Animal Slaughtering

Is it permissible to say the intention aloud when I want to slaughter a sacrifice on behalf of my deceased father and I say, “O Allah, it is the udhiyah (sacrifice) for my father so-and-so.” Or is it sufficient simply to do the deed without saying anything aloud?

Is it permissible to offer a sacrificial animal that has some defects in its body? What if I bought an animal that was good and free from defects and then the animal got some defect like having its leg broken or something like that. Is it still valid to use it?