Hull protection

Sacrificial Anodic Protection

1. Sacrificial anodes work on the principle of electrolysis,
2. an anode and a metallic strip are dipped in electrolytic solution, 
3. Anode electron will dissolve and deposit over the metallic strip and make it a cathode.
4. Seawater acts as an electrolyte and transfers the electrons from the anode to the steel plate and making a protecting layer.
5. If the metal is more active it will be easily oxidized and will protect the metallic compound by making it act as cathode
6. The anode will corrode first sacrificing itself for the other compound and it is thus called sacrificial anode
7. Active means more electrochemical potential. ( magnesium, aluminium and zinc) 

Impressed Current Catholic Protection

Parts to be protected are made cathodic, 

The anode does not corrode as electric is not generated by it but impressed on it 

The electric current is supplied from ship supply and converted to low dc voltage

Current is impressed on anodes to reduce the potential difference between hull and anode. Hence no chemical reaction

Reference cell control the amount of current, 

If too low, corrosion takes place 

If too much will damage paint and protective coatings

Hull painting

1. International Convention of Anti fouling system to ban the use of harmful substance in anti-fouling paints used on ship hull.
2. Anti-fouling paints  are used to coat bottom of ship to prevent sea life from attaching themselves to hull, which slowing the ship increasing the fuel consumption
3. Anti-fouling system is coating, paint, surface treatment, device used on ship to prevent fouling
4. In the past, metallic compound are used which affect marine life. In the past anti-fouling paint contain TBT, causes harm to marine life,
5. Todays technology anti-fouling paint, do not contain TBT, provide slippery surface preventing fouling and making easier to clean.
6. Also self eroding pain which uses weaker biocide, self eroding paint get eroded slowly, and biocide acts as toxin for marine growth.

quotes: https://www.marineinsight.com/tech/understanding-sacrificial-anodes-on-ships/