Vessels moving up Southern Point (4)
I believe the answer is:
cusp
'point' is the definition.
(I know that cusp is a type of point)
'vessels moving up southern' is the wordplay.
'vessels' becomes 'c' (I can't explain this - if you can you should give a lot more credence to this answer).
'moving' is an anagram indicator (letters are moved around).
'southern' becomes 's' (abbreviation).
'up'+'s'='ups'
'ups' anagrammed gives 'usp'.
'c'+'usp'='CUSP'
Can you help me to learn more?
(Other definitions for cusp that I've seen before include "Pointed meeting of curves" , "Point where two curves meet - point of transition" , "Horn of moon" , "Pointed end where two curves meet" , "Point of transition, brink" .)