Damage model
 

Salute!

Can you damage a rudder or screws of the ship with torpedo or gun impact?

I remember impacts in the stern with no results.

If not, do you know any mod to fix it?

Thanks

If the damage model is done correctly?
Yes, you can destroy them.

I've never seen a rudder destroyed, but I have seen ships loose their screws after a hit to the stern..

I've only hit a merchant in the stern once, right where the rudder and screws are. The merchant lost all it's speed so my guess is that stern damage is modeled in the game.

I agree with the prop damage, but I've never seen a ship with the rudder blocked, turning endless like Bismarck in RL.

It won't block a rudder but they can be destroyed if the damage model has it zoned properly.
They break off and/or disappear.

So she won't turn anymore? Or is just cosmetic?

Only cosmetic in my opinion.
Just like when the ship looses it's screws graphically, it may still be propelled for a couple of minutes (propeller sound still there, and ship moving)