Boatman heading north, in relation to the shorter Caribbean island (7)
I believe the answer is:
yachter
'boatman' is the definition.
(thesaurus)
'heading north in relation to the shorter caribbean island' is the wordplay.
'heading north' is a reversal indicator.
'in relation to' becomes 're' (regarding**).
'shorter' means to remove the last letter.
'caribbean island' becomes 'cay' (type of topical island as found in the Caribbean).
'the' with its last letter removed is 'th'.
're'+'th'+'cay'='rethcay'
'rethcay' written backwards gives 'YACHTER'.
(Other definitions for yachter that I've seen before include "person on board?" , "sailor" .)