Too much rudder admits first watch to master (9)
I believe the answer is:
overwhelm
'master' is the definition.
(thesaurus)
'too much rudder admits first watch' is the wordplay.
'too much' becomes 'over' (I've seen this before).
'rudder' becomes 'helm' (I've seen this before).
'admits' is an insertion indicator.
'first' says to take the initial letters.
The initial letter of 'watch' is 'w'.
'over'+'helm'='overhelm'
'overhelm' enclosing 'w' is 'OVERWHELM'.
'to' acts as a link.
(Other definitions for overwhelm that I've seen before include "Completely defeat" , "Bury or drown beneath a huge mass of something" , "Snow under" , "Conquer" , "Overcome by superior force" .)