It's awesome how many people still don't know this.
These are some tests made on our fleet long time ago.
SS1 ijn torps against a QV.
Values are very accurate since they are the mean of 5 taken values.
Torps were aimed very carefully to the exact center of the ship.
Test were made with 0, 0.1, 0.2,0.3, 0.4, 0.5, 1.0, 2.0, 3.0. 6.0, 12.0 and 24.0 on belt. The point where the half reduction starts is 0.2 belt. It show the % of damage taken from the torp versus the amount of belt put.
As you see, putting more than 0.2 belt will not have noticable effect. So, to all that people that put 1.0 belt, 3.0 belt or don't put belt at all just take a look on that graphic for see how belt works against torps.
So, the armor configuration for the 99% of ships in the game is 0.2 belt and the rest you can put without loosing speed, put it on bulge.
If you didn't know 0.2 belt reduce the damage of torps by half then see this other pic, from a test from emu long time ago too.
That means torps will make you maximum damage on the center of the ship, and more or less half of that damage in a extrem of the ship.
So, knowing both things you can reduce the damage taken from torps by 4.
Sure many people know this, but others, don't.