JTS Wolfpack - Passive Sonar

[Lethal]

Hello Parmenio,

Apologies for my oversight!

Thanks for your assistance, I will let you know if I find anything.

Cheers,

L

No worries....

Where does one start when contemplating these numbers?

I think the period 1939-black May 1943 is of most interest.  And restricting the discussion to active/passive sonar and visual sensors of the combatants and the data presented in the JTS Naval Campaigns Manuals.

Background
By 1940 active sonar (ASDIC) could detect a submarine at about 2200yds (2000m) and was viewed as an attacking device.  Obviously, this is irrelevant when the U-boat is on the surface.  This was the method used to defeat underwater detection devices and surface attack was a feature of early U-Boat operations.

So passive sonar was very important for both sides early in the war.  A U-boat using GHG could detect a convoy up to 50nm, but could it determine a bearing?

The Game 
But, back to the game and the U-Boat in particular.  It appears to me the game is designed to have a U-Boat just out of visual range of the target, whether single ship or convoy.  It could be submerged or on the surface. 

Visibility and Sighting, p. 19 NC User Manual
Maximum visibility determined by scenario, can be variable.

Submarine Visibility and Detection, Standard Rules, p.39 NCUM
A submarine on the surface can only be detected at 1/2 the normal radar range of another ship.

Submerged Submarine at periscope depth, p. 40:
a.  periscope visibility range is half of ship visibility,
b.  the periscope can be detected at the Periscope Visibility Parameter Data value.

Enhanced Submarine Rules, p. 43
Night
At night, the maximum spotting distance to detect a submarine on the surface is halved.

Sea State
The maximum spotting distance to detect a submarine is reduced by the fraction – sea state/max sea state.
Example:  Calm water, surfaced submarine = nominal visibility.  Each increase in sea state (1-12) spotting distance is reduced by 8%.

Testing, Scenario #39_0916 Convoy OB-4, 1939

Misc Values:
Horizon: 30000yds
Periscope and Torpedo Visibility: 1000yds
Submarine Visibility: 0.8
Sea State?  From comments, presume 1

39-40.pdt Values
Side A: Allies  Side B: Axis

Sonar Guesstimates!
If the horizon is 30000yds (+-25nm) then it is reasonable to suggest that passive sonar is greater than that, say 40000yds (+-33nm).

Hope these ideas are useful for you.  Obviously, the numbers need playtesting to determine practicality.  The image below is from the scenario with the values suggested.  Why have two escorts not been detected? - stopped, slow speed?  need to check.  How is escort passive detection compromised by proximity of convoy?

Allied Max Sonar Speed - 20.  Presume kts?  (everything else in imperial)  If so, suggest too fast and is this graded in game, ie lower speed better detection?  Surface Ship Sonar Speed Modification, p.46 

http://www.users.on.net/~jennnie/JTS/ConvoyOB4.jpg