aback of

— […] to effect which they must beat to windward for several days, between the west end of Cuba and the south coast of East Florida, till they get as far to the eastward as the Pan of Matanzas, a mountain so called, just aback of the town of the same name, say thirty leagues to the east of the Havanna, opposite which the gulph stream turns to a due north direction, which had been before east, and runs three, four, and five knots an hour […]