Zinc and aluminium
Cathodic protection is best known as a technique that helps control and prevent a metal surface from corroding. The technique accomplishes this by turning that metal surface into an electrochemical cell’s cathode. This essentially links the protected metal to another type of metal (as a stand in) that acts as an anode.
The ‘sacrificial’ anode in this case is a type of metal anode that is more reactive to the structure’s (in this case, ship’s) natural corrosive environment. When it’s in place (electrically linked), it protects the structure’s metal by incurring the corrosive damaged instead. Ships and other water craft made from easily corroding metals use anodes as a way to prevent the hull and other metal structures on the ship from corroding over time.