Play the part of the harbourman (7)
I believe the answer is:
portray
'play' is the definition.
(portraying is a kind of playing)
'the part of the harbourman' is the wordplay.
I cannot really understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is located in the answer.
'part' could be 'ray' (ray is a kind of part) and 'ray' is found within the answer.
'of' could be 'o' and 'o' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for portray that I've seen before include "Delineate" , "Use words to describe" , "Act" , "Describe in words or make a picture" , "Depict in art" .)