Wave's concave shape beneath hulls (8)
I believe the answer is:
brandish
'wave's' is the definition.
(synonyms)
'concave shape beneath hulls' is the wordplay.
I cannot really understand how this works, but
'shape' could be 'dish' (dishing is a kind of shaping) and 'dish' is found within the answer.
The remaining letters 'bran' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for brandish that I've seen before include "Wield or wave belligerently" , "Wave as a threat" , "Wave, flourish" , "Wave something about threateningly" , "Triumphantly draw attention to" .)