Gritty characters in boats and yachts (5)
I believe the answer is:
sandy
'gritty' is the definition.
(synonyms)
'characters in boats and yachts' is the wordplay.
'characters in' indicates a hidden word.
'SANDY' is hidden within 'boats and yachts'.
(Other definitions for sandy that I've seen before include "Like a beach perhaps" , "Hair colour" , "gritty" , "Alexander (abbrev.)" , "(Of hair)light yellowish brown" .)