Sentence:  It is never possible to settle down to the ordinary routine of life at sea until the screw begins to revolve. There is an hour or two, after the <WSD>passengers</WSD> have embarked, which is disquieting and fussy. 
Meaning of the word marked with <WSD> tags:  One who rides or travels in a vehicle, but who does not operate it and is not a member of the crew.