Mad as the sea and wind when both contend
Which is the mightier

Gertrude uses this vivid simile to describe Hamlet’s madness to Claudius in the brief first scene of Act 4, in which Claudius decides to ship off Hamlet to England. Her hyperbolic language here leaves no doubt over where she stands on the question of whether her son is feigning madness or is truly mad. Keep in mind that she says this shortly after having witnessed Hamlet kill Polonius and viciously berate her for her role in the murder of King Hamlet, so her vehemence is entirely understandable.