Four bearings method... range error 4 km?

[Shkval]

I'm sitting at 25 m in channel between England and Ireland... terrible weather, zero visibility... and finally after 5 days of silence and a few patrol crafts - a merchant contact! Nice and straight... routine plotting... course 108... triangulation... (moved sub about 1.5 km from original point, at 8 knots flank submerged)... range 8 km...speed 9 knots... again flank speed submerged to get in 1 km firing range position... got there...brake... and wait... wait... wait... merchant bearing 348 - salvo Los (zero gyro angle)! Then jump to free camera and follow trails... and follow... and follow... and follow... wait a minute, this takes too long... finally shadow in the fog there he is! But my torpedoes died... it turns out that range was at least 4 km wrong! :huh:
I'm not bragging... but I became really good at hydrophone plotting, I even prefer it to optical approach... solution was PERFECT... is this some bug? Has anyone had same situation?

One more thing has anyone encountered some kind of "light beacon" ship? It has no flags... it is not in recognition manual... periscope won't lock it...

[VONHARRIS]

One more thing has anyone encountered some kind of "light beacon" ship? It has no flags... it is not in recognition manual... periscope won't lock it...

Yes there are plenty of these "lightships". They are listed as enviromental objects and this is why there is always a tugboat or a small coastal vessel next to them.
You can not lock on them.
I don't know if you can fire upon them but it wouldn't make sence.

[Pisces]

I'm sitting at 25 m in channel between England and Ireland... terrible weather, zero visibility... and finally after 5 days of silence and a few patrol crafts - a merchant contact! Nice and straight... routine plotting... course 108... triangulation... (moved sub about 1.5 km from original point, at 8 knots flank submerged)... range 8 km...speed 9 knots... again flank speed submerged to get in 1 km firing range position... got there...brake... and wait... wait... wait... merchant bearing 348 - salvo Los (zero gyro angle)! Then jump to free camera and follow trails... and follow... and follow... and follow... wait a minute, this takes too long... finally shadow in the fog there he is! But my torpedoes died... it turns out that range was at least 4 km wrong! :huh:
I'm not bragging... but I became really good at hydrophone plotting, I even prefer it to optical approach... solution was PERFECT... is this some bug? Has anyone had same situation?
...
Your description of the events is to crude to say anything about the reasons why the actual range was further out. You have to paint a better picture of the bearing lines, how much time was in between the events. That sort of thing. Probably something went wrong during drawing the bearing/course plot. (how can you determine if plotting was routine, or the solution was perfect? You'd have to cheat to know that.) Or it changed course at some time because the next waypoint was due. That's allways a possibility.

[Feld Grau]

Yes there are plenty of these "lightships". They are listed as enviromental objects and this is why there is always a tugboat or a small coastal vessel next to them.
You can not lock on them.
I don't know if you can fire upon them but it wouldn't make sence.


I once was on the East Coast of England and found one of these in the approach to a harbor. It was stormy,i had had no contacts for about a week,and figured I might as well attack this merchant ship my WO refused to acknowledge existed. 4 torpedoes and 12 hours later,it was still afloat(although burning),the trawler next to it had spotted me,and somehow I either hit a mine or coastal artillery whacked my sub and killed my entire watch crew. Limped back to base,but it was one of the most peculiar events that has happened to me in SH III.

[Sailor Steve]

Lightships, like lighthouses, were a boon to all sailors at sea, and were strictly off limits to all attacks.

[Shkval]

Well time between bearings was 10 minutes, nice bearing rate... as far as I remember 6 - 7 - 9 degrees difference between them, not too close to each other, the only thing I'm suspicious about right now is triangulation point ... is 1,5 km from first position far enough? I didn't surfaced because I don't like to loose contact...

[Pisces]

...
the only thing I'm suspicious about right now is triangulation point ... is 1,5 km from first position far enough? I didn't surfaced because I don't like to loose contact...It depends in which direction it was. If it was roughly in a direction along the bearing lines then it didn't help much. Ideally you would run to the second position parallel to the target course. This prevents the target from overtaking you as much as possible. (or delays it if inevitable by his possibly superior speed) The relative motion is the least in his favour in this direction. And you also should get a nice crossing of the virtual 4th bearing line and the real 4th bearing line.

Driving to a 90 degree across target course immediately is a risky gamble. You don't know his speed or distance yet, so he might safely pass by infront of you, being to late to fire at him in time.

Once you have an idea of his speed and range then you can make the choice if you want to close the distance (pure intercept), intercept to a 90 degree attack position somewhere forward, or give up entirely. Atleast you know alot more about him, and you gave up the least amount of your position at worst. You still have the option to move out of detection range (go perpendicular away from his course until safe to surface) and do a surfaced run around ahead. With the former option you could end up deep in his rear quarter and the run around would take much longer with more risk of detection.

[Shkval]

Ideally you would run to the second position parallel to the target course. This prevents the target from overtaking you as much as possible. (or delays it if inevitable by his possibly superior speed) The relative motion is the least in his favour in this direction. And you also should get a nice crossing of the virtual 4th bearing line and the real 4th bearing line.

