[raduz]

Originally Posted by Sailor Steve

I'll have to recheck my books, but the RPMs listed on that chart have nothing to do with real life.

The fact is real submariners tried firing without visual contact, and failed every time.

why do you think so? let me quote greyriders discussion on this topic :

Originally Posted by Redwine

Mmhh... :hmm: I think so that was not the method in that age.

... in WW2 age, the periscope was used to determine range.

I am not sure they can determine propeller turns/min in that age, plus they need the data about how many knots per turns is corresponding to that ship. I think so they had not that data in that age.

Originally Posted by greyrider

i hate to say this, but redwine has given you wrong information, this method was used by american submarines in ww II.
propeller pitch was known then as it is now. TMA is a more modern way now. but not then.
below is taken from fleet submarine.com, which is all about wwII
fleet submarines of the american fleet.

http://www.maritime.org/fleetsub/

How to take a turn count
1. Train the hydrophone directly on the bearing where the prop beats are loudest.

2. Turn the prop-count detector ON. It may bring out the beats more clearly. (If it does not, turn it OFF.)

3. Notice whether the beats are accented or unaccented. Accented beats go CHUG, chug, chug (three-bladed propeller)-or CHUG, chug, chug, chug (four-bladed propeller). Unaccented beats go chug, chug, chug, chug, chug.

4. Get in rhythm with the beats by pumping your arm up and down. If there is an accented beat, let your hand come down with every accented CHUG -or if the beats are all the same, on every chug.

5. Count the number of times you pump your hand down in 15 seconds.

6. Multiply this count by 4 to get the number of rpm (revolutions per minute). Report the rpm immediately. For example, if your 15-second count is 24, the rpm will be 96, and you will report: "JP, turn count is ze-ro nines six. Good count." If the beats are so rapid that you are not sure of the accuracy of your count, report: "Poor count."

7. After you have reported, make sure that the prop-count detector switch is OFF.

as you can see, it was used in ww II.

http://u-boot.realsimulation.com/