turn count vs. reality

[raduz]

hi,

I know I am a bit annoying but still, I wish to know whether the US torpedo parties used to use the turn count to get the speed of the target. Most likely, this is a question for history fans. The SH4, as it is now, doesnt allow this option at all because of bad RPM/max speed settings. Is this reflecting reality or not? Did they use it at least sometimes or never?

[mookiemookie]

From what I've read, they did. I just finished a book where it says Dick O'Kane bought a metronome for his sonarman on the Tang to use when keeping track of enemy screw counts. They would set it so it synched up perfectly with the screw turns heard, and could then easily tell if the tracked ship was speeding up or slowing down.

Without having the book here in front of me to reference and tell you for sure, I'd guess that they probably used the metronome to get speed calculations from screw turns as well.

[raduz]

then we should have the opportunity to use such option, too!:know: Lets discuss about it. I am able to modify the turn count (in certain limits) so that the hydrophone could be used. How would you like to have it?

[SteamWake]

This was discussed at length in SH3 forums. Look there for some good ideas. Theroy should still be the same.

Turn count could be used however there are a few variables as in the size of the screw and the number of blades (typically 3 or 4). Although a good sonar man could probably hear the difference and take a good guess.

"Definatly a destoryer sir.... listens intently.... running hard.... listens a few more seconds, Destoryer closing fast !".

[tater]

ONI 208-J has very few jap merchants with rpms @ speed, however. So the warship/merchant ID is OK, but speeds would be a total guess. It's counfounded by the fact the the japanese had many many types of merchants instead of a few standards built in large quantities. Once Liberty and Victory ships were rolling off the mass production lines, such screw counts would be far easier for a u-boat I think (fewer types to worry about.)

[joegrundman]

IN the 1952 US torpedo fire control manual (http://hnsa.org/doc/attack/) it says the following regarding turn counts in the section describing how to determine speed:

(3) TURN COUNTThe Approach Officer should have available for ready reference the most complete set of curves that he can obtain of different types and classes of enemy vessels. Their use will furnish a means of approximating the speed of an observed target. Due consideration must, of course, be given to wind and sea conditions and condition of loading as they increase or decrease the speed of any given R.P.M. Turn count is most valuable in determining a sudden change of target speed.

...

(b) Although five methods of determining speed have been given above, it still remains that under almost all circumstances Plot and TDC are the two primary methods which the submarine must employ to obtain target speed.





I'd say the implication here is that turn count was not considered a reliable and sufficient method for obtaining an accurate target speed, and is more used in a supplementary fashion for estimated speed assessments and noting changes in speed, which is what the game does anyway, right?

[Frederf]

If someone would make a flash like thingy as a trainer for turn count and target identification on the 'phones you can have my first born. Didn't someone do that for SH3?

[tater]

There was some testing done on this, and I think all the merchants sound the same, or all have a cutoff at some rpm value.

[raduz]

I'd say the implication here is that turn count was not considered a reliable and sufficient method for obtaining an accurate target speed, and is more used in a supplementary fashion for estimated speed assessments and noting changes in speed, which is what the game does anyway, right?
How am I supposed to note the change in speed if there are merchants doing 47 RPM @20 knots, and if they change the speed to say 13 knots, the RPM remains the same?

I agree, the turn count should not be used as a primary method of getting speed of the target. But according to what you have quoted (supplementary fashion etc), we should be able to use the turn count at least SOMETIMES, in certain cases. But we cannot do it at all, for a moment!

[micky1up]

i dont see why its such a hardship to get speed in the game afterall loads of ships where sunk so they must have got speed from sonewhere TPK or the plot speed is an easy thing to work out but the in game functionality is garbage

[greyrider]

well raduz,
your not annoying, i like your persistence!
the torpedo fire control manual states that speed curves for ship rpm counts were available,
and that the approach officer should strive to get and keep the most up to date speed curves available.
that says to me that it was important, you dont need speed curves to tell you if a ship is speeding up or slowing down, you
can hear that for yourself.
what we need to see are those speed curves, but we dont know where they are, if its classified information, or if they were destroyed
after the war for being useless.
some typical idiot politician opened his mouth back in the second war, gave the japanese some valuable information
about thier DC'S and how they were using them, and got ten U.S. submarines sunk in one month,
so finding things like speed curves might be impossible to find.

