You're problem may not be your calculations. Go to the targeting fix mod and read what Capn Scurvy found. he also provided a fix for it.
http://www.subsim.com/radioroom/showthread.php?t=126016
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"There are only two types of ships- submarines...... and targets" Unknown
"you wouldn't catch me on a ship that deliberately sinks itself"- comment to me from a surface sailor. 
System:
AMD 6300 3.5 GHz | 32GB DDR3 | SATA 300 320GB HD, SATA III 1TB HD, SATA III 1.TB HD | ASUS Sonar DS sound card
NVIDIA 1660 Super OC | Windows 10
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