Having living quarters in the forecastle(adjective)
Describing seamen rather than officers(adjective)
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Use "before the mast" in a sentence
"The month in which my seventeenth birthday arrived I signed on before the mast on the Sophie Sutherland, a three-topmast schooner bound on a seven-months 'seal-hunting cruise to the coast of"
"Subsequently I shipped before the mast and sailed for the Japanese coast on a seal-hunting expedition, later going to Behring Sea."
"Richard H. Dana served two years before the mast, and had every experience that falls to the lot of the sailor before the mast of our day."