Three Minute Rule

[subcpo]

12 Knots in 3 minutes....1200 Yards

To figure out how far you will go in 3 minutes..take speed and add two 00's

[mrbeast]

Cheers subcpo

Love little bits of knowledge and short cuts that RL skippers used.

I've got one I learned a rough way to calculate how many degrees to lead a target.

Used by S boat skippers who didn't have the luxury of a TDC:

Speed + 3 = how many degrees to lead the target

[Rockin Robbins]

Originally Posted by mrbeast

Cheers subcpo

Love little bits of knowledge and short cuts that RL skippers used.

I've got one I learned a rough way to calculate how many degrees to lead a target.

Used by S boat skippers who didn't have the luxury of a TDC:

Speed + 3 = how many degrees to lead the target

OOOOO that's a technical one. Actually that doesn't work, but I can tell you what does work and you can still figure it in your head. First of all the lead angle depends also on the speed of the torpedo, so one rule does not fit all. Let's just fit the steam torpedoes.

First, let's disprove the speed+3 rule. With fast setting, the proper lead for a target moving at right angles to the torpedoe's path at a speed of 13 knots is.....16º. Hmmmmm. That's speed+3, isn't it. But for a ship traveling 1 knot the angle is 1º. for 6 kt, the angle is 7.5º.

With slow setting things fall apart quickly. For 5 kt the lead angle is 9º. For 20 kt the lead angle is 33º, a bit more than speed+3º. So you can see that speed+3 isn't going to hit much except on fast torpedoes with target speeds between 13 kt and 20 kt, and slow torpedoes on targets between 4 kt and 4 kt (only works for that speed!).

So what works? I discovered that for fast torpedoes, the lead angle is target speed x 1.2º. 10 knots x 1.2º gives you a lead angle of 12º. For slow torpedoes, the multiplier is 1.8. A 10 knot target would have to be led by 18º for slow torpedoes. These rules work for all target speeds at right angles to the torpedo track. So to summarize.

Fast torpedoes: target speed x 1.2 degrees
Slow torpedoes: target speed x 1.8 degrees

Now the deal killer. All the above is totally unimportant because you don't need to know any of it! If your target speed is 10 kt, just feed that into your TDC and hit the send button. DO NOT turn on the PK. Now all you have to do is point the periscope where you want the ship to be when you shoot (this angle should be at right angles to target path and within +-15º of your own heading) and hit the range/bearing send button. Remember the bearing. You can unlock the periscope and look around all you want without messing up the setup. When the target gets close to the bearing, just reaim the scope on that bearing. When the juicy parts of the ship go by the crosshair, shoot the fish of your choice, fast or slow. The TDC will calculate the angle and hit the ship exactly where the crosshair was when you pulled the trigger. No rule necessary! Complete instructions with pictures can be found at http://www.subsim.com/radioroom/show...6&postcount=67.

Now the rule is just to impress the babes in the bar after the cruise!