Advanced hydrophone lessons - calculating speed?

[Paul Riley]

I would like to begin a thread on advanced Hydrophone lessons ( not sure if they have been done before ) as I want to start getting used to gathering ship data without ever having to raise the scopes,ideally for late war scenarios or against warships.Initially I am wondering how to get quite reliable results on speed.I understand the theory in counting revolutions to get speed but don't know how to do it correctly,or even how to translate this data into speed results.
If there is a link to this info you could direct me to that,or just teach me from scratch,your choice :know:
I can say once I am close to mastering advanced hydrophone use to gather data I can start to enjoy the finer points of commanding a UBoat.
Maybe the next lesson could be 'determining ship course when submerged' ?

[Didd]

There was an excellent thread on this a short while ago, outlining a technique whereby you could determine course, speed and range (without counting rpms) and even shoot blind (target id may be an issue though).

There was a video if I remember rightly. I've got a pdf of the technique if you are interested.

Here's the link to the thread:
http://www.subsim.com/radioroom/showthread.php?t=154461&highlight=hydrophone

[Paul Riley]

Thanks for that Didd :up:
And yes,the pdf could be useful,thanks again.

[Didd]

Try this:
http://www.subsim.com/radioroom/showthread.php?t=160817

[Paul Riley]

I checked the first video,and it started well but quickly got VERY complex with lines and marks all over the place,a bit TOO complex for my taste.I am going to see if there is any official material on the web regarding how real UBoat captains plotted courses and gathered speeds while submerged,i'm not even certain if they did,I imagine submerged data gathering to have evolved and been more important as detection technology increased,leading to the birth of the nuclear submarine,which has the equipment to build an accurate picture of whats happening above totally submerged for months at a time.
Still,I wouldnt mind understanding how it can be done.
The pdf file may be a better option.

Thanks very much for your links by the way :yep:

[BillCar]

The video posted is the correct way to do it if it is going to be done (there's not really another way if you want speed, heading and exact range to target). This method was not commonly employed by U-boat commanders at all, but it does work. I don't tend to use it, simply because it does defy realism a bit, but on those rare occasions when I do, I find that it works quite well.

[Paul Riley]

The pdf is a lot easier to understand as it is broken down more and explained clearer,I just have a bit of difficulty with the final parts when triangulating the target.I think I will try and master this method just to get a rough idea of the course of enemy warships with powerful radar,whereby being on the surface would be too risky,against merchants or unescorted convoys I will stick to more traditional methods for getting course,speed,range ;)

Good read though.

[HetzerII]

Having read this with much interest...

what are the most accurate (historical) methods to do tdc manual? Some time ago i stumbled across paper-"disc" for tdc. Is there anything like that available to reproduce manual german tdc like it was used in wwII?

What are the most usefull tools if i want to plott contacts on paper to do the calculations?

[Pisces]

The tool to do the calculations:

http://www.subsim.com/radioroom/showthread.php?t=114351

The book on "how?":

http://www.subsim.com/radioroom/showthread.php?t=126824

But those are all modern recreations (by SH players) of what they(Hitman and KLH) think/investigated was used. Historically realistic as best as possible.

p.s. For hydrophone methods taking your time is the best solution to get accuracy. Bearings that change are a patience game. It's sloooooowwww! I follow the method of the movie/pdf-document but use my own 3-bearing AOB calculator disk (http://www.subsim.com/radioroom/showthread.php?t=147719) (which is not historically accurate btw) to get AOB/course. Start with short periods and double-up the time interval until AOB is acceptably accurate (use the 1st and 3rd bearing of short periods as '1 and 2nd bearing' of the longer periods) Then moving on a parallel course you can be confident you won't get dangerously close while taking the 4th bearing for his speed.

There has been an old mod for GWX 1.0x that allows screwbeat counting. But I doubt real uboats had knowledge of screwbeats vs. speed curves. Maybe some ships, or the operator could distinguish fast from slow, and/or accelerating/decellerating. They would still have to compare the beat counts with actual measured plots. This would only be usefull if you kept the target alive for another day to track. If you sink it it has become useless data.

ps2: the bearing where the target is supposed to have a 90 AOB is an excellent 'starting-line' to use for long-timeframe average-speed measurements. Move along for a couple of hours on roughly the same speed (guestimated). Or sprint ahead at moderate speed and wait somewhere until the sound is back at 90/270 degrees. The second bearing after a few hours is the 'finnish line' of sorts and you can develop an average speed between the lines.