The idea of death is introduced earlier on in the phrase 'peripatetic sarcophagus' - not that people in hansom cab's usually died (). It's just that if the cab were a 'sarcophagus' the cabby would know where it was bound.
The idea of a nautical image is introduced by the word 'aloft', which was used - in pre-radio, pre-GPS days - to refer to the highest point on a ship's main-mast, where there was a platform called a 'crow's nest'. A man who was 'aloft' was in the crow's nest looking for land or another sail. (This is not to say that 'aloft' wasn't also used to mean something like 'up there' in non-sea-faring contexts. But aloft, with no precise statement of whereabouts ('he's aloft in the tree'), has a specific meaning on ships even when there's no statement of whereabouts; if a man's 'aloft', he's in the crows nest or up in the rigging - an old sea song has the chorus
While raging sea did roar
And the story winds did blow
And we jolly sailor-boys were up up aloft
And the land-lubbers lying down below...
Another song, Tom Bowling uses the ambiguity of 'aloft' in reference to a dead (but peacefully retired) sailor: 'Tom has gone aloft'.
It's really quite a 'pregnant' passage.