Thread: Hydrophone help
View Single Post
Old 07-22-2020, 05:49 PM   #5
Silent Hunter
Join Date: Dec 2004
Location: AN9771
Posts: 4,779
Downloads: 278
Uploads: 0


Originally Posted by CommissarStarfish View Post
I've had the game for four days now and I've figured out that I have the most fun as sonar/radio man. I know how to find and zero in on targets but I don't know:
How to find distance to the target
How to find out which way the target is moving
How to calculate target speed
How to calculate target size

If anyone could help me out with one or multiple of these things that would be great.
The hydrophone is not the right tool to figure those out. The target is an entire convoy of multiple ships. You don't know exactly which ship the sound you are listening to belongs to. As such, from a slightly different angle you could pick up a different ship as the loudest sound source the next time throwing off your tracking effort. Also, some ships may have a louder or weaker sound level. So you can not determine if the ship is loud but further away, or quieter and closer. This distance to the target based on volume thing is extremely unreliable to put a number on it.

You don't even need to know the distance. It doesn't help much. The quickest and simplest way to get eyes on it is going towards the sound. Simply follow the sound. It is just beyond visual range in the game. And the convoy is generally large enough so you can't miss it. If you really want to account for their movement you just wait a little and see how the direction to them changes. Does it go left, or does it go right? That takes halve of the circle of possibilities away. You can't tell much more than that in the short term. If you have patience enough (I'm talking sitting still and listening for hours) you might be able to tell if the bearing drift slows down or speeds up. This tells you if it is receding or closing. As a train passing a crossroad you are standing next to zips by your face, while a distant train close to the horizon appears to move like a snail.

Knowing very roughly where it is going you might consider to get ahead of it a little by steering to a course that comes in front of it. How much? Not really possible to tell. But with some simple trigonometry, an assumption on their worst case speed going perpendicular to the line of sound and your best speed of 18 knots on the surface, you can estimate the lead required to get ahead. Likely they move no faster than 9 knots, worst case are pointed perpendicular to the sound bearing, and you move at 18 knots to intercept. This suggests to lead by 26 degrees, give or take. It doesn't require more precision than that to gain advantageous position. Just patience and a watchfull eye of the bridge lookouts. Make sure you drill your (fellow) crew to be watching. Or the escorts will see you first.

Target size. I already mentioned, it is a group of ships. Each has their own size. As a whole it could be kilometers wide. All the sound merges into one big cacophony, dozens of degrees wide. You will at most be able to narrow down a few peak sound sources (with minimal gain to let it just distort) where there can be dozens in the convoy. The only way to tell how large they are is by looking at it. So postpone that question and let the person at the bridge, uzo or periscopes answer that.

Target speed. Good thing, they all move at the same speed, and course. That is, if they are still unaware of you. They may (and 'will' with harder difficulty settings) change course from time to time. Which is another reason why it is of little use to spend time on getting accurate values of speed and course at the early stage. When they do change course and speed you will see that better when you actually look at them.

And when I write 'they' or 'their', I mean the merchants, tankers and liners. They are the cows or sheep in the herd. Focus on them for telling you where they go. Escorts make numerous sidesteps in their attempts to find you. They throw too many curve-balls by sprinting all over the place.

So how do you get their speed and course?

It is far easier to figure it out with visual sightings. And trying to match your own movement to theirs. If the bearing to them, like a specific mast, does not change for a long time then you are either closing to or moving away directly from it. If you can observe that neither of the two is happening (Does it grow bigger or becomes smaller in the periscopes?) then your course and speed is the same as theirs. Ok, but how do you do that? Observe how their bow is pointing in the view away from the line of sight. This is the Angle on Bow setting on the TDC. How much must their captain turn his head to look at you. Are you looking at it's back? Is it exactly side-on? Or just in front of side-on? Or more to the front. If you are lucky there are masts visible that are side-by-side eachother. When they line up then you can be sure the AOB is 90 degrees. And their course is perpendicular to the (true) bearing you are looking at. But most likely it is not a nice round number and you have to guesstimate. That takes effort and practice, but you will improve in that. (Just drive around the ships in the training scenario and check your assumptions to the shown solution on the map) If you set the TDC to the viewing device with the selector switch then you can figure out their course too. As then the AOB is 180 when you are pointing at the heading that is their course. Set course to that and follow them moving parallel. Then all it takes is to slow down or speed up to keep that bearing to a fixed point steady over some time (minutes long).The Engine order Telegraph can be used to slow down or speed up in increments of 10 RPM.

Presto, you have the first estimate of target speed and course the same as your own ship.

Can you get a more accurate number for their course? Yes, move directly behind them, or a place that is more tactically usefull, right in front of them. Being in front it is very easy to see when the AOB is exactly 0. Strafe gently across their path with a small course deviation. Once it looks exactly symmetrically then set the AOB dial to 0 if it wasn't already. Note the true bearing at the bottom of the attack periscope and figure out the opposite direction. That is their course. And you can plot an attack position from that in the future. Also note that as you are right in front of them you know they are on a line from where you are now. This line can be used later to get a fix on their position from another place. With multiple fixes like that from different places that you have been/will be, and the time in between you can confirm your estimates of their speed. At the least you can move away from that course line and set up perpendicular to prepare for an attack.

Is there really no way to do this with hydrophone?

I've been trying to put this off for as long as I can. Because, as said, the hydrophone is not the right tool to use for that. It is too crude. Bearings are not precise enough. The techniques to do it were not invented/used until after WW2, with better sonar equipment. But there are ways, if you are up for arduous time-wasting efforts. With (4) bearings alone. The manual shows one, but geometrically the explanation leaves a bit wanting. Properly using mathematical geometrical methods takes out the trial and error of placing lines at the right spot. If you really want to know: take a look at this document:,%20Neuro.pdf

I have a few similar documents in that webfolder describing the techniques in different ways. Just remove the filename from that link to have a peek in the folder. It is the theoretical way to do it. Perhaps more suited later when you can set your own mission parameters from a longer distance. You can even get their position, speed and course while keeping on the move. But longer time intervals will provide better results, and as such it may be a waste of time. Getting to it directly and visual will also get the job done.

Last edited by Pisces; 07-22-2020 at 06:11 PM.
Pisces is offline   Reply With Quote