The way out, as on ship (6)
I believe the answer is:
egress
'the way out' is the definition.
(I've seen this before)
'as on ship' is the wordplay.
'as' becomes 'eg' (I've seen this in other clues).
'on' becomes 're' ('on' can be mean 'with reference to').
'ship' becomes 'ss'.
'eg'+'re'+'ss'='EGRESS'
(Other definitions for egress that I've seen before include "Escape route" , "Taking leave" , "Way out of serges" , "Issue" , "Way out, departure" .)