rad, if your can rework the engine and prop rpm's, use this propeller calculator,
http://www.csgnetwork.com/marinepropcalc.html
with this i was able
to get a propeller pitch for the small frieghter in sh3, it matched up with every turncount speed it had
accept at 3 knots, where it was one rpm above or below what it actually was, that was the only speed in the entire telegraph that
didnt match up, and that was the stock engine and propeller numbers.
if the engine and prop value's can be changed, i see no reason why the ships could not have an accurate prop pitch, we have everthing we need,
(engine rpm, prop rpm) we would have to play around with numbers for gear ratio's, and slippage, thats what i did with the small freighter,
but i didnt touch the rpm values because i didnt know how to.
can propeller rpm's be increased in the game?
if i was a submarine commander in ww2, EVERTHING would be important to me! every way and every idea to attack, i would explore, and master,
if it had merit, or was possible.
listen to this recording, its about sonar, listen to the sonar operator report on a sub 820 yards away, one of the items in his report
says the contact has a width of ten degree's, remember we talked about sound cone width? this is proof enough to me that they also used
sound width to determine a contacts range, it this case they pinged the sub for range, but width is noted.
http://www.hnsa.org/sound/soundinthesea/track30.mov

no one here can say for sure what they really used, i bet it was alot of everything, tactical situations vary, sometimes changing
in the middle of the game, fast.
this here is another recording of a u. s. submarine, using radar, to kill a kongo.
what fasncinates me about this recording is the desperation of the japanese radio operator,
and the way he keys his morse code equipment, sends chills up my spine.
if radar was used, which it was, the hydrophones could to.
http://www.hnsa.org/sound/sealion/intro.mov
http://www.hnsa.org/sound/sealion/sealionkongo1.mov
http://www.hnsa.org/sound/sealion/sealionkongo2.mov
http://www.hnsa.org/sound/sealion/sealionkongo3.mov
http://www.hnsa.org/sound/sealion/sealionkongo4.mov

[tater]

Very feew merchants had any screw counts at all though. I have the (classified at the time) ONI recognition manual. The few merchants that have anythign have 1, like Kinposan Maru: 82 rpm @12.5 knots. That's it, no other data.

The warships are similar, if they have anything at all, it's likely 1 count at 1 speed.

They just didn't have all that much data.

[raduz]

well, this is really interesting, grey. I always admired the sources and the archives you can find! the calculator seems to be a useful tool, however, it only could be used for the purposes of game if we were able to modify the RPMs so that it would correspond to the calculators range (up to 500), which is not possible IMHO.

the RPM can be changed easily, in the .sim files. but we will never be able to get the real RPM. I mean, we cannot do it so that 1 knot would be equal to a certain RPMs. we can only change the RPMs the way it was done in SH3 so that each class would have a specific RPM between 21 to 47 (merchants) or 42 to 94 (warships).

[SteamWake]

Very feew merchants had any screw counts at all though. I have the (classified at the time) ONI recognition manual. The few merchants that have anythign have 1, like Kinposan Maru: 82 rpm @12.5 knots. That's it, no other data.

The warships are similar, if they have anything at all, it's likely 1 count at 1 speed.

They just didn't have all that much data.

Well I guess if your a math wiz the rest of the speeds could be gotten from that baseline number. But that got me to thinking 82rpm=12.5 knots.... was that downwind? upwind? sea state ? A whole list of variables.

But from what Im hearing that in game the rpm does not change from say ahead full to flank making this whole thing pointless.

[tater]

Assuming speed and rpm were a linear relationship. And you are right, wind, current, sea state, etc would all have a bearing on this.

Bottom line is that only a few ships in the ONI manuals have even 2 data points for turns/speed. Also, the game rpms are grossly low. Ise says 318 at 23 knots. Nagato 330rpm at 26 knots. Most warships have nothing at all listed, actually.

