Hydrophone Use
 

Last week, a gamer asked in my Optical Targeting Correction thread:

I gave him an answer referring to the stock game as the problem. Either the sound files are missing or some other issue that doesn't relate to OTC. While this is true in some cases, I've done some in-depth tests to see just what's happening with the passive hydrophones and your ability to hear some target engine sounds and not others. It's not related to OTC, nor is the issue initially related to any mod. Although, any mod adding single or patrol missions (campaign missions) to the game could be causing the problem. I've spent well over 20 hours testing the hydrophone, its capabilities, its short comings, and have found the following.

The targets actual speed compared to its maximum rated speed is what allows the target "hyd" sound file to be heard. Simply put, if the target's speed is less than half the rated maximum speed for the ship......you won't hear a thing through the passive hydrophone. Turning the sonar dial all you want, you'll not hear the target. Even though your Sonarman called out the detection and displayed the results on the message text board. Having the target traveling at least half the maximum speed (or greater) allows for the target to be heard through the passive hydrophone use.

Unfortunately there isn't anything that can be done to change this within the parameters of the Sensors.sim file.

http://i175.photobucket.com/albums/w...ps4fd21dc2.jpg

Above is the RFB 2.0 Sensor.sim file found in the "Data/Library/USSubParts/" folders. There are 4 entries for the different hydrophones types RFB uses. The hydrophone that's highlighted is the "ball" type found on the S Class type boats. The others are similar, except for the MaxSensorHeight parameter and the MaxRange. The RPMDetLevel my cursur is pointing to, I thought, has something to do with detection. The short version.....this parameter doesn't change a blessed thing! I had it with negative numbers; positive numbers from fractions to 100.....and nothing changes. If a target ship is traveling below 50% of its maximum rated speed found in the target ships .sim file.....you'll not hear it through the hydrophones.

http://i175.photobucket.com/albums/w...ps6c409d99.jpg

Believe me, I tried several different things. Nothing changed the outcome. Except for raising the cruising speed of the target ship, or decreasing the specific ships max_speed parameter in the above file.....your hydrophone pickup of sounds will be nonexistent.

Just thought you folks that write missions should know.

Very interesting and helpful to understand. Thanks for your time and dedicated research Capn. :salute:

I made an interesting observation right now. I detected a ship with the hydrophone which was definitely travelling very slow, less than 5 knots. As it got closer, the sound all of a sudden dissappeared. When it came in sight I checked the speed and it was 4 knots. I waited until it was out of sight and guess what, the sound came back!!!

Uh Oh
 

All the more reason to do an all around periscope search before surfacing.

Trust that hydro man, who has the training that you didn't Captain.

Also...in a game I had hydro tell me there were screws out there but my scope showed nothing at all. I don't remember if it was in SH4 or SH5, but that contact turned out to be an enemy submarine.

Fun, eh?

So true :yep:

Once, after escaping an escort search, i thought all was finally ok, and thought i was far enough for my safety...no hydro sounds around nor my hydro guy was detecting anything...so i raised up to periscope depth, and what a bad surprise! :doh:
Was surrounded by 3 destroyers quite close! Few seconds later, all was to do again...as they spot me in this damn calm sea.
Re-depthcharged :nope:

That is strange.

I'll need to test further if the closer the distance to target makes this kind of disappearing sound. I've let my target ships come close, even let a couple pass by the sub, but hadn't run into the sound being heard one minute.....the next disappearing.......then coming back again as it goes away.

As far as a ship going slowly, like 5 knots, the propeller sound will still be heard as long as the "max_speed=" figure of the Propulsion/Propellers parameter is 10 knots or less. If the ship has a max_speed=12 or greater, you'll not hear it at all.

One way to get the disappearing sound you described is the possibility the ship hit a waypoint that slowed it down to 4 knots (less than half of 10), then it sped up again. I'll check to see if this could happen with my test ships.

The trouble I see of some mods trying to change the "max_speed=" parameter to suit realistic maximum speed figures is that increasing this figure will cause a game mission target ship not to be heard with the hydrophones with manual use. The game patrol/campaign missions are set to specific ship cruising speeds. If we mod an increase in maximum target speed, we mod the ability to manually use the hydrophones right out of the game.

