Calculating position, real course and speed only by hydrophones!

[Mittelwaechter]

Interested in plotting a contact-course, position and speed only using hydrophones? Read on!


U 42 is hunting for single merchants in the Western Approaches. It's 2300 hours, the sea is calm. The sky is cloudy and two hours ago a light fog came up.
The Kaleun has ordered all engines stop at periscope-depth, Heinz is listening at the hydrophone for contacts.

"Contact! Freighter, inbound. Bearing 60°."

Konrad - our WO - activates the stopwatch and orders Heinz to report the bearings exactly all 8 minutes. Konrad notes the contact on the map. He draws a line of 20 km length from our position - bearing 60° to our bow.
Additionally he grabs a green pencil and draws a perfect circle (he's a genius!) on a free area of the map and marks the center with M. He draws the horizontal diameter and marks the ends with P1 and P2. The contact is reported on the starboard side, therefore he marks the right point P1. The line P1-M shall represent the distance the contact will travel in 8 minutes, the line M-P2 shall represent the distance for the following 8 minutes. Logically the length of both lines is equal as long as we assume the contact is moving with constant speed on a straight course.

8 minutes have passed, Heinz reports: "Contact now at 50°."

Again Konrad starts the stopwatch and notes the bearing on the map - a line of 20 km length - 50° to our bow. He notes the angle of the bearinglines - 10° - and names it A1.
He calculates: (180° - 2A1) : 2 = 80°. He grabs a blue pencil and the protractor to construct an isosceles triangle under the P1-M baseline - both angles read 80° - the sides meet in Point C1. The angle at C1 reads 20° (2A1).
Konrad - a golden colour pencil in his hand - draws a circle using C1 as center and the line C1-M as radius.

"Contact at 34°."

Our WO orders "Full speed, Heading 270" and reactivates the stopwatch. He notes the new bearingline carefully on the map. The new angle reads 16° - marked as A2.
To complete his auxiliary drawing he calculates again: (180° - 2A2) : 2 = 74°.
Using the blue pencil he constructs the second triangle similar to the first procedure, but now under the M-P2 baseline. Both baseangles read 74° - the sides meet under an angle of 32° (2A2) - the point is marked as C2 and used as center for a circleline - golden coloured - which meets M.

The two golden circles show two points of intersection - one is already marked M - Konrad names the other one U using the black pencil.
"U" represents the position of an U-Boot that locates a moving contact under the bearingangles A1 (10°) and A2 (16°).

Konrad draws the angle U-P1-P2 in red - it reads exact 33°.

He transfers this angle to the first bearingline representing the first contactreport at 60°. The new arm reads the quite exact courseDIRECTION of the freighter.
Fat chance the freighter doesn't move along this line but on a parallel courseline.

The intersectionpoints of the transfered courseline with the three bearinglines cut the courseline into two equal parts. They represent the distance our freighter moved in 8 minutes.
Konrad extends the courseline by 50% ("s") to mark the theoretical fourth bearing Heinz would have reported after 8 minutes without changing the position of the U-Boot.
He draws the bearingline to meet the new end of the courseline.

Seven minutes have passed since Heinz's last bearingreport. Our WO orders all engines stop to enable Heinz a proper report after 8 minutes.

"Contact! Freighter at ..."

Konrad notes the new bearing on the map. The line meets the theoretical fourth bearing in the freighters current position.

All necessary information to start an optimal attack is collected: position, course and speed (well you have to do some calculations on your own!) of the contact.

"Kessler! Wake up our Kaleun! We've got a job to do."


To confuse you even more - this shows Konrads auxiliary drawing. The colours are used in the correct chonological order. Well therefore it's in german.


And here Konrads NavMap notes.


Good Hunting, Gentlemen.

[GreyOctober]

Wow Mittelwaechter very nice narrative and very informative. But i somehow find your method too complicated. What i usually do is once i locate a contact by hydro i allow myself a minute or so to figure out the general direction of the contact my moving the hydro angle 2-3 deg left and right of the target. Once i figure this out, i make a mental note on the amplitude of the sound and start the stopwatch. I then move the hydro angle ahead of the target by several degrees and wait for the contact to intersect it. Once it does so, i stop the stopwatch, listen for the sound amplitude and note the bearing change. This will give me a rough estimate of the contacts speed and bearing and i can move to intercept.

Cheers!
Grey

[raduz]

you guys can find all this and even much more here:

http://www.subsim.com/radioroom/show...ophone+hunting

[Mittelwaechter]

Complicated but capable to sink contacts without even viewing them.
You may position your U-Boot at the right place and do some manual TDC settings to hit the contact in heavy fog or with periscopes destroyed.

You get correct speed, AOB and distance whenever you want.

[P_Funk]

I felt good when I figured out AoB way back.

This makes me want to cry.

[Sailor Steve]

Originally Posted by Mittelwaechter

Complicated but capable to sink contacts without even viewing them.
You may position your U-Boot at the right place and do some manual TDC settings to hit the contact in heavy fog or with periscopes destroyed.

You get correct speed, AOB and distance whenever you want.

Pretty good, since no one ever did that successfully in real life. Once again the game cheats.

[Mittelwaechter]

Well "the game" allways cheats as long as you know your exact own position on the NavMap.

Have fun with it - or simply don't do it.

[Canovaro]

Looks interesting, will study it closer later.

[Mooncatt]

does look really good, however if i tried it it would probably look like a dot-to-dot and resemble mickey mouse and miss completly

[Canovaro]

Originally Posted by Mooncatt

does look really good, however if i tried it it would probably look like a dot-to-dot and resemble mickey mouse and miss completly

:rotfl:

[Vandecker]

Thanks mate, just figured out how this method works, It's taken 3 hours thinking about it and trying to copy out the map as you draw it felt like I was for a long time. But I did it and am now off to try it for real. Thank for this I've been having real problems plotting courses by visuals, now all I need to figure out is a rough range and I can plot an intercept.

Again thanks

edit: hold on a moment! what the hell do you move the U-boat for?? it dosen't apear to be neccesarry to calculate the course??

edit edit: OH NICE! The theorietical fourth bearing from your original position intercepts the actual contact bearing at your new position giving you the course and distance of the merchant from your U-boat rather than a parallel one. Brilliant.



Edit your narrative slightly, give step by step diagrams, and get the moderators to sticky this thread, this is fantastic!

[jmr]

Originally Posted by Vandecker

Edit your narrative slightly, give step by step diagrams, and get the moderators to sticky this thread, this is fantastic!

This would help a lot at least for me. No roleplaying, just a straight up "how to" along with having having Konrad's auxilary drawing in English.

[Dantenoc]

Originally Posted by jmr

This would help a lot at least for me. No roleplaying, just a straight up "how to" along with having having Konrad's auxilary drawing in English.

Yes please

[High Voltage]

This Kaleun has to go lie down as his head has been pounding ever since he read the above post...

[Vandecker]

It works!! only problem with this method is if the bearings are too small it requires a full page to work it out... or a very very small initial circle