Relating back to the original question; I have run into quite a few ships such as the smaller coastal merchants, and even coastal gun boats that will not be detected by the hydrophones. I even have a list compiled ( not on me at the moment ).

When I encountered a visual contact without a corresponding sound emission I wrote down the conact and went in the mission builder to recreate the situation. In most cases speed was the predominant factor. The ships were not detectable in the phones at speeds less then 6 knots or so. I even tried changing weather conditions which had little effect. I think I a had about a 6 ships listed that I had done testing on.

Even stranger was that in some cases my crew would detect the target and would track it, but when I took the phones I could hear nothing.

I have not fould one IJN combat ship with this issue.

I am running 1.5 with RFB and RSRDC.

Interesting, I too have had the same issue. Although I caught it by accident, as I have been using my hydrophones myself a lot, and have heard contacts, not sure of the range or the type, but sounded loud enough to be detectable to even the most untrained of sonarmen.

Will post back if I can find anymore info.

If you can post the list here it could be possible that there is no sound attached to those ships. There aren't separate entries for each ship.

Do you have any sound effects mods installed or did you stick with the default RFB sounds??

Yeap. I've occasionally come across this behavior too.

RFB swaps out nearly ALL of the sound files for the hydrophones.

I personally have not had any trouble with them and often find distant, un classifiable contacts that my sonar man doesent. As I said before with RFB you can even pick up 'stationary' contacts.

All I can think of is 1.) your not deep enough and still in the surface boundry 2.) Something is wrong with your hydrophone gear or 3.) Your install of RFB is screwed up.

With RFB you cannot pick up contacts while surfaced, none, nada, nothing. Usually going to Periscope depth is enough, but just to make sure I typically go to about 80 feet.

I had some time to kill today so I played around with the mission editor. I started from the bottom of the list of IJN merchants starting with the small old split freighter and worked my way up.

Here is how the scenario was set up. I place the merchant heading north toward Kiska. Speed was set at 10, then 8, then 6, 5, then 4. My sub was placed about 4000 yards off the starboard bow of the incoming merchant at PD and then various depths to test the phones.

So for the first test the merchant's speed was set to 10 knots. On the phones she came in loud and clear no matter what depth ( except surface ). Same result for speeds of 8 and 6 knots but when I dropped below 6 knots I could not detect the target even though my crew tracked the merchant just fine. Any speed below 6 knots had the same result.

I repeated this test for the first 5 merchants in the IJN list and had identical results. Once a merchant dropped below 6 knots it was not detectable on the phones even though my crew could track the target and I imagine if my realism was cranked down you could see the sonar bearing line as well.

These results were confirmed regardless of depth and speed of own ship but of course you have to be submerged and atleast PD to use phones.

I have no doubt that even if the merchant was dead in the water my crew would find her even though you would not be able to track her on the phones yourself. Sounds like I need to test that one.

I have not tested the same hull from multiple nations but I cant image they would be any different. Is this new information? Probably not but it does seem to relate to many questions above problems with the hydrophones.

I seem to vaguely remember something in the 1.4 or 1.5 patch read me files about this change but I havent gone back and read it again.

I wonder if anyone else has had similiar results?

One more note, my install is very clean and recent, but I am not ruling out that my install could be corrupted I just have no reason to suspect so.

I know this is an old thread, but I too am experiencing this problem.
I'm able to replicate the 6 knot threshold as eplained above. Just wondering if anyone might have any more information on how to remedy this?

thanks!
Evro

I remember CapnScurvy mentioning this unusual phenomenon and this was his answer.