Thanks, Capt. This explains a lot.
I have a question: does the speed and/or direction if one's sub have any effect?

Not for using the manual hydrophones.

I took the sub up to flank speed and did constant circles. You either heard the specific targets or didn't, due to the target cruising speed set below 50% of the ships max_speed, or not. Those targets traveling at half maximum speed or greater could be heard at any sub speed, and any relative bearing.

There is one "normal" area that makes it hard to hear a target when running the subs engines (to the rear of the boat), but the target is only drowned out for a small degree of bearing at the 180 degree area. If you listen closely, you'll be able to make out the rhythmic drumming of the target engines just a few degrees off the 180 degree mark.

The manual hydrophones can be effected by the subs height in the water depending on the type of hydrophone you have (usually set by the year date, or the specific sub type). The S Class "Ball" mount needs to be submerged in order to work. It sits on the deck like a large gazing ball. So does the early "rotation head" type found on the Porpoise and other early war subs. Stock and most mods have different settings for this feature found in the below file:

http://i175.photobucket.com/albums/w...ps4fd21dc2.jpg

The "MaxSensorHeight=" changes the required height the sub needs to be in order to pick up hydrophone sounds for both the manual and AI Sonarman. In the above RFB file the maximum height is just one meter below the waterline for the S Class ball Hydrophone. The later Hydrophones/Sonar heads are mounted on the bottom of the hull, so this figure is set to zero in their specific parameters.

The AI subs Sonarman is certainly effected by the subs speed and direction of the sound. This is done through the Data/Cfg/Sensors.cfg file:

http://i175.photobucket.com/albums/w...ps80b07d66.jpg

Changing these parameters will have the Sonarman either deaf as a post, or the only guy who can hear a pin drop!

I was able to reproduce the situation where I could hear a ship with the hydrophone as long as it was out of sight. Way before it could be seen, the sound disappeared. BTW, I am using SH4 1.5 with OM+OMEGU.

Thanks Capt.
The professional expertise of posters on this forum amazes me.
:know:

Without knowing more details about the particular ship you ran into I can't say for certain what happened in your particular situation.

I can look into mission files from Lurker and see what's what. So I did. One of two single missions that he adds with his OMEGU_300 mod is called "RUM 430430 U515". It has the U-Boat 515 attacking an allied convoy on April 30, 1943. Taking a look at the convoy makeup and speed, I see a potential problem with some of the ships. Several are of the KSS or Kasagisan type (Small Old Split Superstructure). OM-OMEGU has the KSS class freighter "NKSs.sim" file listing the "Max_speed=11" knots. The following mission file has these ships cruising at 5 knots:


http://i175.photobucket.com/albums/w...pse14bbf75.jpg

It's my opinion these ships will not be heard using the hydrophone manually. There are other ships in this convoy that can be heard because their "Max_speed=" parameter is set to only 10 knots.

As I said, I don't know all the particulars with your situation. I've only looked at this one mission, but it's the first mission I looked into.....However, this oversight in having ships travel at less than 50% of their maximum speed will cause not hearing the ship with manual hydrophone use.

Capn, I am not trying to argue with you. I noticed the same thing you reported already. I am just adding my observation to yours.

Believe me, I didn't think you were arguing with me at all! :up:

You pointed out an example that needed to be looked into, and I did a little bit of investigating into OM_OMEGU, checking into its mission makeup. Turns out there are some real reasons why the hydrophone deafness occurs.

When folks report issues that are similar, it only gives a bit of credence to the issue at hand. My digging into the actual files only proved there are some reasons why things occur as they do. It may not have answered why a sound was heard at a far distance, yet unheard as the target came closer, but it does point to issues that are similar.

I mentioned in another post, that a ship could change its speed after hitting a waypoint designed into its mission/patrol makeup. Mido, this could account to what you so aptly described. Also, another possibility is the ship slowed down as it made a direction change at a waypoint. I don't know for sure, but it may be possible for a ship that's cruising at just its 50% of maximum, MAY slow down a knot when it makes a turn. If it does, the hydrophone sound may go silent while the ship travels at this reduced speed. I don't know for sure about this......it's just a thought.

Thanks Mido for your input!! :salute: