Capital sailor finally breaks white whale at sea (11)
I believe the answer is:
wherewithal
'capital' is the definition.
(wherewithal is a kind of capital)
'sailor finally breaks white whale at sea' is the wordplay.
'finally' suggests the final letters.
'breaks' is an insertion indicator.
'at sea' is an anagram indicator.
The last letter of 'sailor' is 'r'.
'white'+'whale'='whitewhale'
'whitewhale' with letters rearranged gives 'wheewithal'.
'r' inserted inside 'wheewithal' is 'WHEREWITHAL'.
(Other definitions for wherewithal that I've seen before include "Means" , "(The) necessary" , "Resources" , "Essentials" , "Money needed for some purpose" .)