[TorpX]

Originally Posted by Dorjun Driver

TorpX, I'm still getting 17.4 degrees. Perhaps I transcribed my "working" Casio/Excel formula improperly. I'll check into it.

I think the difference is because you designate your angles differently. When someone says "track angle", I use the track angle as per the USN. I keep to using it, and it has made my SH life much simpler. When you first posted your formula, it gave me the right answer, but I had to see how you marked the angle, first.

Comparing the deflection angles generated from your equation with deflection angles picked off Plate XVIII from SLM-1 yields small discrepancies, which increase somewhat at higher target speeds. I had always assumed that Plates XVII and XVIII in SLM-1 were accurate. The text implies that they include various correction factors and that they are substantially the results generated by a WW2-vintage TDC. The text does not indicate directly how the curves were generated, or what factors were included in the calculations. I had also assumed that the curves were somewhat more accurate than a first-order trigonometric analysis, such as the one in your OP. Apparently, my assumptions were incorrect. I would appreciate if you could tell me why the SLM-1 data are not to be trusted. I do agree that a first-order analysis is perfectly adequate for our purposes.

I took another look at plates XVII and XVIII. I then broke out my trusty TI-85 and set it to graphing my formula for lead angle using their parameters. The results, as near as I could see, looked close to what the plates showed, but not exactly. This puzzled me at first, but on closer thought, I think I know why.

We are solving a simplified problem, where no allowance is made for the distance between the torpedo tube and the periscope, and none for any launch delay, torpedo acceleration and such. Any delay or sluggishness of the torps would have the effect of increasing the deflection angle and could account for the discrepancy.

"10 degrees. 15 if he's going fast."

Speaking of Q & D, in WAR IN THE BOATS, the author mentions using a rule of thumb, "speed plus three". It certainly has the advantage of being simple, but I haven't tried it.