Lol .. after even harder googling, I tried search here, at subsim .. so .. something is here:
http://www.subsim.com/radioroom/show...ht=demon+blade
and here:
http://www.fuzzytech.com/e/e_a_kumm.html
All around .. you mostly don't get blade count, since shaft, at least on subs, are build to give no sound. All you get is blade noise, and you are mostly not sure if you get blade frequence or double blade frequency or even triple blade frequency (2nd and 3rd harmonic). So it surely needs good operator to get some data from it.
You only can get blade count if there is distinct shaft line (which usually is not the case). Then you'll see first line of the shaft, next line will be it's 2nd harmonic (double frequency), then 3rd and so on .. they'll be weaker and weaker. Then there will be blades line. 5 bladed propeller has blade frequency 5 times the shaft frequency. That means quite strong blades line will be at the same position as 5th shaft line. Blades frequency will also have some visible harmonics.
So you'll get something like this:
O o , . O . . . . o . . . . , . . .
O o , . O . . . . o . . . . , . . .
O o , . O . . . . o . . . . , . . .
You see strong line is the 1st line, the shaft, and then each 5th line. This show that there are 5 blades. First 5th line is blades frequency, other are blades harmonics.
But it seems with subs you'll get more often something like this:
. , .
. , .
. , .
. , .
Now you know nothing without classification and good intel. That can give you lot's of usefull information. Blade count in the first place. Tentency to show 2nd blade harmonics more loud then first blade harmonic, and many other things.
Then you could say .. yeah .. the strong line is twice blade frequency. There is something weak at the half frequency. That would be 1st blades harmonics. Blades count by classifications is 7. So TPS is strongest line divided by 14 (!). That by TPK gives .. lets say, 7-8 knots. Or .. it is some different sub at quite different speed .. :-D