nataraj
11-23-13, 05:18 AM
The Stand
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Hunters use them to wait for deer.
Yesterday, on my third patrol (ever), I had a few hours (radio message at 1040, reached position 1730) while shadowing and overtaking a convoy. I used that time to figure out where exactly to lie in wait. I did some simple calculations and found out a few facts (see .PDF with graphic (http://helmut.saueregger.at/gameresources/SH3/HSTorpedo.pdf)):
fact 1: the solution to the gyroangle problem (what the TDC does) is independent of "Range" (but the effect of errors in the estimated target speed increases with range)
fact 2: as long as the target remains on course with constant speed (no zigzag, no circles), the optimum position, heading and moment of torpedo release can be pre-calculated very easily.
POSITION: in front of the target, slightly (600m-1000m) off target course, at periscope depth.
HEADING: target course +/- 90
WAIT: until the target comes a bit closer, take a peek: ID ship type (is it worth spending a torpedo?) and flag. Retract periscope. Enter the solution into TDC (manual mode), set up torpedoes. Faster is better, because the effect of errors increase with time.
LISTEN: when firing at a right angle, the correct moment of release depends ONLY on the relative speeds of target and torpedo. The target bearing at the moment of "fire" is
BRG = arctan( vTarget / vTorpedo )
This can be done easily on paper, not so easy with SH3 drawing tools. Here is the table:
<pre>
SPEED (kn) 4 5 6 7 8 10 12
-----------------------------------------------------------
SLOW 30 008 009 011 013 015 018 022
MEDIUM 40 006 007 009 010 011 014 017
SLOW 30 352 351 349 347 345 342 338
MEDIUM 40 354 353 351 350 349 346 343
-----------------------------------------------------------
(aft tube):
SLOW 30 188 189 191 193 195 198 202
MEDIUM 40 186 187 189 190 191 194 197
SLOW 30 172 171 169 167 165 162 158
MEDIUM 40 174 173 171 170 169 166 163
</pre>
"FIRE". When the target reaches the correct bearing, fire. I have not yet found out how to fire a torpedo "straight ahead", so I use F6, manual entry, set range to 800, bearing to the value from the table, AoB is 90-BRG (or BRG-270), should give a gyroangle of 0.
This also works completely submerged - I used the method first against the (only) destroyer escort of my convoy (no need to ID anything, radio had said "enemy convoy" ...)
Example: convoy course 250, I positioned myself with heading 160. Convoy speed 6 kn, I chose slow torpedo (30kn) -> target bearing 349.
Error Analysis:
I let my computer calculate the effects of errors in the estimates (speed, course, bearing etc.) and found out that at a range of 800 m, the distances between torpedo and target point (!) are mostly well within 50m, so even if the target course is a few degrees off, or the speed is <1kn off, the torpedo still hits the target ship.
at 6-8 kn target speed: error in course 25° -> 15m distance
at target speed 8,10,12kn (medium torp): +/-2kn -> 38m distance
target speed estimated 6kn, slow torp: +/- 2 kn -> distance 52m (MISS !!)
Timing: the target moves at 3-5 m/s, so 10 seconds error in firing gives an error of 30-50m ! This is the most crucial part, since near the moment of torpedo release the bearing changes quite fast.
---------
Sorry if this is common knowledge, I've not yet read all the guides (probably never will, better to find out some things by myself)
BTW, does anybody know exactly what bearing is reported by the sound guy: bearing to the center of the ship or to the propeller (should be propeller, but I should have had more misses or hits near the stern if that were the case). Hm :hmmm:
Helmut
----
edit Nov.24: Last night, I had ample opportunity to test the method outlined above. Two key findings:
(1) The hydrophone operator takes about 25 seconds to complete one sweep and update the position. That is too long for good aim. But counting seconds and firing at the right moment in between works perfectly.
(2) When I had only aft torpedoes left, I found out that - at least with the KDB installed - I could not get sound bearings in the required range (170-190). went to periscope depth and used the observation periscope in a second attempt ...
