A scraggy old woman, a vixen; so called by a play on the first syllable. It properly means a raft consisting of three sticks, lashed together with ropes; used on the coasts of Coromandel and Madras.
“No, you old catamaran, though you pretend you never read novels. ...” —Thackeray: Lovel the Widower, chap. i.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on Catamaran from Infoplease: