Nah, there are two different stats to worry about with hull damage:
1. Armour piercing
Your ship has a fixed hull hardness based on what ship it is and weapons pierce this based on their armour-piercing rating.
Example - An AspX has a hardness of 52. C2 multicannons have a piercing value of 37, C3 multicannons have a piercing of 54.
So the 52 hardness is more than the C2 multicannon piercing, meaning that some of the damage fails to pierce the armour. 37/52 = 71% of the damage gets through, 29% is ignored completely.
Meanwhile, C3 multicannons with a piercing value of 54 fully pierce the hull hardness and always do 100% of their damage against an AspX before resistances.
After the incoming damage has has been modified for piercing vs hardness, and then modified again vs resistances, you have the RAW damage that gets done;
Let's take a stock AspX and the C2 multicannon again; 71% of the damage makes it past hull hardness, so that's a 0.71 multiplier. Kinetic rounds do 1/(100%-20%)=1.25 because of the -20% kinetic resists.
Each individual multicannon round does 2.2 damage, so 2.2 x 0.71 x 1.25 = 1.95 RAW damage.
RAW damage is done to something's integrity, either the hull or a module and to decide what that is you need to understand penetration chance.
2. Penetration chance
So, that single multicannon round did 1.95 RAW damage.
If it hits the spherical hit-zone of an external module first, then 1.95 integrity is deducted from that module.
If it misses an external module, then there is first of all a penetration check; Many weapons have a 40-80% penetration chance.
At 100% hull integrity (immediately after shields have dropped for the first time) there is a 40% chance that 1.95 RAW damage will penetrate.
At almost 0% hull integrity (immediately before the AspX explodes) there is an 80% chance that 1.95 RAW damage will penetrate.
If the round fails to penetrate, that's 1.95 RAW damage to hull integrity. Nice and easy so far.
If the round penetrates, a check is made to see if it hits any internal modules. Pretty much everything except super penetrator rounds go just over half-way through the hull before stopping.
If no modules are hit, all 1.95 RAW damage is deducted from hull integrity.
If the round penetrates and hits a module, most of the 1.95 RAW damage is done to the module, and a small fraction is done to the hull integrity.
I don't actually know what the ratio is but it's probably 2:1 because FDev like that ratio for the word "most". That means 1.3 RAW damage to the module and 0.65 RAW damage to the module.
In summary then an incoming round goes through the following two modifiers:
1) Armour vs hull hardness
2) damage type vs hull resistance
Then penetration determines whether the remaining RAW damage gets done to hull or modules.
There's an interesting quirk of penetration, which explains the phenomenon of ships being seemingly soft as butter immediately after the shields drop, but then their hull drops more slowly the closer they get to death.
The reason for this is that with high hull percentage, there's a 60% chance the shot *won't* penetrate, so lots of your shots will reduce your target's hull integrity. As their hull integrity drops closer to zero, 80% of your shots are penetrating and there's a very high chance this damage is being soaked up by modules instead, which makes it seem like the hull is actually getting tougher. I guess in reality there's just less of it less to actually hit and the bulkheads are more hole than they are bulkhead at this point!
