Take on a steamship, I say, you and me (6)
I believe the answer is:
assume
'take' is the definition.
(I know that assume is a more specific form of the action take)
'on a steamship i say you and me' is the wordplay.
'on' says to put letters next to each other.
'a steamship' becomes 'ss' (nautical abbreviation).
'i' becomes 'a'.
'say' indicates a 'sounds like' (homophone) clue.
'and' is a charade indicator (letters next to each other).
'you' sounds like 'u'.
'ss' put after 'a' is 'ass'.
'ass'+'u'+'me'='ASSUME'
(Other definitions for assume that I've seen before include "Take to be the case" , "Take (responsibility)" , "Suppose - appropriate - feign - adopt" , "Be arrogant" , "Take as true or take for granted" .)