SUBSIM Radio Room Forums - View Single Post - Calculating position, real course and speed only by hydrophones!

Kubryk · 04-23-09, 05:04 PM

Hi,

this tutorial is what I was looking for. It's simple and well explained. Thanks!

But...
I tried this method 3 times and... I must be doing something incorrectly.

First try:
When my sonarman shouted contact I ordered engine stop. Only when in dead stop (I checked on the map) I took 1st bearing, started stopwatch, after 8 minutes another, after 8 minutes 3rd. Then I started engines again, after 8 minutes since last bearing I took bearing nr 4. Here I paused. I did all calculations required. Angles on triangles p1-m-c1 and m-p2-c2 were close to 90 degrees, so my circles were big.

As you can see on screenshots, I was able to calculate contact's position. I ploted an intercept course. I was really amazed that my guy is shouting 'long range', from my map it looked like the ship is less than 3km from me. After checking with periscope and hydro I surfaced and chased contact with all my speed. He was additional 7km away. It's course was more or less the same as I calculated by hydro-method.

screenshot nr 1

screenshot nr 2

Now I see that I could make mistake - I misplaced P1 with P2. Contact was on my left side, so P1 should be on left side of the helping circle, and I can see I used right end of a diameter as P1. My bad. I'm pretty sure that in other cases I was right though and this mistake is an exception

Second try:
After some time I heared another contact. I sailed towards it, so eventually my crew reported bearing. Again, only when I was in dead stop I started the Mittelwaechter's procedure.

Again, I heard 'long range', so I instantly knew the ship wasn't where it was suppose to be

This time however I tried to estimate. I assumed contact's course-direction is valid, so in order to find him I have to calculate distance between me and contact. I knew it was a merchant. I calculated distance it would travel in 8 and 24 minutes, and using angle calculated with Mittelwaechter's method (29 degrees in this example) I put circles on my map.

This may be confusing, so here's a screenshot:

screenshot nr 3

I assumed - if the contact's speed is constant he would travel x km. I calculated distance for (AFAIR) 5, 6, 7 and 8 knots. I was drawing circles over the protracted angle, aligning circle arrowhead with protractor, so later all I had to do was to put circle over the bearings.

Than I took another bearing, it was 313, 47 degrees to my port.

screenshot nr 4

This bearing line crossed my 4.4 cirlce. Accidentally, it the same spot it crossed the 4th (virtual) bearing to contact I would made if I wouldn't leave my first position.

Anywho, I was already going on perpendicular course. Now funny thing happened. For 14 minutes (game time) bearing to contact was 313 degrees. I was going 8 knots. When my speed changed to 7 (I don't why, I still had juice in batteries) bearing started to change. By this accident I knew two things: contact was doing 8 knots and I really was perpen... our courses would form 90 degrees angle

(maybe if my speed wouldn't drop I would be part of a sea collission?

)

screenshot nr 5

When I saw contact, I plotted it course etc. Turned out it was different than I calculated with hudro and I (my course hasn't change) was no longer perpendicular towards it. The difference between hydro and real course of the contact was ca. 10 degrees.

I sunk the merchant, but was starting to think I cannot use hydro to locate contact with precision. Or - I have badluck and in stock SH3 my merchants are zig-zaging.

screenshot nr 6

3. This gave me a lot to think about. BdU gave me spotted contact on my map. I knew its course (+- 2 degrees). I tried to use hydro-method for the third time.

Again, from my calculations I learned that contact should be very close to me
. I didn't bother to mark that place on my map.

Those two small circles you can see on screenshot represents contact position marked by periscope observation. Note that real course of the contact was true to BdU report and was ca. 10 degrees off than my hydro calculations. BdU was right, not me.

screenshot nr 7

screenshot nr 8

Now to questions: what can be wrong? I'm 100% positive there's nothing wrong with my bearing. I can put things like that on my map. There's nothing wrong with my helping circle (except for example 1). I often pause the game to draw everything as perfect as possible. So?

I noticed one thing - the biggest challenge for me is to draw a 'virtual' bearing, one I would have made if I didn't start engines after initial 3 bearings. My problem is I'm having hard time judging distance. When I use angle calculated from helping circle (giving me course-direction) distance between 1-2 and 2-3 bearing are different. Eg. it's 2km in first 8 minutes, but 1,8km in the second. So how can I put that 'virual' bearing correctly? In your example Mittelwaechter you seem to use circle with radius = distance between 2nd and 3rd bearing. But in your picture this is the same as between 1st and 2nd.

Can anyone help me?

Sorry for suprisingly long post

Kubryk

PS
I don't know how to put clickable thumbnails hence the link under every picture.

