E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Before the Mast.
To serve before the mast. To be one of the common sailors, whose quarters are in the forward part of the ship. The half-deck is the sanctum of the second mate, and, in Greenland fishers, of the spikeoneer, harpooners,
carpenters, coopers, boatswains, and all secondary officers; of low birth.
I myself come from before the mast.Sir W. Scott: The Antiquary, chap. xx.