Evaluate a couple of vessels rounding end of cape (6)
I believe the answer is:
assess
'evaluate' is the definition.
(synonyms)
'a couple of vessels rounding end of cape' is the wordplay.
'couple of vessels' becomes 'SS SS' (SS can mean a steamship).
'rounding' is an insertion indicator (some letters go round others).
'end of' suggests the final letters.
The last letter of 'cape' is 'e'.
'ssss' placed around 'e' is 'ssess'.
'a'+'ssess'='ASSESS'
(Other definitions for assess that I've seen before include "Estimate the worth or quality of" , "Evaluate, estimate" , "Appraise, estimate value" , "price" , "Make estimate or appraisal of" .)