[greyrider]

rad,

i see what you mean with the propcalc, it does'nt go high enough, i'll look around for another one, but i think i just might take a ride over to some of the propeller shops around here in marblehead, and salem, and see if i'm able to pick up some information from the owners.

there is also a gato class, or belayo,(forgot how to spell it) submarine about 40 miles away, along with BB uss massachusetts, a pt boat, and a german 2 man sub there.

i think i'm gonna ride there also, in a few days, see what info i can get from caretakers.

tater, your right, i saw one of them online once, and it had only one speed only, 11kts, i think it was a ijn cruiser, but that which we are talking about is a rec manual, these speed curves that the control manual speaks of seems to be something else.

[Frederf]

While it may not be historical to be able to tell what the captain had for breakfast and his speed down to the closest 0.1 knot by turn count, I wouldn't mind a trainer to get the feel for the difference between a 5 kt blub-blub-blub and a 9 kt bleb-bleb-bleb-bleb.

Also the hydrophone operator always knows if the ship is coming, going, or in between. How does he know this and is there any way I can figure it out myself?

[SteamWake]

While it may not be historical to be able to tell what the captain had for breakfast and his speed down to the closest 0.1 knot by turn count, I wouldn't mind a trainer to get the feel for the difference between a 5 kt blub-blub-blub and a 9 kt bleb-bleb-bleb-bleb.

Also the hydrophone operator always knows if the ship is coming, going, or in between. How does he know this and is there any way I can figure it out myself?

The comming / going was determined by the pitch of the sound altered by the doppler effect.

Just google doppler effect :up:

[Frederf]

I'm familliar with the doppler effect but could such pedestrian speed doppler effects (20 kts or so) be heard by the human ear? 20 kts compared to 770 kts speed of sound.

That's only a pitch difference of +/- 2.6% compared to something neither coming nor going away from you.

[raduz]

The SO is way too good when it comes to estimating closing-mowing away. He reports immediately any bearing change which is, IMO, not real. If you man the hydrophone, you can say the contact is closing or moving away, but you need at least two observations within a sufficient amount of time (lets say 10 minutes). The SO is able to estimate it in 10 seconds...

How does he know? IMO, the SO knows EVERYTHING about the contact: type, speed, position, vector etc. In every moment, he knows exactly where the contact is and what is he doing. However, he will only report a limited part of his knowledge, dependig on his skills and qualification. Remember, the SO = computer. The way he is simulated, is not based on real skills but rather on limitation of information you get from him.

[greyrider]

these two links here show what to look for when a contact is moving toward the hydrophone, and away from the hydrophone.

there is at least 3 parts of a sound signal: the propellers, the engine sound, and auxilary sounds,(pumps and other equipment).

in sh4, we have two, prop and engine.

in sh4, the SO, can tell when a contact is closing because the sound cone grows in width, whereas in moving away, the sound cone width diminishes.

in closing there is a mass of noise, and when moving away, the noise diminishes.

altho sh3 and 4 have been outstanding games, i think we still have a long way to go with modelling sound properly.

sh3 and 4 sound nothing like the records of the sonobouy, as a contact gets closer, sometimes the engine, or in this case, the electric motors will drown out the propeller beats, this doesnt happen in sh. the propeller sounds are always heard above the engine noises. this could give you a range determination if you know at what range the engine noises overcome the propeller beats.

thers so much to learn in this area, and altho these sonobouy records sound nothing like sh, what they do is show what to look for in a sound signal from contacts.


http://www.hnsa.org/sound/sonobouy/sonobouy02.mov

http://www.hnsa.org/sound/sonobouy/sonobouy13.mov

[greyrider]

rad, here is a propeller calculator that will work, i put in 100,000 rpm, with a 2:1 gear ratio, 10% slip, and boat speed of 10 MPH,
and the propeller pitch was .2 inches.
that was just a test throwing numbers around to see if this calculator could handle large values in the engine speed rpm entry.
it can handle it, so this is the calculator to use.
if you going to try to mod the rpm, give slipppage percent no more than 20 percent. plug in different values for GR.
if you think it can work, i'll help you, its going to be alot of work.
http://continuouswave.com/cgi-bin/propcalc.pl

[raduz]

thanks grey, I will check it ASAP