OK I just want to try and summarize things so that, I know I am on the right course here (pun intended) and to help make things really clear for anyone else who might being trying to figure it out for the first time or looking to make a quick TDC on their calculators. First, my reference diagram here is straight from the Silent Hunter Manual from the top of the thread.
From this you can see that what we need are:
- Target Speed V(t)
- Torpedo Speed V(s)
- Observed Angle on the Bow (b)
Using the above equations we can solve for the proper gyro angle (
a) with:
a = sin-1 ( (sin
* (V(t) / V(s) )
** sin-1 is the inverse sin function **
Remember that
a is the number of degrees ahead of the target's course you should aim. Donoby's nice TI-8x program does a lot of work dealing with converting your current heading and the targets heading to find the correct Observed Angle on the Bow (
b) all for you. In fact, most of his program deals with this. It can be tricky to keep the correct headings and bearings straight in your head so he cleverly layed down rules for his calculator so it will figure it out for him each time, all he has to do it give true headings (headings according to true North not relative bearings) and the target's bearing and it figures it out for him.