SUBSIM Radio Room Forums - View Single Post - "Snap Shot" -- to answer your question Johnfb

Alfred Keitzer · 01-31-12, 01:01 PM

Not quite -- you can do it that way, but not required. You don't have to leave the periscope at 0 -- that was just for the demo so you could see the lead (off the nose) computed for different target speeds; and to show you how range has little to no effect on lead angle provided you are shooting within 30-35 degrees of your bow (or stern).

Momentarily turning the TDC off, you have control over the TDC settings. Setting the target speed to zero causes the TDC to compute zero lead angle -- because it thinks the target is not moving. With target speed at zero and turning the TDC back on, the path of your torpedo is now determined purely by where you point the periscope.

So for your example -- target going 6 kts passing right to left using medium-speed torpedo ...

MEDIUM torpedo lead angle = approximately 1.5 x Target Speed = 1.5 x 6 kts = 9 degrees of lead angle.

You've set the TDC OFF; set speed to zero; TDC back ON. Looking through your periscope, you see center target bearing 020 relative. Lead the target with your periscope by 9 degrees -- point your periscope at bearing 011 degrees relative -- and shoot.

Don't forget to open the bow cap (torpedo door) before you shoot. For a target at close range, it can move several degrees in the time it takes to get the bow cap open.

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To answer your second question -- yes, you are altering the gyro angle with your periscope, which is exactly what you want to do -- you want to alter the gyro angle to lead the target by some number of degrees that you've computed in your head. The only difference between a true TDC solution and the "snap shot" is you are computing the lead based on torpedo speed, your best estimate of target speed, and a rule-of-thumb calculation and using the periscope to apply that lead against the target.

01-31-12, 01:01 PM	#7
Alfred Keitzer Kapitän zur See Join Date: Jun 2007 Location: San Diego, CA Posts: 93 Downloads: 264 Uploads: 0	Not quite -- you can do it that way, but not required. You don't have to leave the periscope at 0 -- that was just for the demo so you could see the lead (off the nose) computed for different target speeds; and to show you how range has little to no effect on lead angle provided you are shooting within 30-35 degrees of your bow (or stern). Momentarily turning the TDC off, you have control over the TDC settings. Setting the target speed to zero causes the TDC to compute zero lead angle -- because it thinks the target is not moving. With target speed at zero and turning the TDC back on, the path of your torpedo is now determined purely by where you point the periscope. So for your example -- target going 6 kts passing right to left using medium-speed torpedo ... MEDIUM torpedo lead angle = approximately 1.5 x Target Speed = 1.5 x 6 kts = 9 degrees of lead angle. You've set the TDC OFF; set speed to zero; TDC back ON. Looking through your periscope, you see center target bearing 020 relative. Lead the target with your periscope by 9 degrees -- point your periscope at bearing 011 degrees relative -- and shoot. Don't forget to open the bow cap (torpedo door) before you shoot. For a target at close range, it can move several degrees in the time it takes to get the bow cap open. ------------------- To answer your second question -- yes, you are altering the gyro angle with your periscope, which is exactly what you want to do -- you want to alter the gyro angle to lead the target by some number of degrees that you've computed in your head. The only difference between a true TDC solution and the "snap shot" is you are computing the lead based on torpedo speed, your best estimate of target speed, and a rule-of-thumb calculation and using the periscope to apply that lead against the target. Last edited by Alfred Keitzer; 02-01-12 at 02:53 AM.