A steel ship would have a life expectancy of 20~25 years before being scraped, which is strongly affected by the life-time of the ballast tanks. The ballast tanks are directly exposed to seawater and continuously subjected to fluctuations of sea water due to the pitching and rolling of the ship as well as to external loads such as hogging and sagging of the hull. As a result, the interior tank paint of the ballast tank is vulnerable to exfoliation due to its poor durability even small external shocks. Furthermore, under wet-dry cycling condition or empty condition of the tank, the application of corrosion protection using sacrificial anode is limited. It leads to more serious corrosion damages and sudden shortening of the ship''s life. Therefore, in this study, the metal thermal spray coating technique was used to prevent the ballast tank from corrosion damage. Al, Zn and Al-Zn alloys as thermal spray coating feedstock material for corrosion protection of the steel against marine environment are mainly used, but in this investigation, Al, Al-3%Mg, Al-5%Mg, Zn, and Inconel 625 were used. Furthermore, for comparative studies of the corrosion resistance and durability of various thermal spray coating layers, static and dynamic hybrid experiments were conducted. As a result, the Inconel 625 thermal spray coating was determined to be the most excellent thermal spray coating material for the seawater environment. While having presented the best corrosion resistance and anti-cavitation characteristics, the Inconel 625 may easily establish a small anode-large cathode situation for the substrate material(SS400). Consequently, the Al-3%Mg thermal spray coating layer was determined to be the best thermal spray coating material in this paper, which has the second highest in cavitation resistance next to the Inconel 625 thermal spray coating layer, while having a sufficient driving force and the lowest corrosion rate for sacrificial anodic protection of SS400 steel. Furthermore, a post-treatment of the organic-inorganic composite ceramic(hybrid sealing) was performed to improve such defects as the intrinsic pores in the coating layer during the Al-3%Mg thermal spray coating process. As a result, even though corrosion resistance in static conditions improved by about 92 %, when physical external forces such as micro-jet and shock-wave of cavitation were applied, the corrosion resistance and durability were similar to its characteristics due to the poor durability of the hybrid sealing itself. Therefore, in the case of the Al-3%Mg thermal spray coating layer, the application of hybrid sealing should be carefully considered after evaluation of the external environment so as to enhance corrosion resistance or avoid economic losses due to unnecessary work.