences are a must.

Use the smaller bearing difference drawing to estimate how much time there is before it is near 90 degree AOB, or it leaves hydrophone range (if you don't mind catching up to it later). Remember, speed of contact is constant, so any distance it has moved along the course is proportional to time between bearings. Then use halve of the time available as the new interval (but be conservative as it is very crude). Or use the old 3rd bearing as the new 2nd bearing if that 1st new interval has allready past, and double the interval before taking the new 3rd bearing. The 3rd bearing doesn't have to end up at 90 degree AOB. It just a way to not fall behind.

But you must be suffering from information overload now. I'll let you digest it first. And alcohol doesn't help.

[Mittelwaechter]

Well, Herr Kaleun, your Navigator Konrad Schlumberger has been asigned to command his own U-Boot.
But during the last shoreleave Heinz Voigt - your hydrophone operator - visited the new hydrophone operator seminar at the U-Boot school in Kiel.

He came back with some great skills to support you in hunting contacts only with hydrophne.
He is able to calculate most of the tricky stuff to get the real courseline of an inbound contact under those conditions where the initial angles between the first three bearings are small. It indicates the contact is sailing along a course coming close to your position.

Heinz will give you constant reports of the bearings, including the information whether the contact is closing in or whether it sails in constant distance.
At the bearing this information changes, the AOB of the incoming contact is 60° (!).

Additionally Heinz reports proper distance statements and tells you if the contact is far away or at medium distance.

Whatever occurs first - note its bearing on the map. Draw a circle to represent the medium distance around your U-Boot.

(please someone provides the information what distance is medium in GWX - I changed my settings in Contact.cfg and didn't back up! I guess it was 8000 meters, but I'm not sure.)

At the time you have both informations, copy the courseline of the 60° AOB to the "medium distance" bearing at the point it intersects the medium circle.

You may want to change your position if the 60° AOB information comes first, of course heading perpendicular to the "courseline", to ensure the contact will cross your medium distance circle.

Well, the rest should be easy...

[Pisces]

Originally Posted by Mittelwaechter

....
(please someone provides the information what distance is medium in GWX - I changed my settings in Contact.cfg and didn't back up! I guess it was 8000 meters, but I'm not sure.)...

Correct. S/M/L=1km/8km/16km. (for GWX 2.1, but must be the same for 3 aswel)