----------
Hunters use them to wait for deer.
Yesterday, on my third patrol (ever), I had a few hours (radio message at 1040, reached position 1730) while shadowing and overtaking a convoy. I used that time to figure out where exactly to lie in wait. I did some simple calculations and found out a few facts (see .PDF with graphic (http://helmut.saueregger.at/gameresources/SH3/HSTorpedo.pdf)):
fact 1: the solution to the gyroangle problem (what the TDC does) is independent of "Range" (but the effect of errors in the estimated target speed increases with range)
fact 2: as long as the target remains on course with constant speed (no zigzag, no circles), the optimum position, heading and moment of torpedo release can be pre-calculated very easily.
POSITION: in front of the target, slightly (600m-1000m) off target course, at periscope depth.
HEADING: target course +/- 90
WAIT: until the target comes a bit closer, take a peek: ID ship type (is it worth spending a torpedo?) and flag. Retract periscope. Enter the solution into TDC (manual mode), set up torpedoes. Faster is better, because the effect of errors increase with time.
LISTEN: when firing at a right angle, the correct moment of release depends ONLY on the relative speeds of target and torpedo. The target bearing at the moment of "fire" is
BRG = arctan( vTarget / vTorpedo )
This can be done easily on paper, not so easy with SH3 drawing tools. Here is the table:
<pre>
SPEED (kn) 4 5 6 7 8 10 12
-----------------------------------------------------------
SLOW 30 008 009 011 013 015 018 022
MEDIUM 40 006 007 009 010 011 014 017
SLOW 30 352 351 349 347 345 342 338
MEDIUM 40 354 353 351 350 349 346 343
-----------------------------------------------------------
(aft tube):
SLOW 30 188 189 191 193 195 198 202
MEDIUM 40 186 187 189 190 191 194 197
SLOW 30 172 171 169 167 165 162 158
MEDIUM 40 174 173 171 170 169 166 163
</pre>
"FIRE". When the target reaches the correct bearing, fire. I have not yet found out how to fire a torpedo "straight ahead", so I use F6, manual entry, set range to 800, bearing to the value from the table, AoB is 90-BRG (or BRG-270), should give a gyroangle of 0.
This also works completely submerged - I used the method first against the (only) destroyer escort of my convoy (no need to ID anything, radio had said "enemy convoy" ...)
Example: convoy course 250, I positioned myself with heading 160. Convoy speed 6 kn, I chose slow torpedo (30kn) -> target bearing 349.
Error Analysis:
I let my computer calculate the effects of errors in the estimates (speed, course, bearing etc.) and found out that at a range of 800 m, the distances between torpedo and target point (!) are mostly well within 50m, so even if the target course is a few degrees off, or the speed is <1kn off, the torpedo still hits the target ship.
at 6-8 kn target speed: error in course 25° -> 15m distance
at target speed 8,10,12kn (medium torp): +/-2kn -> 38m distance
target speed estimated 6kn, slow torp: +/- 2 kn -> distance 52m (MISS !!)
Timing: the target moves at 3-5 m/s, so 10 seconds error in firing gives an error of 30-50m ! This is the most crucial part, since near the moment of torpedo release the bearing changes quite fast.
---------
Sorry if this is common knowledge, I've not yet read all the guides (probably never will, better to find out some things by myself)
BTW, does anybody know exactly what bearing is reported by the sound guy: bearing to the center of the ship or to the propeller (should be propeller, but I should have had more misses or hits near the stern if that were the case). Hm :hmmm:
Helmut
----
edit Nov.24: Last night, I had ample opportunity to test the method outlined above. Two key findings:
(1) The hydrophone operator takes about 25 seconds to complete one sweep and update the position. That is too long for good aim. But counting seconds and firing at the right moment in between works perfectly.
(2) When I had only aft torpedoes left, I found out that - at least with the KDB installed - I could not get sound bearings in the required range (170-190). went to periscope depth and used the observation periscope in a second attempt ...