Exactly!! Well you was one of my teachers... :salute: ...My submerged "sprint" was perpendicular to the "fourth" i.e "predicted" bearing... almost at the same course... bearing rate changed for only one degree and triangulation bearing was kinda shallow-ish but I thought it was an effect of contacts speed...it turns out to be 9 knots, and my max submerged is 8... is this the mistake? Or did he just changed course in the meantime?

[Hangman]

Yes there are plenty of these "lightships". They are listed as enviromental objects and this is why there is always a tugboat or a small coastal vessel next to them.
You can not lock on them.
I don't know if you can fire upon them but it wouldn't make sence.

I once was on the East Coast of England and found one of these in the approach to a harbor. It was stormy,i had had no contacts for about a week,and figured I might as well attack this merchant ship my WO refused to acknowledge existed. 4 torpedoes and 12 hours later,it was still afloat(although burning),the trawler next to it had spotted me,and somehow I either hit a mine or coastal artillery whacked my sub and killed my entire watch crew. Limped back to base,but it was one of the most peculiar events that has happened to me in SH III.

Lightships, like lighthouses, were a boon to all sailors at sea, and were strictly off limits to all attacks.

Well, ... call me cursed!

It was the end of November in the North Sea. The skies were overcast and the sun was about to set when I came across a nice juicy merchant. I got myself into position and waited for the sun to set and the merchant to arrive. I had it timed to hit him just at sundown. I was about five minutes away from gaining another notch in my count when an ASW trawler and a destroyer rang up on the Hydrophones, coming directly at me. I punched it into flank and crossed the path of the merchant for a tail shot while simultaniously getting out of the way of the two warships. I had about 20 minutes before they came into viewable range and I needed only two to sink this merchant now.
The eel ran hot, straight, and normal for a nice 90 deg impact low on the hull, but the merchant was over 9k tons and the eel simply disabled her. The destroyer and trawler were moving faster than my initial calculations and I discovered I had less than eight minutes to sink this merchant before the DD would be in viewable range. I surfaced and called immediately for crew to the deck gun.
As I watched from the bridge as my crew put holes in the side of the merchant, I saw off in the distance a light, somewhat obscured by the merchants flaming smoke screen.
The DD arrived and fired a shell over my bow just as the merchant gave in and I rapidly made my decent to 40 meters. Again, I hit flank speed and turned directly for the DD and the trawler. I skirted away without a single DC near me, but it took a good hour before they gave up the search.
The light in the distance made no noise by the hydrophones so I had to search it out on the bridge. The night had become extremely dark and overcast so the light ship was easy to fix. I approached it cautiously not knowing what it was (I'd heard later in the tavern it was a party ship) but it made no movement to go dark or offer any hostilities. I couldn't lock on it or find it by any other means than the binocs. After circling it twice I decided it was some English ambassadors yacht so I manually took control of the deck gun and after some 40+ shots at the waterline, the light ship secumbed to its wounds, lights went out, and she faded into the abyss of the deep, ... along with her escort.

[Pisces]

Exactly!! Well you was one of my teachers... :salute: ...My submerged "sprint" was perpendicular to the "fourth" i.e "predicted" bearing... almost at the same course... bearing rate changed for only one degree and triangulation bearing was kinda shallow-ish but I thought it was an effect of contacts speed...it turns out to be 9 knots, and my max submerged is 8... is this the mistake? Or did he just changed course in the meantime?I took your numbers of message 6 and ran it through this device:

http://www.subsim.com/radioroom/showthread.php?t=147719

If I understood it right, "6 - 7 - 9 degrees difference between them", means between the 1st and 2nd bearing was 6 degrees. And between the 1st and 3rd was about 13 degrees (6+7). The 4th (predicted) bearing would be 9 degrees further from the 3rd.

The last value we can't do much with, since it is the result of your drawing based on the previous two.

Let's see what 6 against 13 degrees says about AOB on that device. AOB at the 1st bearing would be: 50 degrees, which would be 63 at bearing 3. Well that is fine and all, but there are measurement uncertainties on those bearings. The hydro operator can't report hydrophone bearings with resolutions better than 1 degree. Copying them from the sound lines on the map allows you a bit better accuracy, but there would still be some inaccuracy. Let's compare pairs of numbers that are 0.5 degrees off:

5.5 aligned to 13.5: AOB1=26
6.5 aligned to 12.5: AOB1=105

Auch! AOB could be all over the place.

My conclusion based on this is that the 10 minutes are far too short to rely on the drawing. You need more time between the bearings to better show the bearing-rate acceleration. Then the possible AOBs wil converge to a more narrower range. Next time, double up to 20 minutes by reusing old bearings and compare the result.

Sorry. The sprint to the 2nd position wasn't the problem. The probably faulty AOB caused the range discrepancy in the first place.

[Shkval]

Well if I allowed myself the luxury of 20 minutes per bearing he would ran away... and chasing a contact on surface in narrow channel full of patrolling ASW trawlers and destroyers during zero visibility... well :timeout: a "little bit" too risky for my taste... bottom line waiting in confined space with the enemy sneaking around who you can't see until is too late... not a good choice... like a shark in a swimming pool... hydrophone plotting demands time, space, preferably slow contacts and of course decent visibility for check-up... ahhh the fog... thanks for your patience and time... still learning...