The application of antifouling paints to the surfaces of marine installations is the most economically efficient means for mitigating damage caused by marine biofouling in the shipping industry. However, conventional antifouling paints currently in widespread use can no longer meet the requirements of green antifouling. Although hydrogel coatings have made great progress in marine antifouling applications, current hydrogel coatings still suffer from construction difficulties and poor mechanical stability under wet conditions. In this paper, we innovatively exploit the phenomenon of the absorption of pyrogallol (PG) by large-molecular-weight polyvinylpyrrolidone (PVP), resulting in hydrophilic copolymer macromolecules, to propose a prepolymer-reactor rapid contact molding of sprayable hydrogel coatings. The PG/PVP copolymer produced microscopic reticular mimetic mussel adhesion protein (MAP) bioscaffolds via the chemical crosslinking of polyethyleneimine (PEI), contributed to the conversion of PG to PG-quinone upon the introduction of vanadium pentoxide particles, increased the hydrophobicity of the system and enhanced waterproof adhesion. The wet adhesion of the hydrogel coatings was measured up to 3.42 MPa via the micrometer scratch method, indicating that the prepared hydrogel coating had a stable adhesive force in a wet environment. The hydrogel coating was instantly molded on the surface of 304 stainless steel (SS) via two-step spraying. The swelling, friction, antifouling, and anticorrosion properties of the coatings were investigated along with the wet adhesion strength on the SS surfaces. The results showed that the hydrogel, after double cross-linking of PEI and V₂O₅, had a swelling rate within 30% and a low modulus along with stable lubricating properties. After the formation of the hydrogel coating, the inhibition rate of common bacteria and algae in the ocean reached more than 99%, and the electrochemical corrosion protection rate of SS reached 63.49%. This study provided ideas for improving the wet adhesion of hydrophilic marine antifouling coatings.