Sentence:  [...] but under certain circumstances (night watches on a whaling ground) the command of the ship's deck is also his; therefore the grand political maxim of the sea demands, that he should nominally live apart from the men <WSD>before the mast</WSD>, and be in some way distinguished as their professional superior; [...] 
Meaning of the word marked with <WSD> tags:  Describing seamen rather than officers