Green’s Dictionary of Slang

boat and oar n.

a prostitute.

1935		A.J. Pollock Und. Speaks 10/2: Boat and oar, a whore. [Ibid.] 14/1: Broken oar, a whore.
1939		D. Maurer ‘Prostitutes and Criminal Argots’ in Lang. Und. (1981) 117/1: bladder. An unattractive prostitute. Also beetle, blister, boat-and-oar [...], each expressing varying degrees of unattractiveness.
1960		J. Franklyn Dict. of Rhy. Sl.
1960		(con. 1950-1960) R.A. Freeman Dict. Inmate Sl. (Walla Walla, WA) 14: Boat-’n-oar – whore.
1984		McConville & Shearlaw Slanguage of Sex.
2003		B. Dark Dirty Cockney Rhy. Sl. 25: Don’t listen to her – she’s a lying boat and oar!