04-23-09, 05:04 PM	#9
Kubryk Bosun Join Date: Apr 2009 Location: Warsaw, Poland Posts: 66 Downloads: 53 Uploads: 0	Hi, this tutorial is what I was looking for. It's simple and well explained. Thanks! But... I tried this method 3 times and... I must be doing something incorrectly. First try: When my sonarman shouted contact I ordered engine stop. Only when in dead stop (I checked on the map) I took 1st bearing, started stopwatch, after 8 minutes another, after 8 minutes 3rd. Then I started engines again, after 8 minutes since last bearing I took bearing nr 4. Here I paused. I did all calculations required. Angles on triangles p1-m-c1 and m-p2-c2 were close to 90 degrees, so my circles were big. As you can see on screenshots, I was able to calculate contact's position. I ploted an intercept course. I was really amazed that my guy is shouting 'long range', from my map it looked like the ship is less than 3km from me. After checking with periscope and hydro I surfaced and chased contact with all my speed. He was additional 7km away. It's course was more or less the same as I calculated by hydro-method. screenshot nr 1 screenshot nr 2 Now I see that I could make mistake - I misplaced P1 with P2. Contact was on my left side, so P1 should be on left side of the helping circle, and I can see I used right end of a diameter as P1. My bad. I'm pretty sure that in other cases I was right though and this mistake is an exception Second try: After some time I heared another contact. I sailed towards it, so eventually my crew reported bearing. Again, only when I was in dead stop I started the Mittelwaechter's procedure. Again, I heard 'long range', so I instantly knew the ship wasn't where it was suppose to be This time however I tried to estimate. I assumed contact's course-direction is valid, so in order to find him I have to calculate distance between me and contact. I knew it was a merchant. I calculated distance it would travel in 8 and 24 minutes, and using angle calculated with Mittelwaechter's method (29 degrees in this example) I put circles on my map. This may be confusing, so here's a screenshot: screenshot nr 3 I assumed - if the contact's speed is constant he would travel x km. I calculated distance for (AFAIR) 5, 6, 7 and 8 knots. I was drawing circles over the protracted angle, aligning circle arrowhead with protractor, so later all I had to do was to put circle over the bearings. Than I took another bearing, it was 313, 47 degrees to my port. screenshot nr 4 This bearing line crossed my 4.4 cirlce. Accidentally, it the same spot it crossed the 4th (virtual) bearing to contact I would made if I wouldn't leave my first position. Anywho, I was already going on perpendicular course. Now funny thing happened. For 14 minutes (game time) bearing to contact was 313 degrees. I was going 8 knots. When my speed changed to 7 (I don't why, I still had juice in batteries) bearing started to change. By this accident I knew two things: contact was doing 8 knots and I really was perpen... our courses would form 90 degrees angle (maybe if my speed wouldn't drop I would be part of a sea collission? ) screenshot nr 5 When I saw contact, I plotted it course etc. Turned out it was different than I calculated with hudro and I (my course hasn't change) was no longer perpendicular towards it. The difference between hydro and real course of the contact was ca. 10 degrees. I sunk the merchant, but was starting to think I cannot use hydro to locate contact with precision. Or - I have badluck and in stock SH3 my merchants are zig-zaging. screenshot nr 6 3. This gave me a lot to think about. BdU gave me spotted contact on my map. I knew its course (+- 2 degrees). I tried to use hydro-method for the third time. Again, from my calculations I learned that contact should be very close to me . I didn't bother to mark that place on my map. Those two small circles you can see on screenshot represents contact position marked by periscope observation. Note that real course of the contact was true to BdU report and was ca. 10 degrees off than my hydro calculations. BdU was right, not me. screenshot nr 7 screenshot nr 8 Now to questions: what can be wrong? I'm 100% positive there's nothing wrong with my bearing. I can put things like that on my map. There's nothing wrong with my helping circle (except for example 1). I often pause the game to draw everything as perfect as possible. So? I noticed one thing - the biggest challenge for me is to draw a 'virtual' bearing, one I would have made if I didn't start engines after initial 3 bearings. My problem is I'm having hard time judging distance. When I use angle calculated from helping circle (giving me course-direction) distance between 1-2 and 2-3 bearing are different. Eg. it's 2km in first 8 minutes, but 1,8km in the second. So how can I put that 'virual' bearing correctly? In your example Mittelwaechter you seem to use circle with radius = distance between 2nd and 3rd bearing. But in your picture this is the same as between 1st and 2nd. Can anyone help me? Sorry for suprisingly long post Kubryk PS I don't know how to put clickable thumbnails hence the link under every picture.