Green’s Dictionary of Slang

tide n.

SE in slang uses

In phrases

get under the tide (v.) (also get under)

(US/Aus.) to become very drunk.

1899–1900		C.L. Cullen Tales of the Ex-Tanks 259: He never got under the tide, either, but was [...] sensible enough to keep just on edge and no more.
1957		J. Hawke Follow my Dust! 173: You’re drunk, pal. Haw, haw! Your own brew ’as got you under.